Victoria J. Drake, Ph.D.
Although there is no standardized definition, a multivitamin/ mineral (MVM) supplement is generally described as a dietary supplement that contains around 100% of the Daily Value (DV) of most vitamins and nutritionally essential minerals. MVM supplements, however, do not contain the DV for some of the essential minerals (e.g., calcium and magnesium) because the resulting pill would be too bulky to swallow. Notably, DVs listed on the supplement label are largely based on outdated recommendations made in 1968 and therefore do not reflect current dietary intake recommendations by the U.S. government—the Recommended Dietary Allowance (RDA) or Adequate Intake (AI) for micronutrients. For a comparison between the DVs and the current recommendations, see the table at right. Although not typically the case, manufacturers may choose to include micronutrients at levels equivalent to current recommendations in their products. Additionally, many companies market gender- and age-specific formulations of MVM supplements.
An estimated one-third of Americans aged one year and older take MVMs—the most popular type of dietary supplement in the United States. Studies have found that MVM supplement use is more prevalent in certain subgroups, including females, non-Hispanic whites, older adults, and individuals with higher education. Some other studies have associated MVM use with people who have generally healthier diets or rate their health as good or excellent. Daily use of a MVM supplement can help fill nutritional gaps and improve micronutrient status. Many Americans are apparently eating sufficient (or excessive) calories while, at the same time, not meeting daily intake recommendations for vitamins and essential minerals. Indeed, select micronutrient inadequacies are quite common in the United States: a national survey (NHANES 2003-2006) found that 60% of the U.S. population do not meet intake recommendations from diet and supplement use for vitamin E, 45% for magnesium, 38% for calcium, 34% for vitamin A, 25% for vitamin C, 8% for vitamin B6, and 8% for zinc. Vitamin D insufficiency is also very common among Americans.
Moreover, micronutrient inadequacies have been documented in other industrialized countries, and multiple micronutrient deficiencies, especially of vitamin A, iodine, iron, and zinc, are widespread in the underdeveloped world. Micronutrient deficiencies have been estimated to affect almost two billion people worldwide. Such nutritional deficiencies can increase susceptibility to infectious diseases but may also increase risk for chronic, age-related diseases, such as cardiovascular disease, osteoporosis, and cancer. Micronutrient deficiencies have further been linked to cognitive dysfunction. Given the fact that many people are not meeting micronutrient intake recommendations, a daily multivitamin/mineral supplement would offer insurance that most micronutrient needs are met.
However, it is not known whether taking a MVM supplement will decrease the risk of chronic disease. A number of observational studies as well as randomized controlled trials (RCTs) have examined the effect of MVMs on reducing the risk of various cancers, cardiovascular conditions, and other diseases, but results are largely conflicting. Inconsistent findings among studies may be partially attributed to variations in MVM supplement composition, as well as dose and duration of use. Additionally, both observational studies (studies in which a group is simply observed over time with no experimental intervention) and RCTs have inherent limitations that make it difficult to determine whether MVM use might help prevent chronic disease. For example, people who volunteer to be part of such studies are commonly healthier than the average person, and some studies have found that those who take MVM supplements have an overall healthier diet and lifestyle than those who do not take MVMs.
Observational studies may be subject to residual confounding if all of the potential confounding variables are not accounted for in the statistical model. Such studies can only detect associations between MVM use and health endpoints rather than establish cause-and-effect relationships. While RCTs are able to establish cause-and-effect associations, they are ill-suited to study the effects of micronutrients. In particular, the placebo group in RCTs of micronutrients is not a true placebo or non-exposed group because a micronutrient-free state does not exist in the body without deficiency disease, and it is obviously not ethical to deprive the control group of essential micronutrients. Additionally, RCTs of MVM supplements are conducted in generally healthy people (as opposed to those with some disease) and thus would likely take years or decades to observe a measurable effect; compliance during such a long-term study is highly problematic. Short-term RCTs that assess DNA damage, inflammation, insulin sensitivity, lipid profile, blood pressure, immune function, or other biomarkers of disease are more practical and may be useful in determining whether MVMs help prevent chronic disease.
While the health effects of MVM supplements are difficult to determine, MVM supplement use is generally considered safe for healthy people. U.S. government regulations, called current good manufacturing practices (CGMPs), ensure that dietary supplements meet quality standards for identity, purity, strength, and composition, as long as supplement manufacturers comply. Although excessive intakes of select micronutrients can be unsafe, the amounts of micronutrients in MVM products approximate the DVs. For most micronutrients, the DV is considerably lower than the tolerable upper intake level (UL)—the highest level of daily intake of a specific nutrient likely to pose no risk of adverse health effects in almost all individuals of a specified age. The Food and Nutrition Board of the Institute of Medicine recommends that the total daily intake of micronutrients—from foods, fortified foods, and supplements—should not exceed the UL. The DV for vitamin A (5,000 IU) is considerably higher than the current RDA (2,333 IU/day for women and 3,000 IU/day for men), and excessive retinol (preformed vitamin A) intakes have been linked with bone fractures in older adults. For these reasons, the Linus Pauling Institute (LPI) recommends that adults take a MVM supplement providing no more than 2,500 IU (750 mcg) of preformed vitamin A, usually labeled as vitamin A acetate or vitamin A palmitate, and no more than 2,500 IU of additional vitamin A as beta-carotene.
Additionally, because men and postmenopausal women are not at risk for iron deficiency and excess iron can have detrimental health effects, LPI recommends that men and postmenopausal women take a MVM supplement without iron. MVM supplements formulated for men or older adults generally do not contain iron, but one must examine the supplement label. Although MVMs are safe for most people, certain drug-nutrient interactions are possible; thus, the use of all nutritional supplements should be discussed with a competent healthcare provider.
According to national surveys, many Americans have inadequate dietary intake of key micronutrients, possibly increasing their risk for age-related diseases, such as osteoporosis, cardiovascular disease, and some forms of cancer. Micronutrient inadequacies may also be associated with impaired immune responses and untoward effects on cognition. Many Americans are apparently consuming an energy-dense diet that is lacking in essential micronutrients. Given the facts that dietary habits are difficult to change and that many people often cannot afford micronutrient-rich fruits and vegetables, the Linus Pauling Institute recommends a daily MVM supplement as nutritional insurance. For information on healthy eating, see the LPI "Rx for Health". Although the specific consequences of chronic micronutrient inadequacies are difficult to document, it is sensible to ensure adequacy for health by taking a daily MVM supplement at low cost and low risk.
Last updated November 2011