Although dietary supplements are commonly taken to prevent chronic disease, the 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 was 61.6 years at
baseline in 1986. Supplement use was self-reported in 1986, 1997, and 2004. Through
December 31, 2008, a total of 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, 1.06; 95% CI, 1.02-1.10; absolute risk increase, 2.4%), vitamin B(6)
(1.10; 1.01-1.21; 4.1%), folic acid (1.15; 1.00-1.32; 5.9%), iron (1.10; 1.03-1.17;
3.9%), magnesium (1.08; 1.01-1.15; 3.6%), zinc (1.08; 1.01-1.15; 3.0%), and copper
(1.45; 1.20-1.75; 18.0%) were associated with increased risk of total mortality when
compared with corresponding nonuse. Use of calcium was inversely related (hazard ratio,
0.91; 95% confidence interval, 0.88-0.94; absolute risk reduction, 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 approximately 15% of the original participants
having died, 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; this association is strongest with
supplemental iron. In contrast to the findings of many studies, calcium is associated
with decreased risk.