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
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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)
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
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