Fat-Soluble Vitamins Overview

Study Notes

Vitamins are essential nutrients needed in small amounts to prevent deficiency diseases and promote health.
Bioavailability is the rate and extent a nutrient is absorbed and used in the body.
Precursors (provitamins) are inactive forms of vitamins that become active in the body.
Vitamins are organic and can be destroyed by cooking and storage.

Water-soluble vitamins are absorbed directly into the blood, circulate freely in the body's water-filled areas, and are excreted by the kidneys.
Fat-soluble vitamins are absorbed into the lymph first, then the blood, often requiring protein carriers. They are stored in fat-associated cells and are less readily excreted.

Vitamin A exists in the body as retinoids: retinol, retinal, and retinoic acid.
Sources include: retinyl esters (animal foods) and beta-carotene (plant foods).
In the body, retinol supports reproduction and retinal participates in vision. Retinoic acid regulates growth.
Functional roles: promoting vision, maintaining the cornea, and conversion of light energy into nerve impulses at the retina (through rhodopsin).
Protein synthesis and cell differentiation for epithelial tissues (skin and mucous membranes). Reproduction and growth (sperm development, normal fetal development, bone growth).
Beta-carotene acts as an antioxidant.
Deficiency: Impaired immunity, night blindness, xerophthalmia (blindness), keratinization (rough, dry skin).
Toxicity: Bone defects, birth defects, liver abnormalities, visual disturbances, nausea/vomiting, vertigo, and head pressure.
Recommendations (RAE): 900 g RAE/day (men), 700 g RAE/day (women).
Food sources: beef liver, sweet potatoes, carrots.

Other names: Calciferol, 1,25-dihydroxy vitamin D (calcitriol).
Animal versions: vitamin D3 (cholecalciferol).
Plant versions: vitamin D2 (ergocalciferol).
Precursor: cholesterol.
Formation: Produced in the skin when exposed to sunlight. Also obtained through diet.
Roles in the body: maintains blood calcium and phosphorus levels by enhancing their reabsorption from the digestive tract, mobilization from the bones, and stimulating their retention by the kidneys.
Deficiency factors: Breastfeeding without supplements, dark skin, lack of sunlight, and the use of non-fortified milk.
Deficiency symptoms (children-Rickets): Bowed legs, bone deformities, delayed closing of fontanels.
Deficiency symptoms (adults-Osteomalacia): Soft, flexible, brittle and deformed bones; progressive weakness; pain in the pelvis, lower back, and legs.
Toxicity: Hypervitaminosis D, elevated blood calcium, calcification of soft tissues (blood vessels, kidneys, heart, lungs, tissues around joints).
Adequate Intake (AI): 19-50 years: 5 g/day, 51-70 years: 10 g/day, >70years: 15 g/day.
Sources: sunlight, fortified milk, margarine, butter, cereals, chocolate mixes, beef, egg yolks, liver, fatty fish (salmon, sardines).

Four tocopherol compounds; only alpha-tocopherol has Vitamin E activity.
Chief function: antioxidant.
Antioxidant roles: stops free radical chain reactions, protects the oxidation of LDLs, and protects polyunsaturated fatty acids and Vitamin A.
Deficiency: rare, erythrocyte hemolysis (premature infants).
Symptoms: loss of muscle coordination/reflexes, impaired vision/speech, nerve damage.
Toxicity: Rare, least toxic fat-soluble vitamin. Upper level for adults is 1000 mg/day. May enhance blood clotting medication effects.
Recommended Daily Allowance (RDA): Adults: 15 mg/day.
Significant Sources: polyunsaturated plant oils (margarine, salad dressings, shortenings), leafy green vegetables, wheat germ, whole grains, liver, egg yolks, nuts, seeds.

Chief function: synthesis of blood-clotting proteins and bone proteins that regulate blood calcium.
Deficiency: rare, hemorrhaging symptoms. Secondary deficiencies may occur in individuals using antibiotics.
Newborn infants receive a single dose at birth for a sterile intestinal tract.
Toxicity: uncommon, no known toxicities.
Recommendations: AI men: 120 g/day, AI Women: 90 g/day.
Sources: Bacterial synthesis in the digestive tract, liver, leafy green vegetables, cabbage-type vegetables, and milk.