2009 Cengage-Wadsworth Chapter 10 The Fat-Soluble Vitamins.

2009 Cengage-Wadsworth

Chapter 10

The Fat-Soluble Vitamins


Vitamin A & Carotenoids

• Sources– Retinoids - liver, dairy, fish– Carotenoids - brightly colored fruits &

vegetables-carotene - greatest provitamin A

activity



• Digestion & absorption– Vitamin A requires digestion

• Retinol bound to fatty acid esters• Retinyl esters & carotenes often

complexed with protein

– Emulsification of fat globules– Retinol absorbed via protein carrier– Carotenoids absorbed via

transporters & passive diffusion



– Carotenoids & retinoids metabolized in enterocytes to some extent

– Retinol esterified & incorporated into chylomicrons for transport• Cellular retinol-binding protein (CRBP) II

• Transport, metabolism, & storage– Chylomicrons carry to liver– Additional metabolism in liver



– Retinol that is esterified may be stored in the liver• Stellate cells & parenchymal cells

– Transported in blood via 2 proteins• Retinol-binding protein (RBP)• Tranthyretin (TTR)

– Carotenoids transported as part of lipoproteins

– Carotenoids stored in liver & adipose



• Functions & mechanisms of action– Vitamin A

• Vision - rhodopsin• Cellular differentiation• Gene expression• Growth• Other functions - reproduction, bone

metabolism



– Carotenoids• Antioxidant functions

– Carotenoids & eye health– Carotenoids & heart disease

• Cell proliferation, growth, & differentiation

– Carotenoids & cancer– Carotenoids & health claims



• Interactions with other nutrients– Vitamins E & K– Protein & zinc– Iron

• Metabolism & excretion– Retinol is oxidized & conjugated to make

polar, water-soluble metabolites– Excreted in urine (60%), lungs, feces– Carotenoids metabolized to variety of

compounds & excreted into bile



• Recommended Dietary Allowance– 1 RAE = 1 µg retinol = 12 µg -

carotene = 24 µg -carotene or -cryptoxanthin

– Men: 900 µg RAE; women: 700 µg RAE

– Pregnancy: 770 µg RAE; lactation: 1,300 µg RAE

– UL = 3,000 µg RAE



• Deficiency– Xerophthalmia, keratinization

• Toxicity: hypervitaminosis A• Assessment of nutriture

– Conjunctival impression cytology (CIC)– Plasma retinol concentrations– Relative dose response (RDR) test or

modified RDR test


Vitamin D

• Sources– Liver, beef, veal, eggs, dairy, some

saltwater fish– Synthesis in skin

• Absorption, transport, & storage– Dietary D absorbed in micelle– Incorporated into chylomicron for

transport


Vitamin D

– Cholecalciferol diffuses from skin into blood & picked up by vitamin D-binding protein (DBP) for transport

– Metabolized to 25-OH D3 in liver– 25-OH D3 secreted into blood,

transported by DBP– Kidneys convert to 1,25-(OH)2 D3

(calcitriol)– Calcitriol trasported in blood via DBP


Vitamin D

• Functions & mechanisms of action– Calcium homeostasis

• Calcitriol & the intestine• Calcitriol & the kidney• Calcitriol, 24R,25-(OH)2 D3, & the bone

– Cell differentiation, proliferation, & growth

– Other roles - BP, autoimmune disorders, insulin secretion


Vitamin D

• Interactions with other nutrients– Calcium, phosphorus, vitamin K

• Metabolism & excretion– Metabolites excreted in feces (>70%) &

urine

• Adequate Intake (may be inadequate)– 6 mo-50 years: 5 µg or 200 IU– 51-70 years: 10 µg (400 IU); >70: 15 µg

(600 IU)


Vitamin D

• Deficiency: rickets & osteomalacia– Rickets - children: seizures, growth

retardation, bones don’t mineralize– Osteomalacia - adults: bone mineralization

defects

• Toxicity– UL = 50 µg (2,000 IU)

• Assessment of nutriture– Plasma concentration of 25-OH D3


Vitamin E

• Sources– Plant oils (canola, olive, sunflower,

safflower, cottonseed), whole grains, legumes, some fruits & vegetables

– High-fat meats (inferior)


Vitamin E

• Digestion, absorption, transport, & storage– Tocotrienols hydrolyzed; synthetic

ester forms digested– Absorbed primarily in jejunum by non-

saturable, passive diffusion– Chylomicrons for transport– Liver recirculates some in VLDL– Stored mostly in adipose tissues


Vitamin E

• Functions & mechanisms of action– Antioxidant role

• Free radical termination• Singlet molecular oxygen destruction

– Other roles• Vitamin E & heart disease• Vitamin E & eye health• Other conditions


Vitamin E

• Interactions with other nutrients– Selenium, vitamin C– Sulfur-containing AAs – Polyunsaturated FAs

• Metabolism & excretion– Several metabolites excreted in urine– Major route is feces via bile


Vitamin E

• Recommended Dietary Allowance– Adults (including pregnancy): 15 mg -

tocopherol– Lactation: 19 mg -tocopherol

• Deficiency• Toxicity

– UL = 1,000 mg -tocopherol

• Assessment of nutriture– Plasma concentrations– Erythrocyte hemolysis test


Vitamin K

• Sources– Leafy green vegetables, legumes– Bacterial synthesis

• Absorption, transport, & storage– Phylloquinone absorbed in small

intestine in micelles– Menaquinones absorbed by passive

diffusion from ileum & colon


Vitamin K

– Transported in chylomicrons, LDL– Stored in liver & other tissues

• Functions & mechanisms of action– Vitamin K & blood clotting

• Overview of blood clotting• The role of vitamin K in carboxylation of

glutamic acid residues

– Vitamin K & bone & nonosseous tissue proteins


Vitamin K

• Interactions with other nutrients– Vitamins A & E– Vitamins D & A

• Metabolism & excretion– Phylloquinone metabolites excreted

primarily in feces & in urine– Menaquinone thought to be

metabolized & excreted in bile & urine


Vitamin K

• Adequate Intake– Men: 120 µg; women: 90 µg

• Deficiency– Newborns, malabsorption, antibiotics

• Toxicity - synthetic menadione• Assessment of nutriture

– Plasma or serum phylloquinone– Blood clotting or prothrombin time– Undercarboxylated vitamin K-dependent

proteins


Perspective 10

The Antioxidant Nutrients, Reactive Species, & Disease


Antioxidant Nutrients

• Free radical chemistry• Generation of reactive species

– The superoxide radical– Hydrogen peroxide– The hydroxyl radical– Peroxyl, hydroperoxyl, & carbon-

centered radicals & lipid peroxides



– Singlet molecular oxygen– Nitric oxide– Peroxynitrite– Nitrogen dioxide & peroxynitrate

• Damage due to reactive species• Antioxidant nutrient functions

– Elimination of superoxide radicals



– Elimination of hydrogen peroxide– Elimination of hydroxyl radicals– Elimination of peroxyl, hydroperoxyl,

& carbon-centered radicals, & lipid peroxides

– Elimination of singlet molecular oxygen



• Regeneration of antioxidants– Vitamin E regeneration

– Ubiquinol (coenzyme QH2) & thioredoxin regeneration

– Glutathione regeneration– Vitamin C regeneration

• Antioxidants & disease

2009 Cengage-Wadsworth Chapter 10 The Fat-Soluble Vitamins.

Documents

Transcript of 2009 Cengage-Wadsworth Chapter 10 The Fat-Soluble Vitamins.