A recent report known as the Iowa Study is out, and the conclusion for older women who take dietary supplements is not good: Several commonly used dietary vitamin and mineral supplements may be associated with increased total mortality risk; this association is strongest with supplemental iron. In contrast to the findings of many studies, calcium is associated with decreased risk.
From the study: Although we cannot rule out benefits of supplements, such as improved quality of life, our study raises a concern regarding their long-term safety
In the United States, the use of dietary supplements has increased substantially during the past several decades, reaching approximately one-half of adults in 2000, with annual sales of more than $20 billion. Sixty-six percent of women participating in the Iowa Women's Health Studyused at least 1 dietary supplement daily in 1986 at an average age of 62 years; in 2004, the proportion increased to 85%. Moreover, 27% of women reported using 4 or more supplemental products in 2004. At the population level, dietary supplements contributed substantially to the total intake of several nutrients, particularly in elderly individuals.
Read more here. http://archinte.jamanetwork.com/article.aspx?articleid=1105975