How Vitamins and Minerals Work: Functions, Deficiencies, and Daily Requirements
A comprehensive, evidence-based guide to vitamins and minerals — what they are, their biological functions, recommended daily intakes, deficiency diseases, and the evidence on supplementation.
What Are Vitamins and Minerals?
Vitamins and minerals are micronutrients — essential nutrients required by the body in small amounts for normal growth, metabolism, and physiological function. Unlike macronutrients (carbohydrates, proteins, fats), micronutrients provide no calories but are indispensable cofactors, coenzymes, structural components, and regulators of virtually every biochemical process in the body.
There are 13 essential vitamins and approximately 16 essential minerals. "Essential" means the body cannot synthesize them in adequate quantities (with a few exceptions) and must obtain them from food. This article is for educational purposes. Consult a healthcare provider or registered dietitian before beginning any supplementation regimen.
Vitamins: Fat-Soluble vs. Water-Soluble
Vitamins are classified by how they are absorbed and stored:
Fat-Soluble Vitamins (A, D, E, K)
Absorbed with dietary fat; stored in fatty tissue and the liver. Because they accumulate, deficiency develops slowly but toxicity from excess supplementation is possible.
| Vitamin | Key Functions | Deficiency Disease | Food Sources |
|---|---|---|---|
| Vitamin A (retinol) | Vision (rhodopsin synthesis), immune function, cell differentiation, gene regulation | Night blindness; xerophthalmia; increased infection susceptibility | Liver, dairy, eggs; beta-carotene in orange/yellow vegetables |
| Vitamin D (calciferol) | Calcium absorption regulation; bone mineralization; immune modulation; cell growth regulation | Rickets (children); osteomalacia (adults); increased fracture risk | Sunlight (skin synthesis); fatty fish; fortified dairy; egg yolk |
| Vitamin E (tocopherols) | Antioxidant; protects cell membranes from oxidative damage; immune function | Rare; peripheral neuropathy, hemolytic anemia in deficiency | Nuts, seeds, vegetable oils, green leafy vegetables |
| Vitamin K (phylloquinone, menaquinones) | Coagulation factor synthesis (factors II, VII, IX, X); bone metabolism (osteocalcin carboxylation) | Excessive bleeding; impaired bone metabolism | Green leafy vegetables (K1); fermented foods, some cheeses (K2) |
Water-Soluble Vitamins (B vitamins + Vitamin C)
Absorbed directly into the bloodstream; not stored significantly (except B12); excess excreted in urine. Regular dietary intake is needed; deficiency develops faster than with fat-soluble vitamins.
| Vitamin | Key Functions | Deficiency Disease | Sources |
|---|---|---|---|
| B1 (Thiamine) | Carbohydrate metabolism; nerve function | Beriberi (neurological); Wernicke-Korsakoff syndrome (in alcoholism) | Whole grains, legumes, pork |
| B2 (Riboflavin) | Electron carrier (FAD/FMN); energy metabolism; antioxidant recycling | Ariboflavinosis: cracked lips, sore throat, skin inflammation | Dairy, meat, eggs, leafy vegetables |
| B3 (Niacin) | Electron carrier (NAD+/NADH); DNA repair; cell signaling | Pellagra: dermatitis, diarrhea, dementia, death | Meat, poultry, fish, peanuts, whole grains |
| B5 (Pantothenic acid) | Coenzyme A synthesis; fatty acid metabolism | Rare; burning feet syndrome | Widespread in foods |
| B6 (Pyridoxine) | Amino acid metabolism; neurotransmitter synthesis; hemoglobin production | Peripheral neuropathy, microcytic anemia, dermatitis | Poultry, fish, potatoes, bananas |
| B7 (Biotin) | Fatty acid synthesis; gluconeogenesis; amino acid catabolism | Rare; hair loss, rash, neurological symptoms | Eggs, nuts, seeds, liver |
| B9 (Folate/Folic acid) | DNA synthesis and repair; cell division; neural tube development in fetus | Megaloblastic anemia; neural tube defects (spina bifida) in pregnancy | Leafy greens, legumes, fortified grains |
| B12 (Cobalamin) | DNA synthesis; myelin sheath maintenance; red blood cell formation; folate metabolism | Megaloblastic anemia; irreversible neurological damage if prolonged | Animal products only (meat, fish, dairy, eggs); vegans require supplementation |
| Vitamin C (Ascorbic acid) | Collagen synthesis; antioxidant; iron absorption enhancement; immune function | Scurvy: bleeding gums, poor wound healing, fatigue, death | Citrus fruits, bell peppers, kiwi, strawberries, broccoli |
Essential Minerals
Minerals are inorganic elements with structural and regulatory roles. Macrominerals are needed in relatively large amounts (hundreds of mg/day); trace minerals are needed in small amounts (micrograms to a few mg/day) but are no less essential.
Key Macrominerals
- Calcium: Most abundant mineral in the body (~1 kg in adult); bone and tooth structure (99%); nerve conduction; muscle contraction; blood clotting. Deficiency → osteoporosis (long-term). RDA: 1,000–1,200 mg/day. Sources: dairy, fortified plant milks, sardines with bones, leafy greens.
- Phosphorus: Bone structure; energy transfer (ATP); cell membranes (phospholipids); DNA backbone. Deficiency rare (widespread in foods). RDA: 700 mg/day.
- Magnesium: Cofactor for 300+ enzymatic reactions; ATP stabilization; protein synthesis; nerve and muscle function; blood glucose regulation. Deficiency common in Western diets; associated with hypertension, type 2 diabetes. RDA: 320–420 mg/day. Sources: nuts, seeds, legumes, whole grains, dark leafy vegetables.
- Potassium: Fluid balance; nerve conduction; muscle contraction; blood pressure regulation. Low intake is a major contributor to hypertension. Adequate intake: 2,600–3,400 mg/day. Sources: bananas, potatoes, legumes, dairy, leafy greens.
- Sodium: Fluid balance; nerve conduction; muscle contraction. Most Western adults consume far too much (~3,400 mg/day vs. recommended <2,300 mg) — a major hypertension risk factor. Sources: table salt, processed foods (dominant source).
Key Trace Minerals
- Iron: Hemoglobin oxygen transport; myoglobin; electron transport chain enzymes. Iron deficiency anemia is the world's most common nutritional deficiency, affecting ~1.6 billion people (WHO). Two forms: heme iron (animal sources, well absorbed) and non-heme iron (plant sources, less absorbed; enhanced by vitamin C). RDA: 8 mg (men), 18 mg (women of reproductive age).
- Zinc: Cofactor for 100+ enzymes; immune function; wound healing; DNA synthesis; taste and smell. Deficiency causes impaired immunity, growth retardation, skin lesions. RDA: 8–11 mg/day. Sources: meat, shellfish (especially oysters), legumes, seeds.
- Iodine: Thyroid hormone synthesis (T3, T4); metabolic regulation; fetal brain development. Deficiency → goiter, hypothyroidism; fetal deficiency → cretinism (irreversible intellectual disability). Iodized salt programs have nearly eliminated endemic iodine deficiency in many countries but it remains a problem in others. RDA: 150 μg/day.
- Selenium: Antioxidant enzyme component (glutathione peroxidase); thyroid hormone metabolism; immune function. Deficiency → Keshan disease (cardiomyopathy). Sources: Brazil nuts (highest known food source), seafood, meat.
The Evidence on Supplementation
While supplements are essential for specific deficiencies and certain populations, evidence for routine supplementation in non-deficient individuals is limited or negative:
- Vitamin D: Widespread insufficiency in populations with limited sun exposure; supplementation beneficial for deficient individuals and bone health; evidence for other claimed benefits (cancer prevention, cardiovascular) is mixed in clinical trials.
- Vitamin B12: Supplementation essential for vegans/vegetarians; older adults with reduced absorption; those on long-term metformin (which reduces B12 absorption).
- Folate: Critical periconceptionally — women planning pregnancy should supplement 400–800 μg/day to prevent neural tube defects.
- Multivitamins: Large-scale trials (COSMOS, Physicians' Health Study II) show minimal mortality or disease prevention benefit in well-nourished adults; primary benefit is reducing deficiency in those with poor diets.
- Antioxidant supplements at high doses (beta-carotene, vitamin E, vitamin A): May increase rather than decrease mortality risk in some populations — unlike the antioxidants in whole foods, isolated high-dose antioxidant supplements can have pro-oxidant effects in certain contexts.