Earlier this week, I was innocently scrolling through the latest research on the JAMA Internal Medicine website. The top headline on the ‘Most Read’ side panel instantly caught my eye: ‘Dietary Supplements and Mortality Rate in Older Women’. Reading, I was amazed to find that taking multivitamins, vitamin B6, folic acid, magnesium, zinc, copper, and in particular iron supplements were all associated with increased risk of death in this study (1). Even more of a surprise, the research was dated from 2011. Why was this not more widely publicized between then and now? A quick Google search ruled out the possibility that I have been deaf to a roaring thunder of anti-vitamin sentiment, as there is little news reporting on potential adverse effects of vitamin supplements.
Before the question of why this topic hasn’t been well-publicized comes the underlying question of whether taking vitamin and mineral supplements truly increases risk of death.
Asking this question is a bit like asking what causes obesity – research can tell us a lot, but it also makes us aware of how little we know, and how clumsy and flawed we humans are when attempting to uncover truths through science. The JAMA Internal Medicine study was the Iowa Women’s Health Study, which investigated the risk of mortality attributed to taking several common types of multivitamin, vitamin, and mineral supplements among 38,772 older women (1). In this study, supplement use was self-reported from memory, which notoriously and tragically often fails even the best of us. The food questionnaire used in the study was well-developed, tested, and validated – it is one of the best tools we have to efficiently assess dietary patterns in large groups of people – but it is not perfect. Incorrect recall, if randomly distributed in the study sample, adds noise to the data to give us null results. Also, are we confident that the biological effect of vitamin supplements in white, post-menopausal women is the same across people of other ages, genders, and races?
The ‘sick-user’ effect – another explanation?
Perhaps another explanation for the mortality effect is that sicker people more commonly take vitamin and mineral supplements than healthy people. In the Iowa Women’s Health Study, the researchers statistically accounted for several healthy behaviors such as physical activity and smoking, and some health problems such as diabetes and high blood pressure. After ruling out these factors that could impact both of whether or not someone takes supplements and their likelihood of dying, there was still an effect of supplements on mortality risk (1). Again, not being perfect, the authors could not account for many other health conditions. A ‘sick-user’ effect may be what we’re seeing in these studies of vitamin and mineral supplementation and mortality (2). It’s also been seen in studies of alcohol and health, where people who drink moderately are often actually healthier than complete abstainers, who sometimes have health problems that preclude them from drinking (3).
Holding the evidence in balance
As always, we have to look at the balance of the research to make decision about causality. In addition to the Iowa Women’s Health Study, a body of high-quality research indicates that a range of dietary supplements have either no effect whatsoever or a small increased effect on mortality risk (1,2,4-6). Importantly, in April 2014, the U.S. Preventive Services Task Force recently released a new recommendation statement regarding vitamin, mineral, and multivitamin supplements for the primary prevention of cardiovascular disease and cancer (7). The Task Force concluded that ‘current evidence is insufficient to assess the balance of benefits and harms of the use of multivitamins for the prevention of cardiovascular disease or cancer’ (7). They also recommended against the use of beta-carotene or vitamin E supplements for the prevention of cardiovascular disease or cancer. Beta-carotene has been found to increase the risk of lung cancer among smokers.
What’s the conclusion?
The American Heart Association recommends that healthy people get adequate nutrients by eating a variety of foods in moderation, rather than by taking supplements (8). They emphasize that:
Vitamin or mineral supplements aren’t a substitute for a balanced, nutritious diet that limits excess calories, saturated fat, trans fat, sodium and dietary cholesterol.
It seems that if you have no nutritional need for a particular vitamin or mineral, then it’s best to hold off on consuming extra. Of course, if you have a concern about your own health, then definitely talk to your doctor. In cases of malnutrition, vitamin and mineral supplementation is a whole other story; this is more of an issue in the developing world.
Should we be told more than we are?
Coming full circle, it is curious that the media hasn’t well-covered the adverse health effects of vitamin supplements. There have been informative reports here and there, but nothing like the media storm that has come after other health discoveries. Given that multivitamins are the most commonly used supplement in the developed world (2), we should reduce (read: stop) our intake to match the seeming fact that they don’t help us prevent two of our biggest killers, cardiovascular disease and cancer, or death itself. The medical community seems to have reached this conclusion, why is it not more widely spread in the public? Let’s not forget that the business of supplementation is just that – a business that aims to make money. An unescapable facet of public health is that we lumber forward with our scientific methods in an inescapable fight against powerful industries that produce the conditions in which ill-health forms and is reproduced. Let’s hope that science outweighs industry in this case to improve the public’s health.
- Mursu J, Robien K, Harnack LJ, Park K, Jacobs DR. Dietary supplements and mortality rate in older women: The Iowa Women’s Health Study. JAMA Intern Med 2011;171(18):1625-1633.
- Li K, Kaaks R, Linseisen J, Rohrmann S. Vitamin/mineral supplementation and cancer, cardiovascular, and all-cause mortality in a German prospective cohort (EPIC-Heidelberg). Eur J Nutr 2012;51(4):407-13.
- Ng Fat L, Cable N, Marmot MG, Shelton N. Persistent long-standing illness and non-drinking over time, implications for the use of lifetime abstainers as a control group. J Epidemiol Community Health 2014;68(1):71-7.
- Macpherson H, Pipingas A, Pase MP. Multivitamin-multimineral supplementation and mortality: a meta-analysis of randomized controlled trials. Am J Clin Nutr 2013;97(2):437-44.
- Watkins ML, Erickson JD, Thun MJ, Mulinare J, Heath CW. Multivitamin use and mortality in a large prospective study. Am J Epidemiol 2000;152(2):149-62.
- Guallar E, Stranges S, Mulrow G, Appel LJ, Miller III, ER. Enough is enough: stop wasting money on vitamin and mineral supplements. Ann Intern Med 2013;159(12):850-51.
- U.S. Preventive Services Task Force. Vitamin, mineral, and multivitamin supplements for the primary prevention of cardiovascular disease and cancer. http://www.uspreventiveservicestaskforce.org/uspstf14/vitasupp/vitasuppfinalrs.htm (accessed 20 August 2014).
- American Heart Association. Vitamin and mineral supplements. http://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/Vitamin-and-Mineral-Supplements_UCM_306033_Article.jsp (accessed 20 August 2014).