For healthy people, supplements may help prevent vitamin and mineral deficiencies when the diet does not provide all necessary nutrients. They can also supply amounts of nutrients larger than the diet can provide. Larger amounts of some nutrients may help to protect against future disease. Many of these nutrients will be briefly discussed here. However, for more information, refer to individual nutrient articles.
People may consume diets that are deficient in one or more nutrients for a variety of reasons. The typical Western diet often supplies less than adequate amounts of several essential vitamins and minerals.1 Recent nutrition surveys in the U.S. have found large numbers of people consume too little calcium, magnesium, iron, zinc, and, possibly, copper and manganese.2 3
Weight-loss, pure vegetarian, macrobiotic, and several other diets can also place some people at risk of deficiencies that vary with the type of diet. Certain groups of people are at especially high risk of dietary deficiencies. Studies have found that elderly people living in their own homes often have dietary deficiencies of vitamin D, vitamin A, vitamin E, calcium, and zinc,4 and occasionally of vitamin B1 and vitamin B2.5,6 Premenopausal women have been found often to consume low amounts of calcium, iron, vitamin A, and vitamin C.
Dietary deficiency of vitamin A is uncommon in healthy people except in older age groups.7 Although vitamin A is important for the function of the immune system, vitamin A supplementation did not help prevent infections in elderly people living in nursing homes, in one study.8 Due to concerns about birth defects9 and bone loss,10 people should not take over 10,000 IU of supplemental vitamin A in the form of retinol without consulting a doctor.
Some of the B-vitamins, including thiamine (vitamin B1), riboflavin (vitamin B2), and niacin (vitamin B3), may be adequately supplied by the typical Western diet, because they are added to white flour products and other foods that have been depleted of those vitamins. Another vitamin, biotin, is produced by intestinal bacteria in amounts that, along with typical dietary biotin intake, provide enough of this vitamin to prevent deficiency in healthy people. Pantothenic acid (vitamin B5), on the other hand, appears to be in short supply in the typical diet. In one study, 49% of a group of male and female adolescents were consuming less-than-adequate amounts of pantothenic acid in their diet.31 No research has investigated whether supplements of these B-vitamins prevent disease.
Vitamin B6 (pyridoxine) deficiency, at least in a mild form, may exist in 10 to 25% of people living in Western societies,32 and may be most common in the elderly.33 34 35 The possible role of vitamin B6 in the prevention of heart disease by helping to regulate blood homocysteine levels is discussed below. No other research on preventive effects of vitamin B6 supplementation has been done.
Folic acid deficiency has been considered somewhat common in the U.S. It affects about 11% of healthy people,36 with a higher prevalence among African-Americans and Mexican-Americans.37 Recently, however, the U.S. Food and Drug Administration (FDA) mandated that some grain products provide supplemental folic acid. This appears to be causing a reduction in the prevalence of folic acid deficiency in the general population.3839 Nonetheless, some authorities believe the recent increases in folic acid content of the food supply are not enough to optimally prevent diseases such as heart disease and birth defects (see discussions below). The requirement for folic acid doubles during pregnancy,40 and insufficient intake of folic acid has been linked to low birth weight and an increased incidence of neural tube defects in newborns. Supplementation with 400 mcg per day of folic acid prior to, and shortly after, conception is effective in preventing neural tube defects.41
Vitamin B12 deficiency is not common among healthy young people,42 except for vegans (vegetarians who also avoid dairy and eggs).43 However, about 12 to 15% of the elderly in the U.S. have been found deficient in this vitamin.44 45 Vitamin B12 deficiency may also occur in people who take acid-blocking drugs or antacids for long periods of time.46 Although vitamin B12 deficiency in the elderly is often due to age-related declines in absorption of vitamin B12 from food, vitamin B12 supplements can be absorbed sufficiently in members of this age group if they do not have pernicious anemia or other significant gastrointestinal disorders.4748 Supplementation with 100 mcg per day of vitamin B12 was adequate to reverse vitamin B12 deficiency in healthy elderly people, according to one recent report. The B-vitamins folic acid, B12, and pyridoxine (vitamin B6) are important for the control of homocysteine levels in the blood.49 Elevated homocysteine levels are associated with several diseases, including heart disease,50 stroke,51 Alzheimer’s disease,52 and osteoporosis,53 and some, though not all, research suggests that homocysteine has a direct role in causing these diseases. Daily supplementation with these B-vitamins, typically at least 400 mcg of folic acid, 10 mg of vitamin B6, and 50 mcg of vitamin B12, lowers elevated homocysteine levels in most people.54 55 56 Some studies have shown that supplementing with one or more of these vitamins helps prevent or reverse hardening of the arteries (atherosclerosis) and may also reduce the risk of bone fractures.57 58
Severe vitamin C deficiency is uncommon in people who consume Western diets, but mild insufficiency is found in 6% of healthy adults59 and larger numbers of college students60 and smokers.61 On the basis of extensive analyses of published vitamin C studies, some authorities have suggested that optimal intake for disease prevention may be at least 90 to 100 mg per day.62 63 However, supplementation with over 200 mg per day of vitamin C by healthy people does not result in higher vitamin C concentrations in the body,64 and may be no more helpful for preventing disease than smaller amounts.
Vitamin D can be obtained from the diet or from sunlight exposure, but these sources can be insufficient, especially in older people and vegans during the winter months.65 In healthy adult Western European populations, 6 to 14% percent have been reported to be vitamin D deficient,66 but good data are not available for the US. Vitamin D insufficiency is associated with bone loss and fractures in older people.67 68 Reduced bone loss from vitamin D supplements has been reported in some,69 70 though not all,71 studies. In one double-blind study, supplementation with 800 IU per day of vitamin D prevented bone loss more effectively than 200 IU per day in postmenopausal women.72 In addition, vitamin D supplementation has been shown to reduce the risk of falls in older people.73 While vitamin D is known to be toxic in very high amounts, up to 2000 IU per day is considered safe.74
A nationwide study recently reported that 27% of the U.S. population had low blood levels of vitamin E.75 76 77 78 Supplementing with at least 100 IU per day of vitamin E is associated with lowered risk of heart disease, and a double-blind study found that 400 to 800 IU of vitamin E per day reduced the risk of nonfatal heart attacks, but not fatal ones. However, another double-blind trial found no benefit from 400 IU per day of vitamin E supplementation on the risk of non-fatal heart attacks,79 80 A more recent study found that taking large amounts of vitamin E (400 IU per day or more) may result in a small increase in all-cause mortality,81 while another study found that 400 IU per day increased the risk of heart failure.82 Because of these studies, some doctors are advising people not to take large amounts of vitamin E. On the other hand, circumstantial evidence suggests that “mixed tocopherols,” as opposed to the more widely used alpha-tocopherol, may be safer and more beneficial with respect to heart-disease prevention.83 84 A reduced risk of prostate cancer in smokers was reported in a double-blind trial with 50 IU per day of vitamin E.85 However, similar studies have not found vitamin E supplements to protect against other cancers.86 87 88 89 while another study found that 50 IU per day had no effect on heart attack risk.
Vitamin K deficiency severe enough to cause bleeding problems is rare in healthy people. However, low vitamin K in the blood90 91 and in the diet92 has been associated with osteoporosis. Preliminary research has suggested that supplements of at least 1 mg per day of vitamin K reduce indicators of bone loss in some women.93 94 95 96