ASSESSING HEALTH REQUIREMENTS

AND

SETTING DIETARY STANDARDS

FOR MINERALS

Evaluating Individual Need Evaluating Individual Status

Setting Standards for optima

Experimental

Balance Studies Biomarkers Functional tests

Population Approach

NUTRITIONAL CONCERNS

Assessing Mineral Status

Major Categories to Consider and Attack

Body stores of the mineral

Functional indices

Response to increase intake

Caution: Seldom can one mineral be evaluated by all three. Choice of most favorable will depend on the mineral being assessed.

EAR(50%)

RNI (97.5%) UL (0%)

Acceptable range of intake Acceptable range of intake

Risk ofdeficit

Risk ofdeficit

Risk ofexcess

Risk ofexcess

0.5

1.0

Intake

How are data that generates this curve obtained?How are data that generates this curve obtained?

Cumulative Risk

LOAEL

EAR: Estimated Average Requirement

UL: upper limit

RNI: Recommended nutrient intake

LOAEL: Lowest observed adverse effect level

NOAEL: No observed adverse effect level

NOAEL

Question: How does one assess mineral status?

1. Balance studies

2. Clinical observations

Question: How do we estimate safe mineral intake?

3. Optimal intake

5. Sub-clinical evaluations

Approaches

4. Evidence-based approaches

Balance Approach (keeping the status quo)

Choice of endpoint dubious

Matching input with excretion

Overlooks prior exposure and system adaptation

Choice of time may be critical

Maintain body stores

Recover loss due to metabolic turnover

Problems:

Assess the ability of the system to:

Delay appearance of clinical signs

BalanceMatching what goes in with what goes out

A B DKin

Kout

Absorption Excretion

C

K1 K-1 Retention

Kin Kout= Balance

Kin Kout> Positive Balance (growth)

Kin Kout< Negative Balance (wasting)

Absorption-Excretion

K1 K-1=

K1 K-1

K1 K-1<

>

Balance

Positive Balance

Negative Balance

Retention

Problems With Balance as a Criterion of Amount

1. End Point is in doubt

2. Excretion is episodic not continuous

3. Multiple connecting pools of the same mineral

4. System adaptation

Clinical Approach:

Look for or create a disease state

Look for a structural or functional abnormality

Link these with known biochemical or functional changes

Parameters:

Growth rate

Physical appearance (skin, bone, hair, etc.)

Cognitive functions

Biochemical impairments (stress factors, enzymes and metabolic factors)

Physiological impairments (gastrointestinal, immune and nervous system)

Medical (proneness towards disease)

Optimal Intake Approach for Assessing Requirement

Specific nutrient requirement of minerals is that which:

Compare with an accepted standard

1. Optimal mineral nutrition of milk should duplicate the composition of human milk.

Example:

1. Optimize physical or mental performance2. Thwarts or reverses disease3. Increase longevity

Problems:

1. Too general2. Defies population-based approaches

Evidence Based Approach

Evaluate studies pro and con and weigh strengths, weaknesses, design differences, etc. in arriving at a set of numbers

More a propos to setting dietary risk standards than determining requirements:

Sub-clinical (Functional) Approach

Biomarkers of adequacy and deficiency

An ideal biomarker is some reliable internal factor that

responds directly, specifically, and

quantitatively to changes in a mineral’s homeostasis

Its function is to signal a disturbance in the

functional stores of a mineral

The most common signal elicited is a

depression in blood or tissue levels of the

mineral

Body stores of the mineral

Applies mainly to iron

Circulating levels of ferritin are a measure of iron tissue stores

Total iron binding capacity (TIBC)

Transferrin saturation

Hematocrit

Hemoglobin levels

Red cell morphology

Functional indices

Inadequate intake of some minerals causes major perturbations in biochemistry. This is most noted by depressed levels of enzymes, homones, or altered tissue morphology.

Its imperative that a direct connection exist between the mineral in question and the functional component.

Examples

Iodine deficiency circulating thyroid hormone

Copper deficiencyplasma ceruloplasmin

Suspect Measure

Selenium deficiency glutathione peroxidase

Organs and Systems that Play a Major Role in Mineral Homeostasis

Mineral Absorption Endogneous excretion Kidneys

Gastrointestinal tract

Iron Single major site --- ---

Copper Substantial Major (liver) ---

Manganese Major Major (liver) ---

Zinc Major Major ---

Iodide Major

Selenium (After Hambidge, 2003) Major

Chromium Major

Molybdenum Major

Assessment of Iron

Plasma - 4 mg (0.08-0.1%)

Absorption 0.5 -2 mg

Enzymes 5 mg

Myoglobin 200 mg

Excretion 1-2 mg

Storage 1,500 mg

Erythrocytes 2.5 grams

4-5 grams of iron

Liver, spleen, bone marrowone-third

Myoglobin,mitochondria -one third

Two-thirds

10 -14 mg ingested

Ferritin

Measurement of Iron status• Transferrin saturation

– TIBC (total iron binding capacity)– UIBC (unsaturated iron binding capacity)– 33% saturated normally– 47% in the morning (after fasting)– 13% at night

• TIBC = 400 ug/dl …..deficient– = 200 ug/dl…..inflammation

Test is performed when there is concern for anemia, iron deficiency, or iron deficiency anemia

TIBC = Iron binding capacity of a volume of serum (dL)

Expressed as ug of iron needed to fill all Tf molecules in that volume

Determined spectrophotometrically

UIBC = total iron in a volume of serum / TIBC for that volume

Expressed as percentage of saturated transferrin

Determined by atomic absorption analysis of iron in serum

UIBC first determines how much iron is present in a serum sample. 99% of that iron is bound to transferrin. TIBC says how much iron is needed to fill all vacancies on the transferrin in that volume of serum. Comparing how much is there to how much is need to fill vacancies measures percent saturation

Meaning of Terms

Fe-Tf complex

Fe

Draw Blood Serum

Saturation

Fe3+

The amount of Fe3+ required to reach saturation of all the transferrin present

is a measure of the total iron binding capacity (TIBC)

Blood Cells

Change in color due to more Tf becoming saturated with iron

Measuring TIBC

Centrifuge

Sample Problem

An clinical lab draws 5 ml of blood to determine the TIBC and UIBC of a patient. 2 ml of the serum from the blood requires 12 ug of iron to reach saturation. That same serum contains 4.7 ug of iron per ml. Calculate the patients TIBC? UIBC? What can you conclude about the patients iron status?

SolutionTIBC is expressed in deciliters (dL) of blood. One deciliter = 100 mL

If 2 ml requires 12 ugm of iron, 100 mL requires 50 x 12 = 600 ugm

TIBC = 600 ugm/dL

UIBC is expressed as percent of saturation

If 4.7 ugm is present in 2 mL, 100 mL contains 50 x 4.7 = 235 ugm

UIBC = 235/600 x 100 = 39% saturatedWithin NORMAL range

39% 61%

(Note: Knowing the exact amount of Tf is unnecessary)

1. Most sensitive indicator of iron stores

Ferritin (major iron storage protein)

1 g ferritin/L plasma = 8 mg stored iron (Bothwell et al, 1979)<12 ng ferritin/L plasma = no iron stores

Adults

Children

1 g ferritin/L plasma = 14 mg stored

National Surveys

Percentile Men (19-30) Women (19-30) Children

5th 36 7 6

50th 112 36 23

99th 394 212 116

( g ferritin/L plasma)

Problems with Ferritin

An Acute phase protein that is elevated in:

inflammations

infections

disease (neoplasms especially of the colon, cardiovascular)

ethanol consumption

hyperglycemia

body mass index

New Frontiers with Iron

Soluble transferrin receptor concentration of the plasma (a good index of early iron deficiency)

Basis of analysis

Cells requiring iron express transferrin receptors

Extracellular domain or the receptors is subject to proteolytic cleavage and released into plasma

Number of receptors is in proportion to the number that were expressed on the cell surface…which measures iron requirement

Assessment of Zn

Clinical Evaluation of Zinc Adequacy

Before and After Zn Therapy

Problem: Assume you are a physician who specializes in mineral deficiencies. A patient is referred to you by his physician who suspects a zinc deficiency. How can you confirm the diagnosis?

Give the pros and cons for each of the following

1. Measure serum zinc levels

2. Measure 24 hr urine zinc excretion

3. Measure fecal zinc excretion

4. Measure lymphocyte zinc content

5. Measure zinc in hair

6. Measure liver zinc

7. Measure activity of a zinc-dependent enzyme

8. Measure metallothionein levels of blood or mRNA in monocytes

The above scenario also applies to a veterinarian who

is attempting to determine the reason for stunted growth in livestock and

suspects zinc deficiency as the cause

9. Measure body pools of zinc with radioactive tracer

Zinc (a major trouble mineral for biomarkers)

Problems with Zinc:

1. Zn deficiency can be manifested by slight decrements in tissue Zn. An impairment can occur before a change is detected.

2. Internal Zn changes are immediately corrected by a very effective homeostatic mechanism. Thus a biomarker may never be turned on

3. Zinc’s usage is so wide-spread and interconnected that to focus on any one factor is not always practical.

4. Plasma contains only about 0.1% of the body Zn, questioning whether plasma Zn changes reflect total body Zn. Nonetheless, plasma Zn is currently the most widely used and accepted biomarker of Zn status.

5. Plasma Zn is depressed whenever an acute phase response is triggered

6. Plasma Zn tends to be down in hypoalbuminemia

Experimental Observations:

1. No correlation was found between intake/absorption and plasma Zn levels over a wide range of dietary Zn in adult women (Sian et al, 1996). But, dietary and absorbed Zn was found to correlate with dynamic Zn pool size (Sian et al, 1996; Krebs et al, 2000).

Comment: Evidence for a rapid self-correcting homeostatic mechanism?

2. Young children with a Zn-limiting growth impairment have plasma Zn levels within the normal range (Wada et al, 1985)

3. Low plasma Zn levels (<70 ug/L) are a good predictor of growth response to oral Zn supplementation.

IS PLASMA ZINC THE BEST INDICATOR OF ZINC STATUS

OTHER ZINC INDICATORS

1. Cellular components (carbonic anhydrase). The major erythrocyte pool of zinc. But,

1. Does not turnover2. Membrane-bound Zn also a factor 3. applies also to monocyte, neutrophil, and platelet Zn

2. Hair Zn. Good marker. But,1. More relevant to chronic as opposed to transient Zn status

3. Zinc Excretion (urine and feces)1. Requires tracers and metabolic collection2. More applicable to research than clinic screening

4. Tissue stores1. Also requires tracer and sample collection over many days2. Metallothionein mRNA (PCR) in monocytes promising

OTHER ZINC (cont.)

5. Zinc-dependent enzymes. Suppression of the following is inconsistent1. Alkaline phosphatase2. CuZn superoxide dismutase3. lymphocyte 5’-nucleotidase

6. Response to Zn supplementation1. Dietary levels was also be taken into account2. Response to Zn must be specific and non-pharmacological