Although dietary supplements are commonly taken to avoid chronic disease, long-term health consequences of many compounds are unknown.
We assessed the use of vitamin and mineral supplements in relation to total mortality in 38 772 older women in the Iowa Women's Health Study, mean age 61.6 years at baseline in 1986. Supplement use was self-reported in 1986, 1997 and 2004. Through December 31, 2008, 15 594 deaths (40.2%) were identified through the State Health Registry of Iowa and the National Death Index.
In multivariable adjusted proportional hazards regression models, the use of multivitamins (Hazard Ratio (HR), 1.06 [95% CI, 1.02-1.10], Absolute Risk Increase (ARI), 2.4%), vitamin B6 (HR, 1.10 [95% CI, 1.01-1.21], ARI, 4.1%), folic acid (HR, 1.15 [95% CI, 1.00-1.32], ARI, 5.9%), iron (HR, 1.10 [95% CI, 1.03-1.17], ARI, 3.9%), magnesium (HR, 1.08 [95% CI, 1.01-1.15], ARI, 3.6%), zinc (HR, 1.08 [95% CI, 1.01-1.15], ARI, 3.0%) and copper (HR, 1.45 [95% CI, 1.20-1.75], ARI, 18.0%) were associated with increased risk of total mortality when compared with corresponding nonusers, while calcium was inversely related (HR, 0.91 [95% CI, 0.88-0.94], Absolute Risk Reduction (ARR), 3.8%). Findings for iron and calcium were replicated in separate shorter-term analyses (10-year, 6-year and 4-year follow-up) each with about 15% dead, starting in 1986, 1997, and 2004.
In older women several commonly used dietary vitamin and mineral supplements may be associated with increased total mortality risk, most strongly supplemental iron, while calcium, in contrast to many studies, was associated with decreased risk.