A multivitamin-multimineral supplement can fill inmicronutrient gaps in your diet.
Nearly 40 percent of adults in the U.S. take a multivitamin to ensure good health. (1) A recent study in Iowa women suggests that this daily habit may be doing more harm than good. (2) A closer look, however, reveals major flaws in the study—and offers reassurance that taking a daily multivitamin may still be a smart move.
The precise requirements for various vitamins have been controversial since their discovery in the late 1800s and early 1900s. The early recommendations were based on the amounts needed to avoid so-called diseases of deficiency such as scurvy (too little vitamin C), beri-beri (too little vitamin B1), pellagra (too little vitamin B3), and rickets (too little vitamin D). Ongoing research suggests a broader role for vitamins. Work by Dr. Bruce N. Ames of the University of California, Berkeley, and others shows that deficiencies in many micronutrients can lead to damage to DNA, the essential “blueprint” of each cell. (3) Such damage can cause or accelerate aging-related conditions. (4) This would make chronic conditions such as cancer, heart disease, vision loss, and a host of others a new type of deficiency disease.
Why Take a Multivitamin?
For those who eat a healthy diet, a multivitamin may have little or no benefit. A diet that includes plenty of fruits, vegetables, whole grains, good protein packages, and healthy fats should provide most of the nutrients needed for good health. But not everyone manages to eat a healthful diet. When it comes to micronutrients, many Americans get less than the adequate amounts, according to criteria set by the Institute of Medicine. For example, more than 90 percent of Americans get less than the Estimated Average Requirement for vitamin D and vitamin E from food sources alone. (5) Many older people have trouble absorbing vitamin B12 from food; the Dietary Guidelines for Americans 2010, in fact, recommends that people over the age of 50 eat foods fortified with vitamin B12 or take vitamin B12 supplements. (6)
Getting enough of another B vitamin, folate, is especially important for women who may become pregnant, since adequate folate can help lower the risk of having a baby with spina bifida or anencephaly. For the folate to be effective, it must be taken in the first few weeks of conception, often before a woman knows she is pregnant. Yet in the U.S., half of all pregnancies are unplanned. That’s why the Centers for Disease Control and Prevention recommends that all women of childbearing age (ages 15 to 45) consume 400 micrograms per day of folic acid. (7) And a standard multivitamin that contains the Recommended Dietary Allowance (RDA) for folic acid offers a convenient way to do that.
For these reasons, we believe a daily multivitamin-multimineral pill offers safe, simple micronutrient insurance, and the findings from the latest study don’t change our recommendation.
A Closer Look at Multivitamins and Mortality
The research, which was based on the Iowa Women’s Health Study, looked at the use of 15 supplements, including multivitamins, at three different intervals and identified the numbers of women who died over a 19-year period. It showed that women over the age of 55 who took multivitamins were at higher risk for dying than those who did not. (2) A similar risk was found for other vitamins and minerals, including folate, vitamin B6, iron, magnesium and zinc.
The study is weak for several reasons. For starters, most people die from a prolonged illness and sometimes start to take vitamins after their health deteriorates; they don’t become ill after they start taking vitamins. The Iowa study, however, didn’t exclude women who were sick or take into account how long they were taking supplements. As a result, we have no idea whether the women were already taking vitamins when they became ill, or if they became ill and then started taking vitamins. In women who were already sick, taking vitamins and supplements was unlikely to lower their risk of dying. In addition, the Iowa study found no benefit for vitamin D supplements, which contradicts at least two highly regarded studies showing that vitamin D protects against mortality. (8,9)
The study’s strongest finding was in regards to supplemental iron. It’s clear that taking a high amount of iron can be harmful, especially in women who have trouble regulating iron absorption for genetic reasons. It’s also possible, however, that some women were taking iron for diseases, injuries, or surgeries that cause anemia, and that these underlying health problems—not the iron supplements—made them more vulnerable to dying. We recommend against iron supplements for men or postmenopausal women, unless there is a specific diagnosis of iron deficiency.
What about other studies that appear to show vitamin supplements cause harm? Those studies often suffer from the same flaws as the Iowa study. Take, for example, a frequently-cited analysis of 68 antioxidant supplement trials that was published in the Journal of the American Medical Association. (10) That study found that taking beta carotene and vitamin A and E supplements increased the risk of dying. But most of the studies included in the analysis were done in people who already had some type of serious illness. It was also impossible to compare interventions because the types of supplements, the dosages taken, and the length of time they were taken varied so widely in the studies.
In reality, there is little solid evidence to support the idea that multivitamins or modest doses of individual nutrients increase the risk for major diseases or early death. And many studies show just the opposite—that multivitamin supplements may protect us from major illnesses such as heart disease, and colon and breast cancer. One recent study found that women who took multivitamins for more than 15 years had lower odds of developing colorectal cancer that those who never took multivitamins, and also had lower odds of developing precancerous growths in the large intestine (adenomas). (11) Other studies have shown that adequate folate is associated with lower risks of coronary heart disease. (12) Among women who drink alcohol, multivitamin users also had a lower risk of breast cancer, and folic acid (the synthetic form of folate) from the multivitamins seemed to be responsible for this protection. (13) Both studies on folate were done before foods were fortified with folic acid, which may have made multivitamin supplements even more important.
Of course, high doses of any supplement have the potential to cause harm. Too much iron for instance, can lead to organ damage, especially in men and postmenopausal women who generally do not require iron supplements. The Health Professionals Follow-Up Study also found that men who took high dose zinc supplements (more than 100 milligrams/day), or took zinc supplements for a long period of time, were at greater risk for prostate cancer than men who did not take any zinc supplements. (14) It’s a worrisome finding that merits more investigation. Other prospective studies on zinc supplements have not seen evidence of such harm, however, study participants did not take quite as high doses of zinc. (15) A randomized trial designed to test supplements to prevent eye disease gave participants a slightly lower dose of zinc supplements—80 milligrams/day—and found that taking these supplements reduced the risk of dying. (16)
The Bottom Line: A Daily Multivitamin Is Still Good Nutrition Insurance
Some scientists believe there is not enough evidence to recommend for or against taking a daily multivitamin, because there isn’t yet enough data from randomized controlled trials. (17) That’s a reasonable but short-sighted point of view since it may never be possible to conduct randomized trials that are long enough to test the effects of multiple vitamins on risks of cancers, Alzheimer’s disease, and other degenerative conditions. Looking at all the evidence—from epidemiological studies on diet and health, to biochemical studies on the minute mechanisms of disease—the potential health benefits of taking a standard daily multivitamin appear to outweigh the potential risks for most people. (18)
The good news is, you don’t need an expensive “designer” supplement or a name-brand kind to reap health benefits. A standard store-brand multivitamin-multimineral supplement is fine. Look for one that contains RDA-level amounts and that also has the United States Pharmacopeia (USP) seal of approval on the label. The amount of vitamin D in most such supplements is usually 400 IU, so you might want to look for one that contains 800–1,000 IU of vitamin D or get additional amounts from a separate vitamin D supplement as well. In fact, the desirable intake of vitamin D is shifting swiftly; many people may need 2,000 IU per day (or more) to get their blood levels of vitamin D into an adequate range; particularly if they have darker skin, spend winters at higher latitudes (such as the northern U.S.), or spend little time in the sun. For premenopausal women, a multivitamin that includes the RDA for iron is a good idea.
Knowledge about the optimal intakes of vitamins and minerals is not set in stone. So it will be important to continue researching the relationships between vitamins, minerals, and chronic disease, over decades. This may mean more confusing news headlines along the way, as the science develops. Read these tips on how to be a savvy reader of news articles about vitamin supplements and nutrition.
1. Gahche J, Bailey R, Burt V, et al. Dietary supplement use among U.S. adults has increased since NHANES III (1988–1994). Hyattsville, MD. 2011.
2. Mursu J, Robien K, Harnack LJ, Park K, Jacobs DR, Jr. Dietary Supplements and Mortality Rate in Older Women: The Iowa Women’s Health Study. Arch Intern Med. 2011;171:1625-33.
3. Ames BN, Wakimoto P. Are vitamin and mineral deficiencies a major cancer risk? Nat Rev Cancer. 2002;2:694-704.
4. Ames BN. Low micronutrient intake may accelerate the degenerative diseases of aging through allocation of scarce micronutrients by triage. Proc Natl Acad Sci U S A. 2006;103:17589-94.
5. Fulgoni VL, 3rd, Keast DR, Bailey RL, Dwyer J. Foods, fortificants, and supplements: where do Americans get their nutrients? J Nutr. 2011;141:1847-54.
6. U.S. Department of Agriculture, U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. Washington, D.C.: U.S. Government Printing Office; 2010.
7. Centers for Disease Control and Prevention. Folic Acid Recommendations. Accessed November 14, 2011.
8. Autier P, Gandini S. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Arch Intern Med. 2007;167:1730-7.
9. Bjelakovic G, Gluud LL, Nikolova D, et al. Vitamin D supplementation for prevention of mortality in adults. Cochrane Database Syst Rev. 2011:CD007470.
10. Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA. 2007;297:842-57.
11. Lee JE, Willett WC, Fuchs CS, et al. Folate intake and risk of colorectal cancer and adenoma: modification by time. Am J Clin Nutr. 2011;93:817-25.
12. Rimm EB, Willett WC, Hu FB, et al. Folate and vitamin B6 from diet and supplements in relation to risk of coronary heart disease among women. JAMA. 1998;279:359-64.
13. Zhang S, Hunter DJ, Hankinson SE, et al. A prospective study of folate intake and the risk of breast cancer. JAMA. 1999;281:1632-7.
14. Leitzmann MF, Stampfer MJ, Wu K, Colditz GA, Willett WC, Giovannucci EL. Zinc supplement use and risk of prostate cancer. J Natl Cancer Inst. 2003;95:1004-7.
15. Gonzalez A, Peters U, Lampe JW, White E. Zinc intake from supplements and diet and prostate cancer. Nutr Cancer. 2009;61:206-15.
16. Clemons TE, Kurinij N, Sperduto RD. Associations of mortality with ocular disorders and an intervention of high-dose antioxidants and zinc in the Age-Related Eye Disease Study: AREDS Report No. 13. Arch Ophthalmol. 2004;122:716-26.
17. National Institutes of Health State-of-the-Science Conference Statement: multivitamin/mineral supplements and chronic disease prevention. Am J Clin Nutr. 2007;85:257S-64S.
18. Ames BN, McCann JC, Stampfer MJ, Willett WC. Evidence-based decision making on micronutrients and chronic disease: long-term randomized controlled trials are not enough. Am J Clin Nutr. 2007;86:522-3; author reply 3-4.
The aim of the Harvard School of Public Health Nutrition Source is to provide timely information on diet and nutrition for clinicians, allied health professionals, and the public. The contents of this Web site are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Web site. The information does not mention brand names, nor does it endorse any particular products.