Cortese Et Al 2008-Critical Reviews in Food Science

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Attention-Deficit/Hyperactivity Disorder (ADHD) andObesity: A Systematic Review of the LiteratureSamuele Cortese M.D. a b , Marco Angriman M.D. b , Claudio Maffeis M.D. c , Pascale IsnardM.D. a , Eric Konofal M.D., Ph.D. a , Michel Lecendreux M.D. a , Diane Purper-Ouakil M.D.,Ph.D. a d , Brenda Vincenzi M.D. b , Bernardo Dalla Bernardina M.D. b & Marie-ChristineMouren M.D. aa AP-HP, Child and Adolescent Psychopathology Unit, Robert Debré Hospital, Paris VIIUniversity, Paris, Franceb Child Neuropsychiatry Unit, G.B. Rossi Hospital, Department of Mother-Child and Biology-Genetics, Verona University, Verona, Italyc Pediatric Unit, G.B. Rossi Hospital, Department of Mother-Child and Biology-Genetics,Verona University, Verona, Italyd INSERM U 675 Analyse Phénotypique, Développementale et Génétique des ComportementsAddictifs, Faculté Xavier Bichat, 75018, Paris, France

Available online: 05 Jun 2008

To cite this article: Samuele Cortese M.D., Marco Angriman M.D., Claudio Maffeis M.D., Pascale Isnard M.D., Eric KonofalM.D., Ph.D., Michel Lecendreux M.D., Diane Purper-Ouakil M.D., Ph.D., Brenda Vincenzi M.D., Bernardo Dalla Bernardina M.D.& Marie-Christine Mouren M.D. (2008): Attention-Deficit/Hyperactivity Disorder (ADHD) and Obesity: A Systematic Review ofthe Literature, Critical Reviews in Food Science and Nutrition, 48:6, 524-537

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Critical Reviews in Food Science and Nutrition, 48:524–537 (2008)Copyright C©© Taylor and Francis Group, LLCISSN: 1040-8398DOI: 10.1080/10408390701540124

Attention-Deficit/HyperactivityDisorder (ADHD) and Obesity: ASystematic Review of the Literature

SAMUELE CORTESE, M.D.,1,2 MARCO ANGRIMAN, M.D.,2 CLAUDIOMAFFEIS, M.D.,3 PASCALE ISNARD, M.D.,1 ERIC KONOFAL, M.D., PH.D.,1

MICHEL LECENDREUX, M.D.,1 DIANE PURPER-OUAKIL, M.D., PH.D.,1,4

BRENDA VINCENZI, M.D.,2 BERNARDO DALLA BERNARDINA, M.D.,2 andMARIE-CHRISTINE MOUREN, M.D.11AP-HP, Child and Adolescent Psychopathology Unit, Robert Debre Hospital, Paris VII University, Paris, France2Child Neuropsychiatry Unit, G.B. Rossi Hospital, Department of Mother-Child and Biology-Genetics, Verona University,Verona, Italy3Pediatric Unit, G.B. Rossi Hospital, Department of Mother-Child and Biology-Genetics, Verona University, Verona, Italy4INSERM U 675 Analyse Phenotypique, Developpementale et Genetique des Comportements Addictifs,Faculte Xavier Bichat, 75018 Paris, France

Recent studies suggest a possible comorbidity between Attention-Deficit/Hyperactivity Disorder (ADHD) and obesity. Togain insight into this potential association, we performed a systematic review of the literature excluding case reports, non-empirical studies, and studies not using ADHD diagnostic criteria. Empirically based evidence suggests that obese patientsreferred to obesity clinics may present with higher than expected prevalence of ADHD. Moreover, all reviewed studies indicatethat subjects with ADHD are heavier than expected. However, data on the prevalence of obesity in subjects with ADHD arestill limited. As for the mechanisms underlying the potential association between ADHD and obesity, ADHD might lead toobesity via abnormal eating behaviors, impulsivity associated with binge eating might contribute to ADHD in obese patients,or, alternatively, both obesity and ADHD might be the expression of common underlying neurobiological dysfunctions, atleast in a subset of subjects. In patients with obesity and ADHD, both conditions might benefit from common therapeuticstrategies. Further empirically based studies are needed to understand the potential comorbidity between obesity and ADHD,as well as the possible mechanisms underlying this association. This might allow a more appropriate clinical managementand, ultimately, a better quality of life for patients with both obesity and ADHD.

Keywords obesity, overweight, ADHD, inattention, hyperactivity, impulsivity, pharmacological treatment

INTRODUCTION

Attention-Deficit/Hyperactivity Disorder (ADHD) is one ofthe most common childhood psychiatric disorders, estimated toaffect 5–10% of school-aged children worldwide (Biederman,2005). According to the Diagnostic and Statistical Manual ofMental Disorders-4th edition (DSM-IV) (APA, 1994) and itsupdated version (Text Revision, TR) (APA, 2000), ADHD isdefined by a persistent and age-inappropriate pattern of inatten-tion, hyperactivity-impulsivity, or both. Onset before the age ofseven and impaired functioning in two or more settings are re-

Address correspondence to: Samuele Cortese, M.D., Service de Psy-chopathologie, de l’Enfant et de l’Adolescent, Hopital Robert Debre, 48 Boule-vard Serurier, 75019 Paris, France. Tel : +33140032263, Fax: +33140032297.E-mail: [email protected]

quired for the diagnosis. The DSM-IV (APA, 1994) and IV-TR(APA, 2000) define four types of ADHD: “predominantly inat-tentive,” “predominantly hyperactive-impulsive,” “combined,”and “not otherwise specified.” Deficits in executive functions,including inhibition, working memory, planning, and sustainedattention, are common, although far from universal, in ADHD(Biederman and Faraone, 2005). Impairing symptoms of ADHDmay persist into adulthood in up to 60% of cases (Kessler et al.,2005). Stimulants (methylphenidate and amphetamines) are thefirst-line FDA-approved pharmacological treatment, followedby the non-stimulant atomoxetine (Pliszka et al., 2006).

It is well known that ADHD is frequently associated withpsychiatric and developmental disorders such as OppositionalDefiant Disorder, Conduct Disorder, Anxiety Disorders, De-pressive Disorders, Speech and Learning Disorders (Dulcan,

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ATTENTION-DEFICIT/HYPERACTIVITY DISORDER (ADHD) AND OBESITY 525

1997).7 Although overlooked in the past, a possible new co-morbidity between ADHD and obesity has been suggested byrecent studies (Agranat-Meged et al., 2005; Altfas, 2002; Curtinet al., 2005; Fleming et al., 2005; Holtkamp et al., 2004; Lam andYang, 2007). A better insight into this potential comorbidity is ofrelevance for two reasons. First, it may contribute to the under-standing of possible pathological mechanisms underlying bothADHD and obesity, at least in a subset of patients. Second, froma clinical standpoint, it might have important implications for themanagement of patients with both obesity and ADHD, suggest-ing common and potentially effective therapeutic strategies forthese two conditions when they coexist. This seems particularlynoteworthy because of the high prevalence and the enormouspersonal, familiar, and social burden associated with both obe-sity (Dietz and Robinson, 2005; Malecka-Tendera and Mazur,2006; Speiser et al., 2005) and ADHD (Biederman, 2005).

In light of these considerations, the aims of this paper were:1) to systematically review empirically based evidence on the re-lationship between ADHD and obesity; 2) to examine the mech-anisms which have been proposed to underlie the potential co-morbidity between obesity and ADHD; 3) to discuss the impli-cations of this possible comorbidity on the clinical managementof patients who present with both ADHD and obesity.

Systematic Review of the Literature

In order to gain insight into the relationship between ADHDand obesity, we searched for studies: 1) assessing the prevalenceof ADHD in obese subjects; 2) evaluating the weight status ofsubjects with ADHD.

To this purpose, a PubMed search was performed us-ing the following keywords in various combinations: ADHD,“attention-deficit/hyperactivity disorder,” inattenti,* hyperac-tiv,* impulsiv,* obes,* overweight, weight. Moreover, the termsobes* and overweight were cross-referenced separately withpsychiatr,* psychopatholog,* and psycholog* to look for anyadditional studies on the relationship between obesity and psy-chopathology, including ADHD.

Since the diagnosis of ADHD is based on standardized cri-teria, studies that analyzed the relationship between obesity andADHD traits (i.e. symptoms of inattention, hyperactivity or im-pulsivity), without using formal diagnostic criteria, were notconsidered.

ADHD was differently defined in the previous editions ofthe DSM. The DSM-III (APA, 1980) included the definition of“Attention Deficit Hyperactivity Disorder,” similar to the “com-bined type” of the DSM-IV (APA, 1994). The DSM-III-R (APA,1987) included “Attention Deficit either With or Without Hyper-activity,” similar, respectively, to the “combined” and “inatten-tive” type of the DSM-IV (APA, 1994). Given these similarities,studies based on DSM-III (APA, 1980) or III-R (APA, 1987) cri-teria were retained in our systematic review. On the other hand,the DSM-I (APA, 1952) and II (APA, 1968) were not based onempirical data and explicit diagnostic criteria. Therefore, we ex-

cluded any papers published before 1980 (when the AmericanPsychiatric Association first published the DSM-III).

Reference lists from each relevant paper were examined todetermine if any relevant studies had been missed during thedatabase searches. Studies of both children and adults were con-sidered.

Case reports and descriptive studies with no statistical anal-yses of data were excluded, as well as unpublished data (e.g.,unpublished doctoral dissertations).

Finally, since drugs used for the treatment of ADHD mayhave anorexigenic effects, studies examining weight status intreated subjects with ADHD or studies which did not control forthe effect of treatment were not considered.

Results

The database searches (1980-January 2007) yielded the fol-lowing results: ADHD and obes*: 40 references; “attention-deficit/hyperactivity disorder” and obes*: 40 references; inat-tenti* and obes*: 4 references; hyperactiv* and obes*: 217 ref-erences; impulsiv* and obes*: 49 references; ADHD and over-weight: 24 references; “attention-deficit/hyperactivity disorder”and overweight: 21 references; inattenti* and overweight: 4references; hyperactiv* and overweight: 125 references; im-pulsiv* and overweight: 38 references; ADHD and weight:505 references; “attention-deficit/hyperactivity disorder” andweight: 326 references; inattenti* and weight: 90 references;hyperactiv* and weight: 1554 references; impulsiv* and weight:291 references; obes* and psychiatr*: 1810 references; obes*and psycholog*: 6497 references; obes* and psychopatholog*:249 references; overweight and psychiatr*: 6 references; over-weight and psycholog*: 5746 references; overweight and psy-chopatholog*: 221 references.

Eight studies (Carey et al., 1988; Hellgren et al., 1993; Hwanget al., 2006; Lumeng et al., 2003; Rojo et al., 2006; Strauss et al.,1985; Tersha Kovec et al., 1994; Zeller et al., 2004; McGee et al.,1985) examining symptoms of inattention and/or hyperactivity-impulsivity in obese subjects were not included in our reviewsince they did not use formal diagnostic criteria for ADHD.Results of the study by Vila et al. (2004) were not consid-ered because the authors did not perform statistical analyseson the prevalence of ADHD in their sample. The study by Sar-wer et al. (2006) was also excluded given the lack of a controlgroup. After excluding any other non-pertinent studies, we re-tained ten studies (Curtin et al., 2005; Holtkamp et al., 2004; Lamand Yang, 2007; Anderson et al., 2006; Biederman et al., 2003;Faraone et al., 2005; Spencer et al., 1996, 2006; Swanson et al.,2006; Hubel et al., 2006) evaluating the weight status of subjectswith ADHD and five studies (Agranat-Meged et al., 2005; Al-tfas, 2002; Fleming et al., 2005; Erermis et al., 2004; Mustilloet al., 2003) assessing the prevalence of ADHD in obese vs.control subjects. Among the studies examining the prevalenceof ADHD in obese subjects, we included the report by Fleminget al. (2005). Although these authors did not perform a formal

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526 S. CORTESE ET AL.

diagnosis of ADHD, they used a questionnaire with high sen-sitivity to detect ADHD. Moreover, they combined data fromdifferent questionnaires to classify the subjects as likely casesof ADHD. Therefore, although recognizing that this is not thestandardized procedure to diagnose ADHD, the methodologyused by Fleming et al. (2005) allowed a valid approximation ofADHD formal diagnosis.

The studies retained in our systematic review will be dis-cussed in the following sections.

Studies Examining the Prevalence of ADHD in ObeseSubjects (Table 1)

The first report on the prevalence of ADHD in obese sub-jects was provided by Altfas (Altfas, 2002). In a retrospectivereview of a clinical sample of 215 obese adults receiving obesitytreatment in a bariatric clinic, the author found that 27.4% of allpatients presented with ADHD according to DSM-IV criteria(AD), well above the prevalence of ADHD in the general adultpopulation (about 4%) (Biederman and Faraone, 2005). More-over, 33.5% had ADHD symptoms not meeting full DSM-IVcriteria (ADSx), while 39.1% did not report ADHD symptoms(NAD). After dividing the patients into four obesity classes ac-cording to the NIH classification (NIH, 1998) (class III: extremeobesity, BMI ≥ 40; class I and II: obesity, BMI: 30 to 39.9; andoverweight, BMI: 25 to 29.9), the proportion of patients havingADHD in obesity class III (42.6%) was significantly higher thanthose in obesity class I-II and overweight class (22.8% and 18.9%, respectively) (p = 0.002). Moreover, analysis of variance ofpatients’ BMI at the start of treatment showed a significant dif-ference among the group means (p = 0.003), with AD havinga higher BMI (39.2) than ADSx (35.5) and NAD (34.6). Fishermultiple comparison test found AD differed from ADSx andNAD (AD-ADSx: p = 0.001, AD-NAD: p = 0.01).

In another study, Erermis et al. (2004) assessed the frequencyof mental disorders in a sample of 30 obese adolescents (aged12–16 years) seeking treatment from a pediatric endocrinologyoutpatient clinic, in a non-clinical obese group of 30 obese ado-lescents matched for age and sex, and in an age and sex-matchedcontrol group of 30 normal weight adolescents. Subjects withmental retardation, chronic physical illness and bipolar disor-der, or other psychotic disorders were excluded. The authorsused a non-structured psychiatric interview based on DSM-IV criteria to diagnose several psychiatric disorders, includingADHD. They found that the prevalence of ADHD was signifi-cantly higher in the clinical obese group (13.3%) in comparisonto the non-clinical obese group (3.3%) and the control group(3.3%). One major limitation of the study is the relatively smallsample size. Moreover, the mean BMI was significantly lower innon-clinical obese subjects vs. clinical obese adolescents, lim-iting the validity of the comparison of psychopathology ratesbetween clinical and non-clinical obese subjects.

The potential comorbidity between ADHD and obesity wasconfirmed by Agranat-Meged et al. (2005) in a sample of

26 children (13 male, age range: 8–17 years) hospitalized inan eating disorder unit for the treatment of their refractory mor-bid obesity (BMI > 95th percentile). A very high portion of theparticipants (57.7%) presented with ADHD according to DSM-IV criteria (confirmed by the semi-structured interview Sched-ule for Affective Disorders and Schizophrenia for School-AgeChildren-Present and Lifetime Version, K-SADS-PL (Kaufmanet al., 1997)). This proportion was significantly higher than that(10%) found in the general population in the same age group(p < 0.0001). The prevalence of ADHD was particularly ele-vated in boys (76.9%) but was also significant in girls (38.5%).Interestingly, 60% of the participants had the combined typeof ADHD, while 40% were diagnosed with the predominantlyinattentive type. The exclusion criteria (IQ < 80, developmen-tal or neurological disorders, obesity related to known medicalcauses) were intended to reduce the sample bias that might haveinterfered with the assessment of ADHD. However, the resultsof this study should be considered with caution given that theyrefer to a small clinical sample of hospitalized morbidly obesechildren. The authors pointed out that the selection bias may nothave been relevant, since the prevalence ratio of the subtypesof ADHD and the sex ratio of ADHD participants resembledmore that of community than clinical populations. Although thelack of a clinical control group is the major limitation of thestudy, Agranat-Meged et al. (2005) reported that a retrospectivechart review of their patients with anorexia nervosa revealed aprevalence of ADHD similar to the rate prevalence in the generalpopulation (4.8%), and, therefore, lower than that found in theirobese patients.

As previously stated, although the study by Fleming et al.(2005) did not use a formal diagnosis of ADHD, it was includedin our review since the authors used a highly sensitive instru-ment to detect ADHD and combined data from different ques-tionnaires to obtain a likely diagnosis of ADHD. In a sample of75 obese women (mean age: 40.4 years; BMI ≥ 35) consecu-tively referred to a medical obesity clinic, these authors evaluatedADHD symptoms using the Wender Utah Rating Scale (WURS)(Ward et al., 1993). This is a 61-item retrospective survey of be-haviors characteristic of childhood ADHD. It has been foundthat a cut-off score of 36 on a subset of 25 core items fromthe WURS (WURS-25) could correctly classify 96% of indi-viduals identified as meeting adult criteria for ADHD (Wender,1995). Moreover, Fleming et al. (2005) used the Conners’ AdultADHD Rating Scale (CAARS) (Conners et al., 1999) (a mea-sure of current symptoms of ADHD made up of 7 subscales),and the Brown ADD Scale for Adults (Brown, 1996), that mea-sures five functions, including attention, but not hyperactivity orimpulsivity. It was found that 38.6% of the participants scoredat or above the cut-off of 36 on the WURS, significantly higherthan the 4% prevalence previously reported in a normal sam-ple (p < 0.001) (Ward et al., 1993). The inattention-memory,the impulsivity-emotionality, the DSM-IV-inattentive, and theADHD-index subscales scores of the CAARS were significantlyhigher than the expected frequency (p < 0.001). On the con-trary, the hyperactive-restless and the DSM-IV-hyper-impulse

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Table 1 Studies examining the prevalence of ADHD in obese subjects. Case reports, non empirical studies and studies not using standardized ADHD diagnosticcriteria were excluded

First Mean age (SD)/ageauthor (year) Subjects range (years) Key results Comments

Altfas (2002) 215 obese adults treatedin a bariatric clinic

43.4 (10.9) 27.4% of all patients presentedwith ADHD. The proportion ofpatients having ADHD inobesity class III (42.6%) wassignificantly higher than thosein obesity class I-II andoverweight class (22.8% and18.9 %, respectively) (p =0.002). Patients with ADHDhad a significantly higher BMI(39.2) than patients withoutADHD (34.6) (p = 0.01)

Strength: the first report on theprevalence of ADHD in obesesubjects

Limitations: lack of control group(rates of ADHD in obesesubjects were compared withthose in the generalpopulation); comorbidconditions (e.g., obstructivesleep apnea, depression, andanxiety disorders) were notcontrolled for

Erermis et al. (2004) 30 obese adolescents(clinical), 30 obeseadolescents (nonclinical), 30 normalweight adolescents

Clinical group: boys :13.8 (1.2) girls : 13.8(1.3)

The prevalence of ADHD wassignificantly higher in theclinical obese group (13.3%) incomparison to the non-clinicalobese group (3.3%) and thecontrol group (3.3%)

Strengths: subjects with mentalretardation, any chronicphysical illness or a diagnosisof bipolar disorder/ psychoticdisorders were excluded

Limitations: small sample size; anon structured interview wasused to diagnose ADHD; BMIwas significantly lower innon-clinical obese subjects vs.clinical obese adolescents

Agranat-Meged et al.(2005)

26 obese children in apediatric eatingdisorder unit

13.04 (2.78) 57.7% of children presented withADHD vs. estimates of 10% inthe general population in thesame age group (p < 0.0001).

Strength: subjects with mentalretardation, medical causes ofobesity ordevelopmental/neurologicaldisorders were excludedLimitations: lack of controlgroup; small sample size

Fleming et al. (2005)∗ 75 obese womenconsecutively referredto a medical obesityclinic

40.4 (10.8) 38.6% of the participants scoredat or above the cut-off of 36 onthe WURS, significantly higherthan the 4% prevalencepreviously reported in a normalsample (p < 0.001); theinattention-memory, theimpulsivity-emotionality, theDSM-IV-inattentive, and theADHD-index subscales scoresof the CAARS weresignificantly higher than theexpected frequency; 61% of thepatients had scores at theBrown ADD Scale for Adults,suggestive of probable ADHD;26.6% of the patients wereclassified as likely cases ofADHD (vs. DSM-IV adultprevalence estimates of 3-5%)

Strength: symptoms of bothchildhood and adult ADHDwere assessed

Limitations: no formal diagnosisof ADHD; psychiatriccomorbid disorders were notcontrolled for; lack of controlgroup

Mustillo et al. (2003) 991 youth in the generalpediatric population

Age range: 9-16 The diagnosis of ADHD was notassociated with any of theobesity trajectories (no obesity,childhood obesity, adolescentobesity, and chronic obesity).

Strengths: psychiatriccomorbidities were controlledfor Limitation: diagnosis ofADHD was not based oninformation obtained bymultiple sources

∗Although a formal diagnosis of ADHD was not performed in this study, the authors used a questionnaire with high sensitivity to detect ADHD and combined datafrom different questionnaires to classify the subjects as likely cases of ADHD. WURS: Wender Utah Rating Scale; CAARS: Adult ADHD Rating Scale.

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subscales scores did not significantly differ from the referencenorms. Sixty-one percent of the patients had scores higher thanthe 93rd percentile at the Brown ADD Scale for Adults, sugges-tive of probable ADHD. Finally, 26.6% of the patients were clas-sified as likely cases of ADHD on the basis of the combination ofa childhood history of ADHD, as indicated by an elevated WURSsubscore (≥36), and two elevated CAARS symptom scales (T≥ 65). This prevalence was well above the DSM-IV adult preva-lence estimates of 3–5% (APA, 1994). Clearly, since these datawere collected using the patients as the exclusive source of in-formation and no formal diagnosis was obtained, the authorscould not rule out the possibility that these symptoms may havebeen the expression of other psychiatric disorders such as de-pression, anxiety, or sleep disorders. Moreover, all the patients inthis study were women, preventing the generalizability of thesefindings to men.

All the above reviewed studies were conducted in clinicalsettings, and, therefore, their results may not reflect the preva-lence of ADHD in obese persons in the general population. It isof interest, therefore, to look at the prevalence of ADHD (diag-nosed according to standardized criteria) in obese persons in thegeneral population as reported in epidemiological surveys. Inthe only non-clinical study assessing the prevalence of ADHDin obese persons that we found, Mustillo et al. (2003) evaluatedannually, over an 8-year period, the weight status and psychi-atric disorders in a sample of 991 youths aged 9–16 years. Onthe basis of their weight status during the study period, partic-ipants were divided into four obesity trajectories: no obesity,childhood obesity, adolescent obesity, and chronic obesity (obe-sity was defined as BMI age- and sex- specific percentiles >95th

according to the growth charts of the Centers for Disease Con-trol and Prevention (Kuczmarski et al., 2000)). The psychiatricassessment was performed using the Child and Adolescent Psy-chiatric Assessment (CAPA) (Angold et al., 1999), which is aninterviewer based interview with both the child and the parentsand combines the advantages of clinical interviews with those ofhighly structured epidemiologic interview methods, providing apsychiatric diagnosis according to the DSM-IV criteria. Whileoppositional disorder was more common in chronically obeseboys and girls than non obese group, the diagnosis of ADHDwas not associated with any of the obesity trajectories. A ma-jor strength of this study is the measurement of a wide rangeof risk factors and correlates, including state-of-the-art assess-ment for psychiatric disorder. Moreover, the authors were ableto control for the effect of psychiatric comorbidities. Given thehigh psychiatric comorbidity associated with ADHD, this seemsof relevance in order to understand if the potential associationbetween ADHD and obesity is “true” or is mediated by comor-bid disorders (such as depressive disorders). However, the studyalso had some limitations. The diagnosis of ADHD in clinicalsettings is based on information obtained by multiple sources,such as teachers or other third persons, besides children and par-ents, and this is obviously difficult in a large survey such as thisstudy. Moreover, as stated by the authors, their statistical modeldid not allow them to determine whether an association between

obesity and psychiatric disorders was more likely to occur at aparticular age or if the association existed over time.

In summary, we located four studies (Agranat-Meged et al.,2005; Altfas, 2002; Fleming et al., 2005; Erermis et al., 2004)conducted in clinical settings and one survey (Mustillo et al.,2003) in the general population. All the four studies provideempirically based evidence suggesting a higher than expectedprevalence of ADHD in clinical obese subjects. On the otherhand, the survey by Mustillo et al. (2003) in the general pedi-atric population found no association between ADHD and obe-sity. However, as correctly pointed out by Altfas (2002), clinicalsettings may favor a higher case-finding rate because the oppor-tunity to observe and assess behavior is greater than the methodsof epidemiological surveys. Therefore, the “gold standard“ ofcareful clinical assessment is expected to find more cases of aparticular psychiatric disorder in comparison to the assessmentused in surveys in the general population. This may explain, atleast in part, the discordance in the results between the clinicalstudies (Agranat-Meged et al., 2005; Altfas, 2002; Fleming etal., 2005; Erermis et al., 2004) and the survey (Mustillo et al.,2003) reviewed here.

Studies Assessing the Weight Status of Subjects with ADHD(Table 2)

Spencer et al. (1996) evaluated height and weight in a sampleof 124 males with ADHD (diagnosed according to the DSM-III-R criteria) and 109 normal controls aged 6–17 years. Ex-clusion criteria were IQ less than 80, adopted and stepchildren,major sensorimotor handicaps (paralysis, deafness, blindness),psychosis, autism, suicidality, and mental retardation. Childrenfrom the lowest socioeconomic class were excluded to avoid theconfounds of extreme social adversity. Eighty-nine per cent ofsubjects had received pharmacological treatment at some timein their lives, including stimulants. Fifty-three subjects had re-ceived stimulants (which may have anorexigenic effects) while66 subjects did not receive any stimulant treatment in the past twoyears. The authors derived an age- and height-corrected weightindex from standard growth tables (an index of 100 indicates thata subject’s weight is the average expected weight for height andage; an index greater than 100 indicates greater than the averageexpected weight). ADHD probands were found to have greaterthan average body mass (age- and height-corrected weight in-dex: 109 ±15), although no significant difference was found be-tween the age- and height-corrected weight index of ADHD andcontrol subjects. Interestingly, age- and height-corrected weightindex of untreated ADHD was 115, indicative of overweight.However, this result should be considered with caution giventhe limited number of untreated subjects (N = 13). This wasa 4-year follow-up study and growth measures were obtainedonly at the follow-up assessment. Therefore, height and weightat baseline (before treatment) were not available. Given thatsome psychotropics may have anorexigenic effects, one can-not exclude that age- and height-corrected weight indices of

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Table 2 Studies on the weight status of subjects with ADHD. Case reports, non empirical studies and studies not using standardized ADHD diagnostic criteriawere excluded

First author Mean age (SD)/age(year) Subjects range (years) Key results Comments

Spencer et al.(1996)

124 males with ADHD and109 normal controls

Age range: 6-17 ADHD subjects had greater thanaverage body mass (age- andheight-corrected weight index: 109±15), although no significantdifference was found between theage- and height-corrected weightindex of ADHD and controlsubjects. Age- andheight-corrected weight index ofuntreated ADHD was 115,indicative of overweight

Strength: children from the lowestsocioeconomic class andchildren with majorsensorimotor handicaps(paralysis, deafness, blindness),psychosis, autism, or suicidalitywere excluded

Limitation: the impact ofpsychiatric co-morbid disordersand pharmacotherapy was notassessed

Biederman et al.(2003)

140 ADHD girls and 122female controls

Age range: 6–17 The age-and height-corrected weightindex was greater than average(1.1), although not indicative ofoverweight or obesity. Nosignificant differences were foundbetween ADHD girls and controls,as well as between treated anduntreated subjects. ADHD girlswith comorbid major depression(MD) had a significantly greateraverage height- and age-correctedweight index relative to ADHDgirls without MD (p = .011)

Strengths: the authors controlledfor the effect of co-morbidmajor depression andpharmacotherapy; childrenfrom the lowest socioeconomicclass and children with majorsensorimotor handicaps(paralysis, deafness, blindness),psychosis, autism, or suicidalitywere excluded

Limitation: no information onduration, dose, or interruptionsof stimulant treatment

Holtkamp et al.(2004)

97 inpatient and outpatientboys with ADHD in aChild and AdolescentPsychiatric Department

10 (2) The mean BMI-SDS of ADHDpatients were significantly higherthan the age-adapted referencevalues (p = 0.038). The proportionof obese (7.2%) and overweight(19.6%) participants wassignificantly higher than estimatedprevalence (p = 0.0008 and p =0.0075, respectively).

Strength: children with additionalpsychiatric (e.g. pervasivedevelopmental disorder,psychosis, tics anxiety or mooddisorder), somatic, orneurological disorders wereexcluded by medical history,physical examination, and EEG

Limitations: lack of controlgroup; socioeconomic statusand BMI of parents were notcontrolled for

Curtin et al.(2005)

98 children with ADHD ina tertiary care clinic fordevelopmental,behavioral and cognitivedisorders

Age range: 3–18 29% of children with ADHD were atrisk for overweight and 17.3%were overweight. No significantdifference in comparison to anage-matched reference population.However, the prevalence of at riskfor overweight and overweight inchildren not treated with ADHDdrugs (36% and 23%, respectively)was significantly higher than thatfound in treated participants (16%and 6.3%, respectively) (p < 0.05)

Strength: children underwent athorough physical,neurological, anddevelopmental examination

Limitation: the effect ofpsychiatric comorbidities andmedication other thanmethylphenidate was notcontrolled for

Faraone et al.(2005)

568 children with ADHDenrolled in a study of thesafety of mixedamphetamine salts

Age range: 6–12 At baseline, subjects were heavierthan average (mean BMI z-score= 0.41)

Strength: BMI z-scores werecalculated

Limitations: the effect ofcomorbid psychiatric disorderswas not controlled for; no dataon the prevalence of obesity oroverweight(Countinued on next page)

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Table 2 Studies on the weight status of subjects with ADHD. Case reports, non empirical studies and studies not using standardized ADHD diagnostic criteriawere excluded. (Countinued)

First author Mean age (SD)/age(year) Subjects range (years) Key results Comments

Hubel et al. (2006) 39 boys with ADHD and30 healthy controls

Age range: 8–14 BMI-SDS were higher in ADHDthan in controls. No significantassociation between groupmembership (control vs.ADHD) and obesity oroverweight

Strengths: BMI-SDS wascalculated; exclusion criteria:stimulant treatment, endocrine,metabolic, physical, or otherpsychiatric disorders (exceptconduct disorders)

Anderson et al.(2006)

655 subjects (generalpopulation)

Younger than 16.6 Subjects with ADHD had highermean BMI z-scores at all agescompared with individuals whowere not observed with adisruptive disorder


Limitations: diagnosis of ADHDwas not based on informationfrom third sources; the effect ofcomorbid psychiatric disorders(depression or anxiety) was notcontrolled for

Spencer et al.(2006)

178 children withADHD receivingOROSmethylphenidate

Age range: 6–13 Subjects were slightly overweightcompared with that expectedfor their age (mean BMIz-score = 0.230)


Limitations: the effect ofcomorbid psychiatric disorderswas not controlled for; no dataon the prevalence of obesity oroverweight

Swanson et al.(2006)

140 children withADHD

Age range: 3–5.5 The average BMI was 16.9, whichcorresponds to the 86th

percentile at the baselineassessment

Limitations: the effect ofco-morbid psychiatric disorderswas not controlled for; no dataon the prevalence of obesity oroverweight

Lam and Yang(2007)

1429 students (generalpopulation)

Age range: 13–17 Subjects with high ADHDtendency had an increased riskfor obesity of 1.4 times ascompared to subjects with lowADHD tendency

Strength: large sample sizeLimitations: no formal diagnosis

of ADHD; the effect ofcomorbid psychiatric disorderswas not controlled for

untreated ADHD subjects might have been significantly higherthan controls at baseline. The authors did not report the impactof psychiatric comorbid disorders (such as depressive disorders)on the age- and height-corrected weight index.

Using similar methodology, the same group(Biederman et al., 2003) compared weight and height in asample of 140 ADHD girls and 122 female controls agedbetween 6 and 17 years. The age- and height-corrected weightindex of ADHD subjects was greater than average (althoughnot indicative of overweight or obesity) but no significantdifferences were found between ADHD girls and controls, aswell as between treated and untreated subjects. Interestingly,ADHD girls with comorbid major depression (MD) had asignificantly greater average height- and age-corrected weightindex relative to ADHD girls without MD (with MD, N : 21:126 ± 31.3; without MD, N : 103: 109 ± 25.7; p = .011). Ofnote, the average weight index of the ADHD children withcomorbid MD was greater than the recommended cut-off forobesity (i.e. 120).

In a study conducted in a Child Psychiatry Department,Holtkamp et al. (Holtkamp et al., 2004) found that the meanBMI-SDS of 97 inpatient and outpatient boys (aged 5.5–14.7years), diagnosed with the combined DSM-IV type of ADHD,

was significantly higher than the age-adapted reference valuesof the German population (Kromeyer-Hauschild et al., 2001)(p = 0.038). Moreover, the proportion of obese (7.2%) and over-weight (19.6%) participants (defined as those with a BMI ≥ 97th

and ≥ 90th percentile, respectively), was significantly higherthan the prevalence of obesity and overweight in the Germanpopulation of the same age (p = 0.0008 and p = 0.0075, respec-tively). Of note, exclusion criteria were the use of orexigenicmedications (other than methylphenidate) as well as somatic,neurologic, and psychiatric disorders (such as depression) whichmay have contributed to increase in the prevalence of overweightor obesity. The only psychiatric comorbid disorder was conductdisorder (57.7% of the participants); however, the authors foundno significant differences in the relative number of overweightand obese participants, as well as in the mean BMI standarddeviation scores (SDS), between participants with and withoutconduct disorder. Moreover, although 14.4% of the patients weretreated with methylphenidate (which may have anorexigenic ef-fects) for a mean of five months, there were no significant differ-ences between medicated and medication-free participants. Asstated by the authors, the use of a clinical sample of boys onlyand the lack of control for factors such as socioeconomic statusand BMI of parents represent limitations of the study. Moreover,

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the protocol study did not include a control group: the meanBMI-SDS of the participants was compared to a reference pop-ulation assessed several years earlier, raising the possibility thatthe results may have been due to an isolated trend in increasingobesity. However, Holtkamp et al. (2004) concluded that, aftercomparing recent BMI of the children from the area of the studyto the reference population national norms, this isolated trendwas unlikely.

Curtin et al. (2005) performed a chart review of 98 children(aged 2–19 years) with ADHD (diagnosed according to DSM-IV criteria) in a Child Psychopathology Unit. They found that29% were at risk for overweight (BMI z-scores >85th percentile)and 17.3% were overweight (BMI z-scores >95th percentile); inthe 2–5 year old group, prevalence of at risk for overweight was42.9%. These estimates did not significantly differ in compari-son to an age-matched reference population (NHANES 1999–2002 (Flegal et al., 2002)). However, when the authors analyzedonly the children not treated with stimulants (in order to controlfor the potential anorexigenic effects of these drugs), the preva-lence of at risk for overweight and overweight was, respectively,36% and 23%, differing significantly from that found in treatedparticipants (16% and 6.3%, respectively) (p < 0.05). Interest-ingly, none of the children taking stimulant medications wereunderweight (i.e., below the 15th percentile), although 16% ofthe children not receiving stimulant medications were under-weight. Only small numbers of children with ADHD receivedother types of medications (Selective Serotonin Reuptake In-hibitors (SSRIs) n = 2; anticonvulsants n = 1; antihyperten-sives n = 7; other antidepressants n = 1; and other medicationsn = 5). Unfortunately, because of the small sample size, the au-thors were not able to examine these medications in relation toweight status. Moreover, they could not control for the effect ofpotential comorbid psychiatric disorders.

More recently, Hubel et al. 2006) compared the mean BMI-SDS of 39 boys with ADHD and 30 healthy controls aged 8–14years. All subjects were recruited in the local community. ADHDdiagnoses were made according to the DSM-IV (APA, 1994) cri-teria. Twenty-four ADHD children presented with the combinedtype and 15 with the predominantly hyperactive-impulsive type.None of the participants was taking medications or had takenstimulants in the previous two years. Moreover, none of thesubjects had any endocrine, metabolic, physical, or other psy-chiatric disorders except conduct disorders. It was found that theBMI-SDS were higher in ADHD than in controls (0.29 ± 1.01and 0.05 ± 0.94, respectively). Group differences were morepronounced in older children. No difference was found betweenthe two ADHD groups. Interestingly, the results remained valideven when anxiety/depression symptoms and general psychicimpairments were controlled for. Moreover, the proportions ofobese and overweight subjects in the ADHD group (17.95% and7.69%, respectively) were well comparable to those reported byHoltkamp et al. 2004). However, using chi (APA, 1994) analy-ses, the authors found no significant association between groupmembership (control vs. ADHD) and obesity or overweight.Since differences in weight status between ADHD and control

subjects were more pronounced in adolescence and age effectswere not accounted for in the chi (APA, 1994) analyses, the au-thors could not exclude an actually existing association betweengroup membership and weight status in older subjects.

Anderson et al. (2006) analyzed data from a prospective studyon the determinants and correlates of psychiatric disorders in asample of 655 subjects younger than 16.6 years. Psychiatricdisorders were assessed with a structured diagnostic interviewconsistent with DSM-III-R (APA, 1987) criteria, administeredseparately, by trained lay interviewers, to the parents and the par-ticipants. BMI was calculated from reported weight and height.BMI z-scores were derived using the Centers for Disease Con-trol and Prevention BMI for-age reference (Ogden et al., 2002).Subjects with a disruptive disorder (including ADHD, ODD,and CD) before age 16.6 years had higher mean BMI z-scoresat all ages compared with individuals who were not observedwith a disruptive disorder. Mean BMI z-scores were 0.21 (95%CI, 0.07–0.35) units higher than individuals without a disruptivedisorder. When ADHD, ODD, and CD were modeled separately,the pattern of results did not differ substantially. After exclud-ing subjects using medications, the results did not change. Onelimitation of the study is that the authors did not control forthe effect of potential comorbid disorders such as depressiveor anxiety disorders. Moreover, as discussed for the study byMustillo et al. (2003), given that this was a population survey,diagnoses could not be based on information from third sources(i.e. teachers or other relevant persons).

In another larger population survey, Lam and Yang (2007)investigated the potential association between ADHD and over-weight/obesity in a sample of 1429 students aged between 13and 17 years. Structured interviews according to DSM-IV (APA,1994) criteria were performed for the assessment of ADHDsymptoms. However, given the intrinsic limitations of the studydesign and the number of the participants, structured interviewswere administered to students only and no information was ob-tained from parents or teachers. Therefore, the authors were ableto obtain an “ADHD tendency” more than a clinical diagnosisof ADHD. After adjusting for potential confounding factors in-cluding snoring, it was found that subjects with high ADHDtendency had an increased risk for obesity of 1.4 times as com-pared to subjects with low ADHD tendency. As in other abovediscussed studies, the authors did not control for the effect ofpotential comorbid psychiatric disorders.

Three studies (Faraone et al., 2005; Spencer et al., 2006;Swanson et al., 2006) investigating the growth effects of stimu-lants in ADHD children found, at baseline, a mean BMI z-score>0, indicating that ADHD subjects were heavier than expected.However, these studies did not provide data on the prevalence ofobesity in children with ADHD, as well as of psychiatric comor-bid disorders (such as depressive disorders) which may impactbody mass.

In summary, data from literature indicate that children withADHD have a higher than expected BMI. However, evidencesuggesting an increased prevalence of obesity in subjects withADHD is still limited and inconsistent. Moreover, the impact of

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psychiatric comorbidity on body mass has not been systemati-cally addressed in the above reviewed studies.

Systematic Review: Conclusion

After excluding case reports, descriptive studies with no sta-tistical analyses of data and studies which measured simplesymptoms of ADHD without using diagnostic criteria, empir-ically based evidence suggests that obese patients referred toobesity clinics may present with higher than expected preva-lence of ADHD. Moreover, all reviewed studies indicated thatsubjects with ADHD are heavier than expected. However, dataon the prevalence of obesity in subjects with ADHD are stilllimited. Anyway, even if the comorbidity between ADHD andobesity held true in clinical samples only, it would still haverelevant implications for the clinical presentation and the man-agement of these patients, and so we believe that it is noteworthy.In the next section, we will examine the potential mechanismsthat have been proposed for this possible comorbidity, in orderto better understand the potential implications on the manage-ment of patients with both ADHD and obesity, which will be thesubject of the third section of this review.

POTENTIAL MECHANISMS UNDERLYING THEASSOCIATION BETWEEN ADHD AND OBESITY

Since the above-reviewed studies, pointing to an associationbetween obesity and ADHD, are cross-sectional, they do notallow an understanding of the causality between ADHD andobesity. From a theoretical point of view, we think that the re-sults of our systematic review allow for the consideration ofthe following hypotheses: 1) obesity or factors associated withobesity lead to or manifest as ADHD symptoms; 2) ADHD andobesity are the expression of a common biological dysfunctionthat manifests itself as obesity and ADHD in a subset of patientswho present with both of these conditions; 3) ADHD contributesto obesity.

1) The first hypothesis is that obesity or factors associated withobesity lead to or manifest as ADHD. Recently, Rosval et al.(2006) reported higher rates of motoric impulsiveness in pa-tients with bulimia nervosa and anorexia nervosa binge/purgesubtype in comparison to anorexia nervosa, restricting sub-type and normal eater control group, confirming the previousfindings linking binge eating behaviors with behavioral im-pulsivity (Engel et al., 2005; Nasser et al., 2004). Since bingeeating behaviors may be present in obese patients (especiallyin those with severe obesity) (Hudson et al., 2006), it is pos-sible that impulsivity associated with these abnormal eatingbehaviors contributes to or manifests as impulsivity of ADHDin these patients. It is also possible that impulsivity associatedwith abnormal eating behaviors fosters symptoms of inatten-tion and hyperactivity. Clinicians report that patients with

bulimic or abnormal eating behaviors may present with re-peated and impulsive interruptions of their activities in orderto get food, resulting in ADHD symptoms such as disorga-nization, inattention, and restlessness (Cortese et al., 2007).

Other unexplored hypotheses deserve further investigation.For example, there is some evidence that sleep-disorderedbreathing (SDB) may lead to ADHD or to ADHD symptoms(Chervin et al., 2005). It has been hypothesized that hypoxiaor sleep fragmentation arousals associated with apnea andhypopneas contribute to ADHD. Since obesity is associatedwith SDB (Gami et al., 2003), it is possible that obesity leadsto ADHD/ADHD symptoms via SDB, at least in a subset ofpatients.

2) Another possibility is that obesity and ADHD are differentexpressions of common underlying biological mechanisms.Therefore, ADHD and obesity might share common biolog-ical underpinnings at least in a subset of patients with boththese conditions. Bazar et al. (2006) speculated on some pos-sible common mechanisms, including the “reward deficiencysyndrome.” This syndrome is characterized by an insuffi-cient dopamine-related natural reward that leads to the use of“unnatural” immediate rewards, such as substance use, gam-bling, risk taking, and inappropriate eating. Several lines ofevidence suggest that patients with ADHD may present withbehaviors consistent with the “reward deficiency syndrome”(Gami et al., 2003; Blum et al., 1995, 2000; Heiligensteinand Keeling, 1995). This syndrome has been reported alsoin obese patients with abnormal eating behaviors (Comingsand Blum, 2000). Alterations in the dopamine receptor D2(DRD2) (Bazar et al., 2006) and, to a lesser extent, DRD4(Mitsuyasu et al., 2001; Tsai et al., 2004) have been asso-ciated with the above-mentioned “reward deficiency syn-drome.” Dysfunctions of DRD2 and DRD4 have been foundin obese patients (Noble, 2003; Poston et al., 1998). Sev-eral studies suggest a role of altered DRD4 and DRD2 inADHD as well (although the alteration in DRD2 has notbeen replicated in other studies) (Noble, 2003; Bobb et al.,2005). Therefore, obese patients with abnormal eating be-haviors and ADHD may present with common geneticallydetermined dysfunctions in the dopaminergic system. Inter-estingly, in a study by Levitan et al. (2004) on a sample ofwomen with seasonal affective disorder (SAD), the 7R al-lele of DRD4 was associated with significantly higher scoresof childhood inattention on the WURS-25 and with signif-icantly higher maximal lifetime BMI. SAD is characterizedby marked craving for high-carbohydrate/high-fat foods, re-sulting in significant weight gain during winter depressiveepisodes. A potential implication of the reward system in thepathophysiology of the disorder has been suggested. There-fore, Levitan et al. (2004) hypothesized that childhood atten-tion deficit and adult obesity may be the expression of a com-mon biological dysfunction of the 7R allele of DRD4 asso-ciated with a dopamine dysfunction in prefrontal attentionalareas and brain circuits involved in the reward pathways.

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However, these authors did not consider a formal diagnosisof ADHD according to standardized criteria.

Another potential common biological mechanism involvesalterations in the Brain Derived Neurotropic Factor (BDNF).Preliminary evidence from animal model studies points toa potential dysfunction of BDNF underlying both ADHDand obesity (Lyons et al., 1999; Kernie et al., 2000; Rios etal., 2001). However, a recent study by Friedel et al. (2005)in humans does not suggest a large role of genetic varia-tion of BDNF in ADHD and obesity. On the other hand,recently Gray et al. (2006) found a functional loss of onecopy of the BDNF gene in an 8-year old with hyperphagia,severe obesity, impaired cognitive function, and hyperactiv-ity. Therefore, given the limited and inconsistent findings, therole of common genetic mutations underlying shared neuro-biological dysfunctions in ADHD and obesity deserves fur-ther investigation. Clearly, a bidirectional rather than uni-directional relationship between obesity and ADHD wouldsuggest stronger evidence for common mechanisms betweenthe two.

3) Our systematic review indicates that subjects with ADHDpresent with higher than expected body mass. This may sup-port the hypothesis that ADHD actually contributes to obe-sity. Abnormal eating behaviors associated with ADHD mayplay a significant role. Altfas (2002) reported that, in his ex-perience, impulsive eating behaviors are common in adultand adolescent patients with both ADHD and obesity. Ac-cording to clinical observations of Curtin et al. (2005), chil-dren with ADHD may be at increased risk for overweightdue to their unusual dietary patterns. In a study (Mattos etal., 2004) of a clinical sample of 86 Brazilian adult patientswith ADHD (DSM-IV (APA, 1994) criteria), the prevalenceof Binge Eating Disorder was 8.13%, which is higher thanthe estimate in the general population (2.6%). The authorscorrectly point out that, since only two DSM-IV criteria forBED involve impulsivity or its correlates, ADHD impulsivityper se would not be enough for a BED diagnosis, suggestinga true comorbidity. However, only two participants with BEDwere overweight and none were obese. This, according to theauthors, is atypical, since, as they stated, “although weightis not part of BED criteria, this is a very common feature.”In a study on 110 adult healthy women (age range: 25–46years), Davis et al. (2006), using structural equation mod-elling, found that ADHD symptoms and impulsivity weresignificantly correlated with abnormal eating behaviors, in-cluding binge eating and emotionally-induced eating, which,in turn, were positively associated with BMI. In a recent anal-ysis of 4 case-controls studies, Surman et al. (2006) foundsignificantly greater rates of bulimia nervosa in women withversus without ADHD, but not in men or children; however,the mean BMI of the patients with bulimia was not reportedin this paper. In another recent study of a clinical sample of99 severely obese adolescents (aged 12–17 years), Corteseet al. (2007) found that, after controlling for potentially con-

founding depressive and anxiety symptoms, ADHD symp-toms, measured by the ADHD-index score of the ConnersParents Rating Scale (CPRS) (Conners, 1969), were signifi-cantly associated with bulimic behaviors.

At the present time, it is not clear which dimension ofADHD (inattention, hyperactivity, or impulsivity) may specifi-cally be associated with abnormal eating behaviors. The resultsof Cortese et al. (2007), i.e. significant association between bu-limic behaviors and ADHD-index score (which measures symp-toms of inattention, impulsivity, and hyperactivity) and lack ofsignificant association between bulimic behaviors and CPRS-hyperactivity-impulsivity index (which contains only one itemof impulsivity) led the authors to speculate that both a) impul-sivity and b) inattention might lead or contribute to abnormaleating behaviors, whereas hyperactivity would not play a signif-icant role.

a) As for impulsivity, Davis et al. (2006) suggested that bothdeficient inhibitory control and delay aversion, which areexpression of the impulsivity component of ADHD, mayfoster abnormal eating behaviors, which, interestingly, corre-lated to patients’ BMI in their study. Deficient inhibitory con-trol, which manifests itself as poor planning and a difficultyto monitor one’s behavior effectively, could lead to over-consumption when not hungry associated with the relativeabsence of concern for daily caloric intake. A strong delayaversion could favor the tendency to eat high caloric content“fast food” in preference to less caloric content home-cookedmeals (which take longer to prepare). This may contribute tomaintain a chronic positive energy balance, associated withobesity. Interestingly, several studies showed that obese sub-jects employ less effective strategies than non obese subjectson delay gratification tasks (especially with edible incentive)(Bonato and Boland, 1983; Bourget and White, 1984; John-son et al., 1978; Sigal and Adler, 1976). This might contributeto overweight.

b) It is also possible that inattention and deficits in executivefunctions (which, as stated in the introduction, are frequentlyassociated with ADHD), cause difficulties in adhering to aregular eating pattern, favoring abnormal eating behaviors.Davis et al. (2006) pointed out that patients with ADHDmay be relatively inattentive to internal signs of hunger andsatiety. Therefore, they may forget about eating when theyare engaged in interesting activities and they may be morelikely to eat when less stimulated, at which point they may bevery hungry. In the study of Altfas (2002), all obese partic-ipants with ADHD were diagnosed with the predominantlyinattentive type of ADHD and they had more difficulty los-ing weight, despite a significantly higher number of visits,and a trend toward a longer duration of treatment than nonADHD patients. This kind of inefficiency (“taking more timeto accomplish less”) may be linked to attentional and organi-zational difficulties. In line with this hypothesis, two recentstudies (Beutel et al., 2006; Gunstad et al., 2007) reported

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poorer executive function test performance in obese vs. nor-mal weight subjects.

Another explication on the association between inattentionand obesity was provided by Schweickert et al. (1997). Accord-ing to these authors, compulsive eating may be a compensatorymechanism to help the person control the frustration associatedwith attentional and organizational difficulties. Finally, Levitanet al. (2004) hypothesized that difficulties initiating activitieslinked to attentional and organizational difficulties contribute todecreased caloric expenditure, leading to weight gain over time.

One can not exclude that all of the three above hypothesesmay hold true and may co-exist, at least in certain subjects.

MANAGEMENT OF PATIENTS WITH ADHDAND OBESITY

From a clinical standpoint, the results of our systematic re-view suggest that it may be useful 1) to screen for ADHD inpatients with obesity and 2) to look for abnormal eating behav-iors in patients with ADHD.

1) As pointed out by Agranat-Meged et al. (2005), obesity maymask hyperactivity since “obese individuals are less mobile.”Therefore, clinicians may overlook the need of looking atADHD in obese patients. However, screening for ADHD inpatients with obesity may be of relevance for two reasons.First, as Altfas (2002) first noted, obese patients with ADHDmay have difficulties in weight loss. Therefore, the manage-ment of ADHD might improve the management of obesityitself. Second, screening for and treating ADHD in obesepatients, independently from associated abnormal eating be-haviors, is relevant in light of the personal and social bur-den that ADHD adds to the already impairing condition ofobesity.

2) Well known comorbid psychiatric disorders, such as anxietyor conduct disorders, are frequently investigated in clinicalpractice with ADHD patients. Recent works (Mattos et al.,2004; Surman et al., 2006) suggest that abnormal eating be-haviors such as BED and bulimia, which are generally poorlyinvestigated in patients with ADHD, should be screened aswell. These abnormal eating behaviors may further impactthe quality of life of these patients and might contribute toobesity.

Therefore, the subset of obese patients with abnormal eatingbehaviors and ADHD should be considered a group particularlyat risk and meritorious of appropriate management.

With regard to the therapeutic strategies, if the hypothesis thatADHD actually contributes to obesity is true, then the treatmentof ADHD might improve obesity. Several reports (Schweick-ert et al., 1997; Sokol et al., 1999) have suggested that stimu-lants improve ADHD and abnormal eating behaviors in patients

with both conditions. Surman et al. (2006) explained the find-ings of these reports suggesting that the treatment of ADHD-related impulsivity could improve abnormal eating behaviors.Improvement in attention, leading to more regular eating pat-terns, may also play a significant role. However, none of thesereports specifically analyzed obese participants, so evidence thatimprovements in eating behaviors due to ADHD treatment leadto a weight loss in obese patients with ADHD is still missing.

Indeed, these reports also support the hypothesis that ADHDand abnormal eating behaviors share common underlying bio-logical mechanisms, which may be the target of ADHD medi-cations, or that ADHD medications act both on the brain path-ways involved in ADHD and on those that mediate abnormaleating behaviors. Meredith et al. (2002) found that repeatedinjections of amphetamine were accompanied by an elevatedBDNF mRNA and BDNF immunoreactivity in the basolateralamygdala, rostral piriform cortex, and paraventricular nucleusof the hypothalamus. Since there is some evidence that reduc-tion of BDNF in the hypothalamus causes increased locomotoractivity and eating behaviors (Kernie et al., 2000), the findingof Merendith et al. (2002) supports the hypothesis that ADHDmedications may also act on brain pathways involved in eatingbehaviors. Moreover, Gadde et al. (2006) published a trial on theefficacy of atomoxetine, the second-line medication of ADHD,in weight reduction in obese women. The positive results of thetrial suggested that this ADHD drug may act on the noradren-ergic synapses in the medial and paraventricular hypothalamusthat are thought to play a major role in modulating satiety andfeeding behavior.

These preliminary observations suggests that in patients withADHD and abnormal eating behaviors (associated with obesity),both conditions might improve using the same class of agents.This is particular important considering that other agents (SSRIs,which are not highly effective in patients with ADHD) repre-sent the usual pharmacological treatment for abnormal eatingdisorders.

To our knowledge, at the present time, there are no con-trolled studies on the impact of non- pharmacological treatmentof ADHD on weight reduction. Since it is possible that an im-provement in the attentional and organizational strategies leadsto a decrease in abnormal eating behaviors resulting in a weightloss, research in this field should be particularly encouraged, aswell as studies assessing the effectiveness of the combination ofpharmacological and non-pharmacological treatment of ADHDon weight loss in obese patients.

On the other hand, we are not aware of any studies assessingthe impact of the treatment of binge eating on ADHD symptomsin patients with ADHD and abnormal eating behaviors. We thinkthat such studies should be encouraged.

CONCLUSION

Clinicians have generally overlooked the potential associa-tion between ADHD and obesity, possibly because hyperactiv-ity (the most evident but not necessarily the most significant

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symptom of ADHD) may be masked by obesity. However, em-pirically based evidence from recent literature points to a possi-ble comorbidity between ADHD and obesity, at least in clinicalsamples of obese patients. Data on the prevalence of obesity inADHD patients are still limited. More methodologically soundstudies, using standardized diagnoses of ADHD and homoge-neous definitions of obesity/overweight, as well as controllingfor potential confounding factors (such as socioeconomic sta-tus) and psychiatric comorbid disorders (such as depressive andanxiety disorders) are greatly needed. However, even if the as-sociation between ADHD and obesity held true only in obesepatients treated in specialized clinics, it would still be notewor-thy since this is the class having the highest mortality and mor-bidity risk and the greatest need for effective treatment. Giventhat the management of ADHD might improve eating behaviors,screening for ADHD in these patients may be of clinical rele-vance. Since it has been shown that reduction of body weight assmall as 5% substantially reduces the morbidity and mortalityrisks of obesity (Altfas, 2002), even if ADHD only modestlyimpacted weight status, such screening may be relevant. On theother hand, screening for overlooked abnormal eating behaviorsmay improve the symptoms and the quality of life of patientswith ADHD and may potentially prevent weight gain whichwould add a further burden to these patients.

Prospective studies, at present still lacking, could lead to abetter understanding of the causality in the relationship betweenADHD and obesity, shading light into the psychopathologicalpathways linking the two conditions.

Family studies examining the occurrence of ADHD and obe-sity and further animal model studies are necessary to gain in-sight into the potential common genetic underpinnings.

Finally, pharmacological and non-pharmacological treatmentstudies are greatly needed to find more appropriate and effectivetherapeutic strategies for patients with both obesity and ADHD.

Therefore, clinical empirically based studies, epidemiologi-cal surveys (both cross-sectional and prospective), genetic stud-ies, animal model studies, non-pharmacological treatment stud-ies, and pharmacological trials should be highly encouragedsince they may advance the knowledge in the field, allowingfor better management, and ultimately, a better quality of lifefor patients with both obesity and ADHD.

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Cortese Et Al 2008-Critical Reviews in Food Science

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