University of Minnesota researchers analyzed data from 38,772 women age 55 and older from the Iowa Women’s Health Study. Between 1986 and 2004, the women filled out three surveys, recalling their use of 15 supplements. After statistically adjusting for things such as weight, diet and lifestyle, researchers concluded that calcium was the only supplement associated with reduced mortality. Meanwhile, women who took multivitamins, B6, folic acid, magnesium, zinc and copper were found slightly more likely to have died during the study period. Those who took the most supplemental iron were even more likely to have died.
We asked Victoria Drake, PhD, of the Linus Pauling Institute at Oregon State University, for her take on the study and its findings:
Natural Foods Merchandiser: Overall, what is your impression of this study and its potential limitations?
Victoria Drake, PhD: I found insufficient evidence to support the claims of the authors. This was an observational study (meaning scientists retrospectively looked at data to examine associations between lifestyle factors and outcomes), not a randomized controlled trial (in which people are chosen for a study, given an intervention and followed). Observational studies can generate only hypotheses and cannot determine cause and effect.
NFM: Why not?
VD: Investigators have to adjust for a lot of things that might confuse any potential association—things such as gender, age, body weight and exercise habits. Even though researchers do their best, they can’t account for all such things. Observational studies are also subject to “recall bias.” In this case, there is some question as to whether people remembered and reported their supplement use accurately.
NFM: Do you have other concerns?
VD: People often begin to take supplements as they age or when they are diagnosed with disease. In this study, supplement use increased from almost 62.7 percent in 1986 to 85.1 percent in 2004. It is likely that during this period, some women began to take supplements because they had been diagnosed with disease. It is misleading to blame the supplement—rather than the disease—for their death. Also, this only looked at white post-menopausal women with higher-than-average supplement use. So you cannot generalize any of the results to premenopausal women, men or other ethnic groups.
NFM: What do you make of the findings about supplemental iron? Is it really dangerous?
VD: Most post-menopausal women (who are no longer losing iron via menstruation) and men should not be taking supplemental iron. In excess, iron can accumulate in the body and lead to oxidative stress on tissues. It can do harm. Premenopausal women should take the recommended daily allowance of 18 mg daily.
NFM: Some headlines have suggested multivitamins are dangerous. What do you think?
VD: Due to the points that I raised, I would not agree with that based on this study. Overall, if you look at national surveys, the data indicate that 70 percent of the U.S. population does not meet the estimated average requirement for vitamin D, 60 percent for vitamin E, 45 percent for magnesium, 38 percent for calcium, 34 percent for vitamin A, and 25 percent for vitamin C. Multivitamins are a safe way to fill these gaps.