Although the consumption of dietary supplements has increased considerably over the past decade, most of these products do not reduce total mortality in older women, and many appear to be associated with increased mortality risk (Arch Intern Med. 2011;171:1625-1633). 

The use of vitamin and mineral supplements in relation to total mortality was assessed based on data from 38,772 older participants (mean age 61.6 years at baseline in 1986) in the Iowa Women’s Health Study. Supplement use was self-reported in 1986, 1997 and 2004. Consumption rose substantially throughout that that time frame, with 62.7% of women taking at least one supplement daily in 1986, compared with 75.1% in 1997 and 85.1% in 2004. 

A total of 15,594 deaths (40.2%) occurred by December 31, 2008 (mean follow-up 19 years). The investigators calculated that most supplements did not reduce mortality in this population, and that the use of multivitamins, vitamin B6, folic acid, iron, magnesium, zinc and copper were associated with increased risk of total mortality when compared with corresponding nonuse. The association was strongest with supplemental iron. The use of calcium supplements, however, was associated with reduced mortality risk.

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The findings for both the iron and the calcium supplements were replicated in separate, short-term analyses with follow-up occurring at four, six and 10 years. 

The results provide little justification for the general and widespread use of dietary supplements, according to the authors, who recommend that these products be used with strong medically based cause, such as symptomatic nutrient deficiency disease.