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.