Dietary Supplements and Mortality Rates in Women: A Cautionary Tale

JoAnn E. Manson, MD, DrPH


November 15, 2011

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Hello. This is Dr. JoAnn Manson, Professor of Medicine at Harvard Medical School and Brigham and Women's Hospital. I would like to talk with you today about an article that was published a few weeks ago in Archives of Internal Medicine[1] about dietary supplements of vitamins and minerals and mortality rates in women.

This report serves as a cautionary tale about the potential risks related to dietary supplements and makes the point that more is not necessarily better. In the United States, about 50% of adults are currently taking 1 or more dietary supplements, and it is a $20-plus billion annual industry. But are consumers really getting value for the money spent?

For a long time, vitamins and minerals had the reputation of being "magic bullets" because they are very effective in treating deficiencies. We know that vitamin C prevents scurvy, vitamin D prevents rickets, and thiamine will prevent beriberi. However, this doesn't mean that in a well-nourished population, these supplements will prevent the chronic diseases, cardiovascular diseases, cancer, and other chronic diseases of the 20th and 21st centuries, or that more will be better.

In this study, the Iowa Women's Health Study, more than 38,000 women who were, on average, age 62, were followed for up to 22 years. There were more than 15,000 deaths during the follow-up period. This study showed very few benefits of any of these vitamin or mineral supplements. In fact, there was a suggestion of some risk associated with several of them.

Multivitamins, vitamin B6, folic acid, iron supplements, copper, and zinc were all associated with some increase in risk. In replication analyses in later follow-up periods, excess risks continued to be seen with iron supplements. This risk was dose-dependent and has been found in some other studies as well. On the benefit side was a suggestion of a reduced risk, or a slight reduction in mortality risk, with calcium supplements.

We know from randomized trials that many of the antioxidant vitamins may, in fact, increase risks, especially in well-nourished populations. The randomized trials of beta-carotene and vitamin E have not shown clear health benefits. Studies even suggested a risk. We know that beta-carotene increases lung cancer risk in smokers, and vitamin E was recently linked to an increased risk for prostate cancer in men and was previously linked to an increased risk for hemorrhagic stroke.

Well-nourished populations may derive no benefits from these supplements, and there may, in fact, be a risk. The bottom line of this report is to try to avoid excessive intake of these micronutrients and to let our patients know that more is not necessarily better. As with many nutrients, there appears to be a U-shaped curve where risk is increased with low-intake deficiency states as well as with high intake. It is probably best to encourage a healthy and balanced diet with a high intake of fruits, vegetables, and whole grains.

The Institute of Medicine has recommended up to 600 IUs of vitamin D for women up to age 70 years and 800 IUs above age 70 years and 1200 mg of calcium daily for postmenopausal women. Some women may need to take supplements in order to achieve these levels of intake. For most vitamins and minerals, a balanced diet will provide adequate intake.

Thank you very much for listening. This is Dr. JoAnn Manson.


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