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Vitamin Supplements & Death Risk: Beyond The Headline

October 17, 2011

Conclusions drawn from a review of supplement use among over 38,000 women who participated in the Iowa Women's Health Study (IWHS) recently made startling headlines—that the use of multivitamins in general and of vitamin B6, folic acid, iron, magnesium, zinc and copper supplements in particular was associated with an increased risk of death.

The IWHS began in 1986 with over 41,000 postmenopausal women ages 55 to 69 at the start. The primary aims of the study were to determine if the distribution of body fat is a predictor of chronic diseases, including certain cancers, and to what degree diet and other lifestyle factors influence women’s risk of chronic diseases. Periodic questionnaires provided self-reported information—that means that, while the IWHS and many such studies have yielded a wide variety of information, this was not a scientific, controlled research study. The study making headlines last week specifically looked at the women’s supplement use. The participants reported their use of supplements in 1986, 1997 and 2004, usage that increased over the course of nearly two decades: The percentage of women who reported using at least one supplement daily increased from 62.7 percent to 85.1 percent during the study and in 2004, more than one-quarter of the women who replied said they used four or more products. The purpose of the supplement study, which was published in the October 10, 2011 issue of Archives of Internal Medicine, was to look at whether all these nutritional supplements were having a positive effect on health.

Over the duration of the IWHS, about 40 percent of all participants passed away. What was the difference between women who took supplements and those who didn’t? It varied, based on the supplement. Of the 12,769 women in the study who took a daily multivitamin, 40.8 percent died, and of the 10,161 women who hadn't taken a daily multivitamin, 39.8 percent died. That’s a 1 percent difference. Measured as “increased risk of death,” increases in risk ranged from 2.4 percent with multivitamins to 18 percent with copper. Another high-risk mineral was iron, which can be problematic and have side effects, but the researchers don’t know whether participants were taking iron (or other supplements) because had an iron deficiency from a health condition that could have been responsible for their death. Such limitations didn’t allow the researchers to determine if there were specific causes for the increases in mortality. And they noted that their study was further limited by numerous factors, such as the possibility of changes in supplement use during the study and the lack of data on their nutritional status or detailed information on the supplements used. Also, the participants were all white women, which limits whether the findings can be generalized.

While the authors did show the positive effects of taking calcium—a 3.8 percent absolute mortality risk reduction, overall they state that in a well-nourished population, they cannot recommend the use of vitamin and mineral supplements as a preventive measure, that supplements do not replace or add to the benefits of eating fruits and vegetables and that they may cause unwanted health consequences.

The problem for many people, even in highly developed countries like the US, is whether we are eating a diet that’s nutrient rich enough. Quantity isn’t our problem—quality often is. We’re eating too many processed foods that don’t offer vitamins and minerals, and even for those whose diets are rich in fruits and vegetables, whether they retain their nutrients in transit from farm to table is uncertain.
On the flip side, there are legitimate concerns about supplements. For one thing, these products aren’t regulated by the government, and neither their safety nor health claims have to be backed up.
The bottom line: Talk to your doctor about your diet and any possible deficiencies you might have. Key ones to be sure you’re getting are vitamin D, calcium and heart-healthy omega-3 fatty acids (found in fatty fish, walnuts and other foods).