Fat-Soluble Vitamins

Overview of Vitamins and Classification by Solubility

Vitamins are organic compounds essential for normal physiological function, growth, and maintenance. They are classified based on their solubility into fat-soluble (A, D, E, K) and water-soluble (B-complex, C) vitamins.

• Fat-soluble vitamins are absorbed with dietary fat, stored in the liver and adipose tissue, and can accumulate to toxic levels.

• Water-soluble vitamins are absorbed directly into the bloodstream, are not stored in large amounts, and excess is excreted in urine.

Antioxidants and Free Radicals

Antioxidants are substances that neutralize free radicals, preventing cellular damage. Vitamins A (as beta-carotene), C, and E function as antioxidants.

• Free radicals are unstable molecules that can damage cells, contributing to aging and diseases.

• Antioxidants from foods are generally more beneficial than supplements due to synergistic effects and lower risk of toxicity.

Bioavailability, Absorption, Transport, Storage, and Toxicity

• Bioavailability refers to the proportion of a nutrient that is absorbed and utilized.

• Fat-soluble vitamins require bile and dietary fat for absorption, are transported via chylomicrons, and stored in the liver/adipose tissue.

• Water-soluble vitamins are absorbed directly into the blood and are not stored extensively.

• Fat-soluble vitamins are more likely to cause toxicity due to storage capacity.

Factors Affecting Vitamin Content of Foods

• Heat, light, and oxidation can degrade vitamins, especially water-soluble ones and vitamin A.

• Proper storage and minimal processing help preserve vitamin content.

Vitamin A

• Types: Retinoids (animal sources), carotenoids (plant sources).

• Functions: Vision, immune function, reproduction, cellular communication.

• Food sources: Liver, dairy, carrots, sweet potatoes, leafy greens.

• Deficiency: Night blindness, xerophthalmia, increased infection risk. Most common in developing countries, especially among children and pregnant women.

• Toxicity: Hypervitaminosis A, teratogenic effects.

Vitamin D

• Types: D2 (ergocalciferol, plant), D3 (cholecalciferol, animal/synthesized in skin).

• Synthesis: UV light converts 7-dehydrocholesterol in skin to vitamin D3.

• Functions: Calcium and phosphorus homeostasis, bone health.

• Food sources: Fatty fish, fortified milk, egg yolks.

• Deficiency: Rickets (children), osteomalacia (adults). Risk factors: limited sun exposure, dark skin, elderly.

• Toxicity: Hypercalcemia, calcification of soft tissues.

Vitamin D and Calcium Regulation:

• Vitamin D increases intestinal absorption of calcium and phosphorus.

• Maintains blood calcium via effects on bone, kidneys, and intestine.

Vitamin E

• Types: Tocopherols and tocotrienols (alpha-tocopherol is most active).

• Functions: Antioxidant, protects cell membranes.

• Food sources: Vegetable oils, nuts, seeds, green leafy vegetables.

• Deficiency: Rare, but can cause hemolytic anemia, neuromuscular problems (at-risk: premature infants, fat malabsorption disorders).

• Toxicity: Rare, but may interfere with vitamin K and increase bleeding risk.

Vitamin K

• Types: Phylloquinone (K1, plants), menaquinone (K2, bacteria/animal foods).

• Functions: Blood clotting, bone metabolism.

• Food sources: Green leafy vegetables, broccoli, Brussels sprouts.

• Deficiency: Impaired blood clotting, risk in newborns and those with fat malabsorption.

• Toxicity: Rare, but can interfere with anticoagulant medications.

Dietary Supplements

• Supplements are not essential for everyone; a balanced diet is preferred.

• May benefit those with increased needs or restricted diets (e.g., pregnancy, elderly, vegans).

• Regulation in the U.S. is less strict than for drugs; safety and efficacy are not always guaranteed.

Water-Soluble Vitamins

Properties and Functions

• Include B-complex vitamins and vitamin C.

• Generally act as coenzymes in energy metabolism and other cellular processes.

• Not stored extensively; regular intake is necessary.

• More susceptible to destruction by heat, light, and oxidation.

• Deficiency risk is higher in populations with poor dietary intake, malabsorption, or increased needs.

Thiamin (Vitamin B1)

• Functions: Coenzyme in carbohydrate metabolism (as TPP).

• Food sources: Whole grains, pork, legumes, nuts.

• Deficiency: Beriberi (wet: cardiovascular, dry: neurological), Wernicke-Korsakoff syndrome (alcoholics).

Riboflavin (Vitamin B2)

• Functions: Coenzyme in energy metabolism (FAD, FMN).

• Food sources: Dairy, eggs, green vegetables, enriched grains.

• Deficiency: Ariboflavinosis (sore throat, cracks at mouth corners).

• Destruction: Easily destroyed by light (milk in opaque containers).

Niacin (Vitamin B3)

• Functions: Coenzyme in energy metabolism (NAD, NADP).

• Food sources: Meat, fish, poultry, whole grains.

• Deficiency: Pellagra (dermatitis, diarrhea, dementia, death).

• Toxicity: Niacin flush, liver damage (pharmacological doses for cholesterol).

Pantothenic Acid (Vitamin B5)

• Functions: Component of coenzyme A, essential for fatty acid metabolism.

• Food sources: Widespread in foods (meats, whole grains, vegetables).

Biotin (Vitamin B7)

• Functions: Coenzyme in carboxylation reactions (fatty acid synthesis).

• Food sources: Eggs, nuts, legumes, whole grains.

• Deficiency: Rare; can be induced by raw egg whites (avidin binds biotin, reducing absorption).

• Toxicity: None reported.

Vitamin B6 (Pyridoxine)

• Functions: Amino acid metabolism, neurotransmitter synthesis.

• Food sources: Meat, fish, potatoes, bananas.

• Deficiency: Dermatitis, anemia, neurological symptoms.

• Toxicity: Nerve damage at high supplemental doses.

Folate (Vitamin B9) and Folic Acid

• Functions: DNA synthesis, cell division, amino acid metabolism, homocysteine metabolism.

• Food sources: Leafy greens, legumes, fortified grains.

• Deficiency: Neural tube defects, macrocytic anemia.

• Toxicity: Can mask B12 deficiency.

• Folate vs. Folic Acid: Folate is natural form; folic acid is synthetic, more bioavailable.

Vitamin B12 (Cobalamin)

• Functions: Nerve function, red blood cell formation, DNA synthesis.

• Food sources: Animal products only (meat, dairy, eggs).

• Deficiency: Macrocytic anemia, neurological symptoms. At risk: vegans, elderly (reduced intrinsic factor).

• Intrinsic factor: Protein required for B12 absorption in the small intestine.

Vitamin C (Ascorbic Acid)

• Functions: Antioxidant, collagen synthesis, enhances iron absorption.

• Food sources: Citrus fruits, strawberries, peppers, broccoli.

• Deficiency: Scurvy (bleeding gums, poor wound healing).

• Toxicity: GI upset, kidney stones at high doses.

• Supplements: Limited evidence for preventing common cold.

Diet, Lifestyle, and Cancer Risk

• High intake of fruits, vegetables, and whole grains is associated with reduced cancer risk.

• Limit processed meats, alcohol, and maintain healthy weight.

Major Minerals

Major vs. Trace Minerals

• Major minerals are required in amounts >100 mg/day (e.g., sodium, potassium, calcium, phosphorus, magnesium, chloride, sulfur).

• Trace minerals are needed in smaller amounts (<100 mg/day).

• Solubility, stability, and toxicity can be affected by heat, light, and oxidation.

Bioavailability of Minerals

• Factors increasing bioavailability: vitamin C (for iron), stomach acid, certain food forms.

• Factors reducing bioavailability: phytates, oxalates, polyphenols, high fiber, competition among minerals.

Absorption, Transport, and Storage

• Absorbed in the intestine, transported in blood (sometimes bound to proteins), stored in various tissues.

Sodium

• Functions: Fluid balance, nerve transmission, muscle contraction.

• Food sources: Processed foods, table salt.

• RDA/UL: RDA ~1,500 mg; UL 2,300 mg/day.

• Toxicity: Hypertension, cardiovascular risk.

• DASH Diet: Emphasizes potassium, calcium, magnesium; reduces sodium intake.

Potassium

• Functions: Fluid balance, nerve and muscle function.

• Food sources: Fruits, vegetables, dairy, legumes.

• Deficiency: Muscle weakness, arrhythmias (at-risk: diuretic users, eating disorders).

Calcium

• Functions: Bone and teeth structure, muscle contraction, nerve signaling.

• Food sources: Dairy, fortified foods, leafy greens.

• Bioavailability: Enhanced by vitamin D; reduced by oxalates, phytates.

• Blood calcium regulation: Maintained by parathyroid hormone, vitamin D, and calcitonin.

• Deficiency: Osteoporosis risk (elderly, postmenopausal women).

• Supplement tips: Divide doses, take with meals, avoid excess.

Phosphorus

• Functions: Bone structure, energy metabolism (ATP), cell membranes.

• Food sources: Meat, dairy, nuts, legumes.

• Deficiency: Rare, but can contribute to bone loss.

Magnesium

• Functions: Enzyme cofactor, bone health, muscle function.

• Food sources: Nuts, whole grains, leafy greens.

• Deficiency: Uncommon; possible with alcoholism, GI disorders.

Sulfate/Sulfur

• Functions: Component of amino acids, vitamins, and other compounds.

• Food sources: Protein-rich foods.

Chloride

• Functions: Fluid balance, stomach acid (HCl) production.

• Food sources: Table salt, processed foods.

Bone Health and Osteoporosis

• Minerals (calcium, phosphorus, magnesium) are critical for bone structure.

• Osteoporosis risk factors: age, gender, genetics, low calcium/vitamin D, inactivity, smoking.

• Treatment: Diet, exercise, medications (bisphosphonates, hormone therapy).

Trace Minerals

Characteristics and Functions

• Needed in small amounts but essential for health (iron, zinc, copper, selenium, fluoride, chromium, iodine, manganese, molybdenum).

• Bioavailability affected by dietary factors and stomach acidity.

Soil Content and Food Processing

• Mineral content of foods depends on soil composition and processing methods.

Iron

• Types: Heme (animal foods, better absorbed), nonheme (plant foods).

• Functions: Oxygen transport (hemoglobin, myoglobin), energy metabolism.

• Food sources: Red meat, beans, fortified cereals.

• Absorption: Enhanced by vitamin C, inhibited by phytates, calcium.

• Regulation: Hepcidin (hormone) decreases absorption; ferritin stores iron.

• Deficiency: Iron-deficiency anemia (at-risk: women, children, vegetarians).

• Toxicity: Hemochromatosis (genetic iron overload).

Copper

• Functions: Iron metabolism, antioxidant enzymes.

• Food sources: Shellfish, nuts, seeds, whole grains.

• Deficiency: Anemia, immune dysfunction.

• Genetic diseases: Wilson's disease (copper accumulation), Menkes disease (copper deficiency).

Zinc

• Functions: Enzyme function, immune health, wound healing.

• Food sources: Meat, seafood, whole grains.

• Deficiency: Growth retardation, impaired immunity.

• Supplements: May reduce duration of common cold, but evidence is mixed.

Selenium

• Functions: Antioxidant (glutathione peroxidase), thyroid hormone metabolism.

• Food sources: Brazil nuts, seafood, meats.

• Deficiency: Keshan disease (heart), possible increased cancer risk (prostate cancer).

Fluoride

• Functions: Tooth enamel strength, bone health.

• Food sources: Fluoridated water, tea, seafood.

• Toxicity: Fluorosis (mottled teeth).

• No strong evidence linking fluoride to cancer or ADHD.

Chromium

• Functions: Enhances insulin action, glucose metabolism.

• Food sources: Whole grains, meats, broccoli.

• Adequate intake may benefit those with impaired glucose tolerance.

Iodine

• Functions: Thyroid hormone synthesis.

• Food sources: Iodized salt, seafood, dairy.

• Deficiency: Goiter, hypothyroidism, cretinism.

• Goitrogens: Substances in some foods (e.g., cabbage, soy) that inhibit iodine utilization.

Molybdenum and Manganese

• Both are trace minerals required for enzyme function.

• Found in a variety of plant foods.

Nutrient-Deficiency Anemias

• Anemia: Reduced oxygen-carrying capacity of blood.

• Macrocytic anemia: Large, immature red blood cells (folate or B12 deficiency).

• Microcytic anemia: Small, pale red blood cells (iron deficiency).

• Iron, folate, and B12 deficiencies are common causes of anemia.