The Fat-Soluble Vitamins (A, D, E, and K)

Vitamin A (Retinol) Foods from animal source provide various retinoids that are easily converted to

retinol in the body Foods from plant source provide carotenoids Over 500 carotenoids are found in nature Less than 10% with provitamin A activity b-carotene highest activity Must be acted upon in the gut or by the liver to form retinol

Sources of Vitamin A Animal sources

Liver Milk

Egg yolk

Plant sources Alfalfa Green leafy vegetables

The Retinoids 3 forms of vitamin A important for health

Retinal Retinoic acid Retinol (key player; can be converted to other forms)

β-carotene (a carotenoid or pigment) in yellow/orange foods is a potent provitamin A

Carotenoid Cleavage and Storage β-carotene is converted to vitamin A in the intestinal mucosa 90% is stored in liver, mainly as the ester, retinyl palmitate (~ 6 months storage)

Small amounts in adipose and blood Carotenoids can be stored in adipose tissue Retinol binding protein acts to transport vitamin A from the liver and in the blood

Carotenoids Additional physiologic effects beyond

vitamin A Antioxidant

Remove excess “electrons” from cell system

Electrons (free radicals) damage cells and DNA

Vitamin A Roles in the Body Promote vision (retinal) Participate in protein synthesis and

cell differentiation Support reproduction and growth Support immunity (retinoic acid and

carotenoids) Involved in bone growth and

remodeling Synthesis of glycoproteins Antioxidant activity (β-carotene)

Immune Functions Carotenoids

Lycopene, b-carotene Serve as antioxidants

Antibody response to infections

Vitamin A – Deficiency Night blindness

Leading cause of blindness in third world countries

Cell keratinization Dry skin Xerophthalmia (dryness of cornea & conjunctiva)

Reproductive failure Abnormal skeletal development/maintenance Immune dysfunction

Vitamin A Toxicity Skeletal malformations, spontaneous fractures, internal hemorrhages Overconsumption of beta carotene from food sources may cause skin to turn yellow but

is not harmful Birth defects and miscarriage Decalcification, joint pain, fragility Dry itchy skin (caution about acne treatments) Hair loss Liver damage

Vitamin D (The Sunshine Vitamin) Body can make it if exposed to enough sunlight Made from cholesterol in the skin Vitamin D = calciferol Vitamin D2 = ergocalciferol

Completely synthetic form produced by the irradiation of the plant steroid ergosterol

Vitamin D3 = cholecalciferol Produced photochemically by the

action of sunlight or ultraviolet light from the precursor sterol 7-dehydrocholesterol

Vitamin D – Sources Not found naturally in many foods Synthesized in body Plants (ergosterol) Fluid milk products are fortified with vitamin D Oily fish Egg yolk Butter Liver Difficult for vegetarians

Vitamin D – Functions Bone development

Calcium absorption (small intestine) Calcium resorption (bone and kidney) Maintain blood calcium levels Phosphorus absorption (small intestine)

Hormone Regulation of gene expression Cell growth

Vitamin D – Deficiency Children

Rickets Failure of bones to grow properly Results in “bowed” legs or knock-knees,

outward bowed chest and knobs on ribs Adults

Osteomalacia: Adult form of rickets Softening of bones, bending of spine, and

bowing of legs Osteoporosis (porous bones):

Vitamin D plays a major role along with calcium

Loss of vitamin D activity with advancing age

Associated with fractures à very serious for geriatrics

Vitamin D Toxicity Calcification of soft tissue

Lungs, heart, blood vessels Hardening of arteries (calcification)

Hypercalcemia Lack of appetite Excessive thirst and urination

Osteomalacia

Normal Pelvis

Vitamin E (Tocopherol) Alpha-tocopherol is most active form Vitamin E is very unstable

Vitamin E – Sources Plant sources

Cereal grains (Especially in germ) Vegetable and seed oils

Little in animal sources Beef fed high levels of vitamin E right before slaughter to improve shelf life can

be source

Vitamin E – Functions Antioxidant

Free radical scavenger Protects: cell membranes, LDL from oxidation, and double bonds in

polyunsaturated fatty acids Prevention of rancidity Works in conjunction with selenium

Protects: lungs from pollutants, DNA, and heart

Vitamin E – Deficiency Rare – typically associated with fat malabsorption or excessive intake of

polyunsaturated fatty acids (PUFAs) Erythrocyte hemolysis and hemolytic anemia Prolonged deficiency causes neuromuscular dysfunction; affects the spinal cord

and the retina

Vitamin E – Deficiency Reproductive failure

Embryonic degeneration Ovarian failure Testes degeneration Fetal resorption

Derangement of cell permeability Liver, brain, kidney, or blood capillaries

Muscular lesions Failure to growth, unthriftiness

Vitamin E Toxicity Vit. E toxicity is rare

Extreme high doses (50- to 100-fold above recommended intakes) may affect the blood clotting effects of vitamin K and may lead to increased risk of hemorrhage

Vitamin K (The Clotting Vitamin) Dicoumarol and warfarin are antagonists of vitamin K Dicoumarol found in moldy sweet clover Warfarin

Rat Poison

Vitamin K – Sources Bacteria in the large intestine (10-15%) or rumen Plant sources

Green leafy vegetables Some oils Broccoli

Animal sources Liver Milk

Forms of Vitamin K K1, phylloquinone

Chloroplasts in plants K2, menaquinone

Bacterial synthesis K3, menadione

Synthetic, water soluble form Complexed to improve stability

Functions of Vitamin K Clotting factors are synthesized in the liver as

inactive precursors - vitamin K converts them to their active forms

Conversion of prothrombin to thrombin, an active enzyme

Formation of fibrinogen to fibrin, leading to clot formation Stimulates bone formation and decreases bone resorption

Vitamin K – Deficiency Primary deficiency rare; secondary deficiency occurs

when fat absorption is impaired (e.g., cystic fibrosis, Crohn’s disease) or following long-term or high-dose administration of antibiotics (they kill the bacteria in large intestine)

Newborn babies with sterile GI tract; single vitamin K dose given to prevent hemorrhage

Generalized hemorrhages (Prolonged clotting time)

Vitamin K – Toxicity Not common except with over-supplementation

Phylloquinone and menaquinone are relatively nontoxic Jaundice; brain damage

Menadione toxic to skin and respiratory tract in high doses