Vitamins are organic substances that are important in the regulation of the body's processes. Vitamins may be
Fat soluble (vitamins A, D, E, and K)
Water soluble (B vitamins and vitamin C)
The B vitamins include biotin, folate, niacin, pantothenic acid, riboflavin (B2), thiamine (B1), B6 (eg, pyridoxine), and B12 (cobalamins).
For dietary requirements, sources, functions, effects of deficiencies and toxicities, blood levels, and usual therapeutic dosages for vitamins, see tables and .
Dietary requirements for vitamins (and other nutrients) are expressed as daily recommended intake (DRI). There are 3 types of DRI:
Recommended dietary allowance (RDA): RDAs are average daily dietary intake levels set to meet the needs of 97 to 98% of healthy people.
Adequate intake (AI): When data to calculate an RDA are insufficient, AIs are based on observed or experimentally determined estimates of nutrient intake by healthy people.
Tolerable upper intake level (UL): ULs are the largest amount of a nutrient that most adults can ingest daily without risk of adverse health effects.
In countries with low rates of food insecurity, vitamin deficiencies result mainly from the following:
Poverty
Food faddism
Medications, drugs, and foods (see Nutrient-Drug Interactions and table )
Prolonged and inadequately supplemented parenteral nutrition
Mild vitamin deficiency is common among older adults who are frail and institutionalized and who have protein-energy undernutrition.
In countries with high rates of food insecurity, vitamin deficiencies can result from lack of access to nutrients. Deficiencies of water-soluble vitamins (except vitamin B12) may develop after weeks to months of undernutrition. Deficiencies of fat-soluble vitamins and of vitamin B12 take > 1 year to develop, because the body stores them in relatively large amounts. Intakes of vitamins sufficient to prevent classic diseases vitamin deficiencies (such as scurvy or beriberi) may not be adequate for optimum health. Vitamin D supplementation did not benefit patients with COVID-19 infections. This area remains one of controversy and active research.
Vitamin dependency results from a genetic defect involving metabolism of a vitamin. In some cases, vitamin doses as high as 1000 times the DRI improve function of the altered metabolic pathway.
Vitamin toxicity (hypervitaminosis) usually results from taking megadoses of vitamin A, D, C, B6, or niacin.
Because many people eat irregularly, foods alone may provide suboptimal amounts of some vitamins. In these cases, the risk of certain cancers or other disorders may be increased. However, the latest 2022 report from the U.S. Preventive Services Task Force finds that, after a thorough review of scientific research, there is insufficient evidence that routine daily multivitamin supplements or individual vitamin and mineral supplementation can reduce incidence of cancer or prevent cardiovascular disease (1, 2) in community-dwelling, nonpregnant adults. No association has been found between daily multivitamin use over 20 years and longevity in generally healthy adults in the United States (3). Multiple vitamin supplementation may improve performance on some mental status tests, but is unlikely to have clinically meaningful benefits or to slow the progression of dementia (4).
Recommended Daily Intakes for Vitamins
Age | Folate (mcg) | Niacin (mg NE*) | Riboflavin (mg) | Thiamine (mg) | Vitamin A (mcg) | Vitamin B6 (mg) | Vitamin B12 (mcg) | Vitamin C (mg) | Vitamin D (IU)† | Vitamin E (mg) | Vitamin K (mcg) |
|---|---|---|---|---|---|---|---|---|---|---|---|
Infants | |||||||||||
0–6 months | 65 | 2 | 0.3 | 0.2 | 400 | 0.1 | 0.4 | 40 | 400 | 4 | 2.0 |
7–12 months | 80 | 4 | 0.4 | 0.3 | 500 | 0.3 | 0.5 | 50 | 400 | 5 | 2.5 |
Children | |||||||||||
1–3 years | 150 | 6 | 0.5 | 0.5 | 300 | 0.5 | 0.9 | 15 | 600 | 6 | 30 |
4–8 years | 200 | 8 | 0.6 | 0.6 | 400 | 0.6 | 1.2 | 25 | 600 | 7 | 55 |
Males | |||||||||||
9–13 years | 300 | 12 | 0.9 | 0.9 | 600 | 1.0 | 1.8 | 45 | 600 | 11 | 60 |
14–18 years | 400 | 16 | 1.3 | 1.2 | 900 | 1.3 | 2.4 | 75 | 600 | 15 | 75 |
19–70 years | 400 | 16 | 1.3 | 1.2 | 900 | 1.3 | 2.4 | 90 | 600 | 15 | 120 |
> 70 years | 400 | 16 | 1.3 | 1.2 | 900 | 1.7 | 2.4 | 90 | 800‡ | 15 | 120 |
Females | |||||||||||
9–13 years | 300 | 12 | 0.9 | 0.9 | 600 | 1.0 | 1.8 | 45 | 600 | 11 | 60 |
14–18 years | 400 | 14 | 1.0 | 1.0 | 700 | 1.2 | 2.4 | 65 | 600 | 15 | 75 |
19–70 years | 400 | 14 | 1.1 | 1.1 | 700 | 1.3 | 2.4 | 75 | 600 | 15 | 90 |
> 70 years | 400 | 14 | 1.1 | 1.1 | 700 | 1.5 | 2.4 | 75 | 800‡ | 15 | 90 |
Pregnant women | |||||||||||
19–50 years | 600 | 18 | 1.4 | 1.4 | 770 | 1.9 | 2.6 | 85 | 600 | 15 | 90 |
Breastfeeding women | |||||||||||
19–50 years | 500 | 17 | 1.6 | 1.4 | 1300 | 2.0 | 2.8 | 120 | 600 | 19 | 90 |
Upper limit (UL)§ | |||||||||||
1000 | 35 | ND | ND | 3000 | 100 | ND | 2000 | 4000 | 1000 | ND | |
NOTE: Recommended dietary allowances (RDAs) are shown in regular type. RDAs are set to meet the needs of 97 to 98% of healthy people. Adequate intakes (AIs) are shown in bold type. When data to calculate the RDA for a nutrient are insufficient, AIs are based on observed or experimentally determined estimates of nutrient intake by healthy people. | |||||||||||
* 1 niacin equivalent (NE) equals 1 mg niacin or 60 mg dietary tryptophan. | |||||||||||
† 200 IU of vitamin D equals 5 mcg cholecalciferol. | |||||||||||
‡ 800 IU of vitamin D is recommended for people ≥ 70 years. | |||||||||||
§ UL (tolerable upper intake level) is the largest amount of a nutrient that most adults can ingest daily without risk of adverse effects. The more the UL is exceeded, the greater the risk of adverse effects. | |||||||||||
IU = international units; ND = not determinable because of lack of data (sources of intake should be limited to foods); RAE = retinol activity equivalents (1 mcg RAE of preformed vitamin A = 3.33 units). | |||||||||||
Data from National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Energy. Washington (DC): National Academies Press (US); 2023 https://doi.org/10.17226/26818 | |||||||||||
Sources, Functions, and Effects of Vitamins
Nutrient | Principal Sources | Functions | Effects of Deficiency and Toxicity |
|---|---|---|---|
Liver, kidneys, meats, eggs, milk, fish, dried yeast, sweet potatoes, seeds, and nuts | Required for the processing (metabolism) of carbohydrates and fatty acids | Deficiency: Extremely rare | |
Folate (folic acid) | Raw green leafy vegetables, fruits, organ meats (eg, liver), enriched cereals and breads | Maturation of red blood cells Synthesis of purines, pyrimidines, and methionine Development of fetal nervous system | Deficiency: Megaloblastic anemia, neural tube birth defects, confusion |
Niacin (nicotinic acid, nicotinamide) | Liver, red meat, fish, poultry, legumes, whole-grain or enriched cereals and breads | Oxidation-reduction reactions Carbohydrate and cell metabolism | Deficiency: Pellagra (dermatitis, glossitis, gastrointestinal and central nervous system dysfunction) Toxicity: Flushing |
Pantothenic acid | Animal products, many fruits and vegetables, fortified grains | Synthesizing coenzyme A for carbohydrate, protein, and fat metabolism | Deficiency and Toxicity: Extremely rare |
Riboflavin (vitamin B2) | Milk, cheese, liver, meat, fish, eggs, and enriched cereals | Required for the metabolism of carbohydrates and proteins and for healthy mucous membranes, such as those lining the mouth | Deficiency: Cheilosis, angular stomatitis, corneal vascularization |
Thiamine (vitamin B1) | Whole grains, meat (especially pork and liver), enriched cereal products, nuts, legumes, potatoes | Carbohydrate, fat, amino acid, glucose, and alcohol metabolism Central and peripheral nerve cell function Myocardial function | Deficiency: Beriberi (peripheral neuropathy, heart failure), Wernicke-Korsakoff syndrome |
Vitamin A (retinol) | As preformed vitamin: Fish liver oils, liver, egg yolks, butter, vitamin A–fortified dairy products As provitamin carotenoids: Dark green and yellow vegetables, carrots, yellow and orange fruits | Formation of rhodopsin (a photoreceptor pigment in the retina) Integrity of epithelia Lysosome stability Glycoprotein synthesis | Deficiency: Night blindness, perifollicular hyperkeratosis, xerophthalmia, keratomalacia, increased morbidity and mortality in young children Toxicity: Headache, peeling of skin, hepatosplenomegaly, bone thickening, intracranial hypertension, papilledema, hypercalcemia |
Vitamin B6 group (pyridoxine, pyridoxal, pyridoxamine) | Organ meats (eg, liver), whole-grain cereals, fish, legumes | Many aspects of nitrogen metabolism (eg, transaminations, porphyrin and heme synthesis, tryptophan conversion to niacin) Nucleic acid biosynthesis Fatty acid, lipid, and amino acid metabolism | Deficiency: Seizures, anemia, neuropathies, seborrheic dermatitis Toxicity: Peripheral neuropathy |
Vitamin B12 (cobalamins) | Meats (especially beef, pork, and organ meats [eg, liver]), poultry, eggs, fortified cereals, milk and milk products, clams, oysters, mackerel, salmon | Maturation of red blood cells, neural function, DNA synthesis, myelin synthesis and repair | Deficiency: Megaloblastic anemia, neurologic deficits (confusion, paresthesias, ataxia) |
Vitamin C (ascorbic acid) | Citrus fruits, tomatoes, potatoes, broccoli, strawberries, sweet peppers | Collagen formation Bone and blood vessel health Carnitine, hormone, and amino acid formation Wound healing | Deficiency: Scurvy (hemorrhages, loose teeth, gingivitis, bone defects) Toxicity: Hyperoxaluria |
Vitamin D (cholecalciferol, ergocalciferol) | Direct ultraviolet B irradiation of the skin (main source), fortified dairy products (main dietary source), fish liver oils, fatty fish, liver | Calcium and phosphate absorption Mineralization and repair of bone Tubular reabsorption of calcium Insulin and thyroid function, improvement of immune function, reduced risk of autoimmune disease | Deficiency: Rickets (sometimes with tetany), osteomalacia Toxicity: Hypercalcemia, anorexia, renal failure, metastatic calcifications |
Vitamin E group (alpha-tocopherol, other tocopherols) | Vegetable oils, nuts | Intracellular antioxidant Scavenger of free radicals in biologic membranes | Deficiency: Red blood cell hemolysis, neurologic deficits Toxicity: Tendency to bleed |
Vitamin K group (phylloquinone, menaquinones) | Green leafy vegetables (especially collards, spinach, and salad greens), soy beans, vegetable oils Bacteria in the gastrointestinal tract after neonatal period | Formation of prothrombin, other coagulation factors, and bone proteins | Deficiency: Bleeding due to deficiency of prothrombin and other factors, osteopenia |
Potential Vitamin-Drug Interactions
Nutrient | Drug |
|---|---|
Antibiotics, antiseizure medications | |
Alcohol, 5-fluorouracil, metformin, methotrexate, oral contraceptives, antiseizure medications (eg, phenobarbital, phenytoin, primidone), triamterene, trimethoprim | |
Alcohol, isoniazid | |
Alcohol, barbiturates, phenothiazines, thiazide diuretics, tricyclic antidepressants | |
Alcohol; oral contraceptives; thiamine antagonists in coffee, tea, raw fish, and red cabbage | |
Cholestyramine, mineral oil | |
Alcohol, antiseizure medications, glucocorticoids, cycloserine, hydralazine, isoniazid, levodopa, oral contraceptives, penicillamine | |
Antacids, metformin, nitrous oxide (repeated exposure) | |
Corticosteroids | |
Antipsychotics, corticosteroids, mineral oil, antiseizure medications, rifampin | |
Mineral oil, warfarin | |
Antibiotics, antiseizure medications, mineral oil, rifampin, warfarin |
References
1. Jia J, Cameron NA, Linder JA. Multivitamins and Supplements-Benign Prevention or Potentially Harmful Distraction?. JAMA. 2022;327(23):2294-2295. doi:10.1001/jama.2022.9167
2. U.S. Preventive Services Task Force, Mangione CM, Barry MJ, et al. Vitamin, mineral, and multivitamin supplementation to prevent cardiovascular disease and cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 327(23):2326-2333, 2022. doi:10.1001/jama.2022.8970
3. Loftfield E, O'Connell CP, Abnet CC, et al. Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts. JAMA Netw Open. 2024;7(6):e2418729. Published 2024 Jun 3. doi:10.1001/jamanetworkopen.2024.18729
4. Rutjes AW, Denton DA, Di Nisio M, et al. Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life. Cochrane Database Syst Rev. 2018;12(12):CD011906. Published 2018 Dec 17. doi:10.1002/14651858.CD011906.pub2
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