Vitamins: Characteristics, Functions, and Health Implications

General Characteristics of Vitamins

Vitamins are organic compounds essential for normal physiological function, growth, and maintenance. They are required in small amounts and must be obtained from the diet, as the body either cannot synthesize them or cannot synthesize them in sufficient quantities.

• Number and Names: There are 13 essential vitamins, divided into fat-soluble (A, D, E, K) and water-soluble (B-complex and C) groups.

• Solubility: Fat-soluble vitamins are absorbed with dietary fat and stored in body tissues; water-soluble vitamins are not stored in significant amounts and excess is excreted in urine.

• Functions: Each vitamin has specific roles, such as acting as coenzymes, antioxidants, or regulators of gene expression.

Bioavailability

Bioavailability refers to the proportion of a nutrient that is absorbed and utilized by the body. Factors affecting bioavailability include food matrix, preparation, nutrient-nutrient interactions, and individual health status.

Hypervitaminosis

Excessive intake of certain vitamins, especially fat-soluble ones, can lead to hypervitaminosis, causing toxicity symptoms. For example, too much vitamin A can cause liver damage and birth defects.

Fat-Soluble Vitamins

• Absorption: Require dietary fat and bile for absorption; absorbed in the small intestine.

• Transport: Carried in chylomicrons via the lymphatic system.

• Storage: Stored in liver and adipose tissue.

Vitamin A

• Forms: Retinol (active form), retinal, retinoic acid, and provitamin A carotenoids (e.g., beta-carotene).

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

• Food Sources: Liver, dairy, fish, orange/yellow vegetables (carrots, sweet potatoes).

• Deficiency: Night blindness, xerophthalmia, increased infection risk.

• Toxicity: Hypervitaminosis A, birth defects, liver abnormalities.

• Beta-carotene: A provitamin A carotenoid; excess can cause carotenodermia (yellowing of skin).

Vitamin D

• Functions: Calcium and phosphorus homeostasis, bone health, immune modulation.

• Food Sources: Fatty fish, fortified dairy, egg yolks; also synthesized in skin via sunlight.

• Deficiency: Rickets (children), osteomalacia (adults).

• Toxicity: Hypercalcemia, kidney stones.

• Metabolism: Inactive form (cholecalciferol) converted to active form (calcitriol) in liver and kidneys.

Vitamin E

• Functions: Antioxidant, protects cell membranes from oxidative damage.

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

• Deficiency: Rare; can cause nerve and muscle damage.

• Toxicity: May interfere with vitamin K and blood clotting.

Vitamin K

• Functions: Blood clotting (synthesis of clotting factors), bone metabolism.

• Food Sources: Green leafy vegetables, broccoli, Brussels sprouts; also synthesized by gut bacteria.

• Deficiency: Impaired blood clotting, hemorrhage.

• Toxicity: Rare; can interfere with anticoagulant medications (e.g., Coumadin).

• Infant Needs: Newborns require vitamin K injection to prevent bleeding disorders.

Antioxidants and Phytochemicals

• Antioxidants: Vitamins (A, C, E) and minerals (selenium, zinc) that neutralize free radicals, reducing oxidative stress.

• Phytochemicals: Plant compounds with health benefits, such as beta-carotene, flavonoids, lutein, and zeaxanthin.

• Carotenoids: Pigments in plants; some are provitamin A (e.g., beta-carotene).

Vitamin Fortification and Preservation

• Fortification: Addition of vitamins to foods to prevent deficiencies (e.g., vitamin D in milk).

• Enrichment: A form of fortification; restoring nutrients lost during processing (e.g., B vitamins in flour).

• Preservation: Store vitamins away from heat, light, and air; minimize cooking time and water use.

Supplements

• Approval: Not regulated as strictly as drugs; look for USP symbol for quality.

• Who Needs Them: Pregnant women, elderly, those with restricted diets.

• Who Doesn't: Most healthy adults with balanced diets.

Water-Soluble Vitamins: B-Complex and Vitamin C

General Characteristics

• Absorption: Directly into bloodstream; not stored extensively.

• Excretion: Excess excreted in urine; toxicity is rare.

B Vitamins

• Primary Function: Act as coenzymes in energy metabolism.

• Energy Production: Thiamin, riboflavin, niacin, pantothenic acid, and biotin are involved in ATP production.

• Riboflavin: Forms FMN and FAD, essential for energy metabolism.

• Niacin: Forms NAD and NADP, key in redox reactions.

• Pantothenic Acid: Part of coenzyme A (acetyl CoA), central in metabolism.

• Folate: RDA is higher for pregnant women; folic acid is the synthetic form.

• Vitamin B12: Requires intrinsic factor for absorption; deficiency leads to pernicious anemia.

• Biotin: Binds to avidin in raw egg whites, reducing absorption.

Vitamin C

• Functions: Collagen synthesis, antioxidant, enhances iron absorption, immune support.

• Food Sources: Citrus fruits, strawberries, bell peppers, broccoli.

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

• Toxicity: Gastrointestinal upset, kidney stones (in susceptible individuals).

Deficiency Diseases

• Beriberi: Thiamin deficiency; affects nervous and cardiovascular systems.

• Wernicke-Korsakoff Syndrome: Severe thiamin deficiency, often in alcoholics.

• Pellagra: Niacin deficiency; characterized by the "4 Ds": dermatitis, diarrhea, dementia, death.

• Ariboflavinosis: Riboflavin deficiency; causes sore throat, cracks at mouth corners.

• Anemias: Various types due to deficiencies in B12, folate, or iron.

Major Minerals: Functions, Sources, and Regulation

General Characteristics

• Major vs. Trace Minerals: Major minerals are required in amounts >100 mg/day (e.g., calcium, sodium, potassium); trace minerals are needed in smaller amounts.

• Bioavailability: Influenced by binders (oxalates, phytates, polyphenols), competition, and vitamin interactions.

Calcium (Ca)

• Most abundant mineral in the body.

• Functions: Bone and teeth structure, muscle contraction, nerve transmission, blood clotting.

• Homeostasis: Regulated by parathyroid hormone (PTH), calcitonin, and vitamin D (calcitriol).

• Bioavailability: Enhanced by vitamin D; inhibited by oxalates and phytates.

• Supplements: Calcium carbonate and citrate; absorption best at doses ≤500 mg at a time.

• Deficiency: Osteoporosis, muscle spasms.

• Toxicity: Hypercalcemia, kidney stones.

Sodium (Na)

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

• Sources: Table salt (NaCl), processed foods.

• AI: 1,500 mg/day for adults; upper limit 2,300 mg/day.

• Deficiency: Rare; can cause hyponatremia.

• Toxicity: Hypertension, increased cardiovascular risk.

• Balance: Maintained by kidneys.

Potassium (K)

• Major intracellular cation.

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

• AI: 4,700 mg/day; most people do not meet this requirement.

• Deficiency: Hypokalemia (muscle weakness, arrhythmias).

• Toxicity: Hyperkalemia (can be life-threatening).

Chloride (Cl)

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

• Sources: Table salt, processed foods.

Magnesium (Mg)

• Functions: Cofactor for 300+ enzymes, bone health, blood pressure regulation.

• Sources: Nuts, whole grains, leafy greens.

• Deficiency: Muscle cramps, arrhythmias.

Sulfate (SO42-)

• Functions: Component of amino acids and vitamins; helps prevent food discoloration.

• Sensitivity: Sulfites in wine can cause reactions in sensitive individuals.

Bone Health and Osteoporosis

• Bone Composition: Minerals (calcium, phosphorus, magnesium) and vitamins (D, K).

• Osteoporosis: Reduced bone mass and increased fracture risk.

• Regulation: Parathyroid hormone, calcitonin, and vitamin D maintain calcium balance.

Dietary Approaches to Stop Hypertension (DASH) and Mediterranean Diet

• DASH Diet: Emphasizes fruits, vegetables, whole grains, low-fat dairy, and reduced sodium to lower blood pressure.

• Mediterranean Diet: High in fruits, vegetables, whole grains, olive oil, and fish; associated with cardiovascular benefits.

Binders

• Definition: Compounds that reduce mineral absorption by forming insoluble complexes.

• Examples: Oxalates (spinach), phytates (whole grains), polyphenols (tea, coffee).

Trace Minerals: Functions, Sources, and Deficiencies

General Characteristics

• Trace minerals are required in amounts less than 100 mg/day and are essential for various physiological functions.

• Initial Source: Soil; content in food depends on soil composition.

• Metalloenzymes: Many trace minerals are components of enzymes (metalloenzymes).

Iron (Fe)

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

• Forms: Heme (animal sources, better absorbed), non-heme (plant sources).

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

• Deficiency: Iron-deficiency anemia (fatigue, weakness).

• Toxicity: Hemochromatosis (iron overload), iron poisoning.

• Storage: Ferritin, hemosiderin.

• Transport: Transferrin.

• Regulation: Hepcidin controls absorption.

• Requirements: Higher for women of childbearing age; lower after menopause.

Copper (Cu)

• Functions: Collagen and elastin synthesis, antioxidant defense (superoxide dismutase).

• Deficiency: Anemia, connective tissue disorders.

• Toxicity: Wilson's disease (copper accumulation).

Zinc (Zn)

• Functions: Protein synthesis, immune function, wound healing, taste perception.

• Sources: Meat, seafood, whole grains.

• Deficiency: Impaired growth, immune dysfunction.

• Vegetarians: At higher risk due to lower bioavailability from plant sources.

Selenium (Se)

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

• Deficiency: Keshan disease (heart disorder).

• Toxicity: Selenosis (hair loss, nerve damage).

Fluoride (F)

• Functions: Strengthens tooth enamel (fluorapatite), prevents dental caries.

• Sources: Fluoridated water, tea, fish.

• Toxicity: Fluorosis (mottled teeth).

Chromium (Cr)

• Functions: Enhances insulin action, regulates blood glucose.

Manganese (Mn)

• Functions: Cofactor for metalloenzymes, bone and cartilage formation.

Iodine (I)

• Functions: Synthesis of thyroid hormones (T3, T4).

• Sources: Iodized salt, seafood.

• Deficiency: Goiter (enlarged thyroid), cretinism (developmental delays in infants).

• Goiter Types: Primary (iodine deficiency), secondary (thyroid dysfunction).

Nutritional Anemias

• Iron-deficiency anemia: Microcytic, hypochromic anemia due to low iron.

• Pernicious anemia: Due to vitamin B12 deficiency, often from lack of intrinsic factor.

• Folate-deficiency anemia: Megaloblastic anemia, common in pregnancy.

Table: Overview of Fat-Soluble Vitamins (Table 9.1)

Additional info:

• Vitamin and mineral interactions can affect absorption (e.g., vitamin C enhances iron absorption; calcium can inhibit iron absorption).

• Supplements should not replace a balanced diet and may be necessary only in specific populations.

• Metalloenzymes are enzymes that require a metal ion (such as zinc or copper) for activity.