The study in question took a look at risk of multivitamin use and mortality in 38,772 women from the Iowa Women’s Health Study (1). Women were asked via questionnaire if they were using any supplements and if they were to describe what they were taking and how often. This question was asked 3 different times over a mean follow-up of 19 years. This was done to reflect changes in supplement use over the years. Women taking a multivitamin had a 6% increased risk of mortality when compared to women who did not take a multivitamin. Here are some of the other interesting findings of this investigation:
B6 supplements were associated with a 10% increased risk of death.
Folic acid supplements were associated with a 15% increased risk of death.
Iron supplements were associated with a 10% increased risk of death.
Magnesium supplements were associated with an 8% increased risk of death.
Zinc supplements were associated with an 8% increased risk of death.
Copper supplements were associated with a 45% increased risk of death.
Calcium supplements were associated with an 8% decreased risk of death.
Was this study methodologically sound?
Overall, this study had a sound methodology. There was a very large sample size, updated measures of supplement use to reflect changes over time, an adequate follow-up and good control of potential confounders. However, this study had one major flaw: the researchers didn’t exclude sick women. This is a major problem because someone who gets diagnosed with a serious medical condition is much more likely to initiate multivitamin use. God forbid you were diagnosed with cancer today; wouldn’t you want to load up on vitamins and supplements to help treat your disease?
This oversight is problematic because many of those who are diagnosed with these serious diseases will die from them. This makes it look like people who are supplementing are dying at a higher rate when in fact, they were sicker from the start. You can eliminate this problem by excluding people who sick at the beginning of your study.
Previous ResearchThere are a number of well designed studies in recent years that have shown a benefit with multivitamin supplementation. These studies show that multivitamins help reduce the risk of coronary heart disease, colon cancer and breast cancer. Vitamin D supplementation is showing a lot of promise and folate supplementation has done much to reduce the incidence of neural tube defect in pregnant women. We can’t forget these positive outcomes when assessing the benefits and risks of multivitamin supplementation.
So What’s The Bottom Line?There has been a good amount of research that shows a benefit to multivitamin supplementation and just a few studies that show potential harm. Considering that there were methodological flaws in some of the research that showed harm, I feel that the benefits of multivitamin supplementation outweigh the risks for most people. However, to hedge your bets, I recommend taking a good multivitamin (which includes vitamin D) every other day. This way you are minimizing the risk while retaining the benefit. This is what I do myself and what I recommend to my clients. Always keep in mind that any kind of supplement will never replace a healthy diet.
References1) Mursu J, Robien K, Harnack LJ, et at. Dietary supplements and mortality rate in older women. Archives of Internal Medicine 2011; 171(18):1625-1633.