Older women who use some vitamin or dietary supplements may be increasing their risk of death, according to a study published in the Archives of Internal Medicine today as part of the journal’s Less is More series.
Use of dietary supplements has grown substantially among women in the United States. About 85% of US women reported use of at least 1 such product in 2004 compared with 66% in 1986, according results from the Iowa Women’s Health Study, a survey of more than 40 000 women aged 55 to 66 years. Additionally, use of multiple supplements has become common, with 27% of women reporting using 4 or more such products in 2004.
The new study, which also analyzed data from the Iowa study, suggests there may be harms associated with some dietary supplements. The study found that several supplements were associated with an increased risk of mortality, including multivitamins (increased absolute risk [IAR] of 2.4%), folic acid (IAR of 5.9%), iron (IAR of 3.9%), and copper (IAR of 18%). It also found that calcium supplementation was associated with a reduced risk of death.
Study author Jaakko Mursu, PhD, of the University of Eastern Finland in Kuopio and the School of Public Health at the University of Minnesota in Minneapolis, spoke with JAMA about the study’s results.
news@JAMA: Were you surprised to see an increased risk of death among women using certain supplements?
Dr Mursu: I was a bit surprised to see such a large increase in the risk of mortality, as in most previous studies supplement use has not been associated with increased risk.
news@JAMA: What do you think might be driving an increased risk of death associated with these supplements?
Dr Mursu: We could not address the mechanisms in this study, but it could be related to the fact that most compounds are harmful in high amounts. We doubt that they were driven by behavior, as supplement users tended to have healthier lifestyles.
news@JAMA: You documented a beneficial effect of calcium supplementation. Is there a plausible explanation for such an effect?
Dr Mursu: In previous cohort studies or clinical trials, calcium supplementation has not been found to be beneficial in regard to total or [cardiovascular disease–associated] mortality. We have no good explanation for why, in our study, calcium was related with a reduced risk. We noticed that out of different supplements, calcium use was among the most strongly related with healthy behavior. Another option is that it could be good for bone health and prevented severe fractures. However, we did not address this issue in this study.
news@JAMA: Alternatively, you found an association between iron supplementation and increased mortality, including a dose-dependent response. What might be the mechanism?
Dr Mursu: In some studies, high iron stores have been associated with increased risk of cardiovascular disease, although evidence is not consistent. Iron itself could be toxic and increase oxidative stress. In this study, we could not, however, address this issue.
news@JAMA: What do you think is the main take-home message for women and their physicians?
Dr Mursu: We feel that instead of taking supplements, women should put more emphasis on a healthy diet. At the moment, there is a very little evidence that supplement use would protect against major chronic diseases.