According to results from the Iowa Women’s Health Study, use of several common dietary supplements may increase the risk of death. These results were published in the Archives of Internal Medicine.
Dietary supplements such as multivitamins are widely used by the U.S. population in the hope of preventing or treating common chronic diseases. Although the health effects of many dietary supplements remain uncertain, a growing body of evidence suggests that some may cause harm.
To explore the relationship between dietary supplements and risk of death among older women, researchers evaluated information from the Iowa Women’s Health Study. The study, which began in 1986, enrolled more than 38,000 women. The average age of study participants at the start of the study was 62 years.
- Use of dietary supplements increased over the course of the study. In 1986, 63 percent of women reported using at least one dietary supplement. This increased to 75 percent in 1997 and to 85 percent in 2004.
- Women who used the following dietary supplements had an increased risk of death:
- Vitamin B6
- Folic acid
- Of the supplements listed above, iron had the strongest link to increased mortality.
- Calcium supplements appeared to reduce the risk of death.
These results suggest that several commonly used dietary supplements may actually have harmful effects when used by healthy people. This study focused on older women, and it’s uncertain whether the results would apply to younger people or to men.
People who use dietary supplements or who are considering use of dietary supplements are advised to discuss their decision with their physician. Dietary supplements may have an important role in treating people with nutrient deficiencies, but in the absence of strong evidence they should not be assumed to be beneficial (or harmless, for that matter) when used by the general population. People who are receiving treatment for cancer or other medical conditions should also be aware the some supplements can interact with certain medications; supplements should therefore not be used by people in treatment unless their physician has approved it.
An accompanying editorial notes that older women (and perhaps men as well) may benefit taking vitamin D supplements, especially if they get little vitamin D from the sun or food. The possible benefit provided by calcium supplements also warrants additional study.
 Bjelakovic G, Gluud C. Vitamin and Mineral Supplement Use in Relation to All-Cause Mortality in the Iowa Women’s Health Study. Comment on “Dietary Supplements and Mortality Rate in Older Women.” Archives of Internal Medicine. 2011;171:1633-1634.