Multivitamins: Ingredients to Avoid
Most studies have not shown a consistent benefit of taking multivitamin/mineral supplements for preventing chronic diseases.1 A 2006 National Institutes of Health (NIH) State-of-the-Science Conference Statement reported regarding studies on multivitamin/mineral supplements and chronic disease prevention “Most of the studies we examined do not provide strong evidence for beneficial health-related effects of supplement…”2
Of course, micronutrient deficiency is detrimental to health. So why have most studies shown no benefit for preventing chronic disease? One important reason is that most multivitamin/mineral supplements on the market contain ingredients that have been shown by studies to be harmful in supplement form.
Certain nutrients are beneficial when provided by whole foods, but may be harmful in supplement form.
- Folic Acid. The synthetic folic acid found in supplements is chemically different from food folate, which is abundant in green vegetables, beans and other plant foods. Folate is especially important for women of childbearing age, to prevent against birth defects. However, women who take synthetic folic acid in multivitamins may be at increased risk of breast cancer.3-8 Folic acid supplementation also raises the risk of prostate and colorectal cancers.9-11 Luckily, we don’t need to get folic acid from vitamins, because folate is plentiful in green vegetables and other whole plant foods. Folate in its natural form protects against breast and prostate cancers.9,12-14 Of course when we get our folate from food it comes naturally packaged in balance with hundreds of other cancer protective micronutrients. Consuming folate-rich foods, not folic acid, during pregnancy may also offer protection against cardiac birth defects, childhood respiratory illnesses, and childhood cancers.15-21
- Vitamin A and Beta-carotene. Ingesting vitamin A or beta-carotene from supplements can potentially increase cancer risk by interfering with the absorption of other carotenoids with anti-cancer properties, like lutein and lycopene.22 Beta-carotene supplements are poor substitutes for the broad assortment of carotenoid compounds found in plants. Since beta-carotene gets converted into vitamin A by the body, there is no reason a person eating a reasonably healthy diet should require any extra vitamin A. There is solid research revealing that supplemental vitamin A induces calcium loss in the urine, contributing to osteoporosis.23 Too much vitamin A from supplements during pregnancy is associated with cardiac birth defects.24 On top of these risks, a recent meta-analysis found an increased risk of mortality in people who took supplemental vitamin A, beta-carotene, or vitamin E. 25
- Vitamin E. As mentioned above, supplemental vitamin E in the dosage ranges higher than what can be achieved with food is associated with an increase in mortality risk. Vitamin E is an antioxidant vitamin that we can easily get from raw nuts and seeds, rather than in a supplement.25
- Selenium. There is evidence that high selenium levels are linked to diabetes, hyperlipidemia, prostate cancer, cardiovascular disease, and impaired immune and thyroid function. The studies are somewhat conflicting though—some see a mild protective effect, and some see a detrimental effect. There is also a link between selenium excess and amyotrophic lateral sclerosis (ALS).26-29 The answer here is to have selenium sufficiency, but be careful not to get excess.
- Iron and copper. Iron and copper serve vital biological functions, but as we age excess amounts of these metals may build up and become toxic. The most common culprits of iron and copper excess are red meat and multivitamins. Iron is crucial for oxygen transport, and both iron and copper are essential for the proper function of several chemical reactions in several of the body’s cells and tissues. The human body evolved to store excess iron and copper to fuel these reactions in case of extreme conditions like bleeding or famine. However, their accumulation over time may be detrimental because both metals are involved in generating oxidative stress, a byproduct of energy production, which contributes to chronic diseases—specifically cardiovascular disease and brain disorders like Alzheimer’s disease. There are appropriate times to supplement with iron, however—when there is a deficiency or an increased biological need, such as in pregnancy.
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2. NIH State-of-the-Science Conference Statement on Multivitamin/Mineral Supplements and Chronic Disease Prevention. NIH Consens State Sci Statements 2006;23:1-30.
3. Charles D, Ness AR, Campbell D, et al: Taking folate in pregnancy and risk of maternal breast cancer. BMJ 2004;329:1375-1376.
4. Stolzenberg-Solomon RZ, Chang SC, Leitzmann MF, et al: Folate intake, alcohol use, and postmenopausal breast cancer risk in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Am J Clin Nutr 2006;83:895-904.
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8. Zhang YF, Shi WW, Gao HF, et al: Folate intake and the risk of breast cancer: a dose-response meta-analysis of prospective studies. PLoS One 2014;9:e100044.
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22. Mayne ST: Beta-carotene, carotenoids, and disease prevention in humans. FASEB J 1996;10:690-701.
23. Melhus H, Michaelsson K, Kindmark A, et al: Excessive dietary intake of vitamin A is associated with reduced bone mineral density and increased risk for hip fracture. Ann Intern Med 1998;129:770-778.
24. Botto LD, Loffredo C, Scanlon KS, et al: Vitamin A and cardiac outflow tract defects. Epidemiology 2001;12:491-496.
25. Bjelakovic G, Nikolova D, Gluud LL, et al: Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2008:CD007176.
26. Vinceti M, Wei ET, Malagoli C, et al: Adverse health effects of selenium in humans. Rev Environ Health 2001;16:233-251.
27. Mueller AS, Mueller K, Wolf NM, et al: Selenium and diabetes: an enigma? Free Radic Res 2009;43:1029-1059.
28. Navas-Acien A, Bleys J, Guallar E: Selenium intake and cardiovascular risk: what is new? Curr Opin Lipidol 2008;19:43-49.
29. Chan JM, Oh WK, Xie W, et al: Plasma selenium, manganese superoxide dismutase, and intermediate- or high-risk prostate cancer. J Clin Oncol 2009;27:3577-3583.