Some vitamins, mineral supplements may be harmful

Several commonly used vitamin and mineral supplements were significantly associated with increased total mortality risk in 38,772 older women from the Iowa Women’s Health Study who were followed for a mean of 19 years.

Supplemental iron was most strongly associated with increased mortality (hazard ration of 1.10 in a fully adjusted model). Of the University of Eastern Finland, Kuopio, and colleagues reported.

The use of multivitamins, vitamin B6, folic acid, magnesium, zinc, and copper also was associated with a higher risk of mortality (hazard ratios, 1.06, 1.10, 1.15, 1.08, 1.08 and 1.45, respectively) after adjustment for age, education level, place of residence, diabetes mellitus, high blood pressure, body mass index, waist to hip ratio, hormone therapy, physical activity, smoking status, alcohol intake, energy intake, saturated fatty acids intake, whole grain products intake, and fruit and vegetable intake.

Conversely — and in contrast to findings from some prior studies — calcium supplementation was associated with decreased mortality risk in adjusted models (hazard ratio of 0.91 for the fully adjusted model), the investigators found.

Participants in the Iowa Women’s Health Study were enrolled in 1986 and those included in the current study had a mean age of 62 years. Participants completed a 16-page self-administered questionnaire that included information on food frequency and supplement use. Additional self-reports were provided in 1997 and 2004. As of Dec. 31, 2008, 40% of those included in the analysis had died.

Self-reported supplement use increased over time, with 63%, 75%, and 85% reporting the use of at least one supplement daily in the 1986, 1997, and 2004 questionnaires, respectively.

On analysis performed for shorter follow-up intervals of 10, 6, and 4 years, the findings for iron and calcium were replicated; about 15% of the deaths in original participants occurred in each of the following periods: 1986 through 1996, 1997 through 2003, and 2004 through 2008.

“In the multivariable adjusted analyses across the shorter follow-up intervals, beginning with the baseline and each follow-up questionnaire, the most consistent findings . . . were for supplemental iron (hazard ratios 1.20, 1.43 and 1.56 . . .) and calcium (0.89, 0.90, 0.88),” the investigators said.

Furthermore, increased consistency of use of iron was associated with increased mortality (versus non-use) for those who reported using iron at only one survey was 1.35, compared with 1.62 and 1.60 for use at two and at all three surveys, respectively.