Fat-Soluble Vitamins Overview

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

• 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.

Solubility and Storage of Vitamins

• 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

• 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.

Vitamin D

• 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).

Vitamin E

• 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.

Vitamin K

• 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.

This quiz explores the essential fat-soluble vitamins A, D, E, and K, outlining their importance, absorption, and storage in the body. Learn about their sources, bioavailability, and the differences between fat-soluble and water-soluble vitamins. Test your knowledge on how these nutrients impact health.