Some dietary supplements may be associated with an increased risk of death for older women, even though those women tended to be healthier than those who did not take vitamins while alive, according to a study released Monday from the Archives of Internal Medicine.
In analysis of about 39,000 women who were at an average age of 62 at the beginning of the study, those who took vitamin supplements such as multivitamins, vitamin B6, folic acid, magnesium, zinc, copper and iron died at a higher rate during the 19-year research period, researchers led by a team at the University of Minnesota report.
This paper contributes to the growing amount of studies showing no benefits for supplement use in the prevention of chronic diseases, Jaakko Mursu, a postdoctoral researcher in nutrition at the University of Minnesota's School of Public Health and lead author of the study, told the Los Angeles Times.
Of the 15 supplements targeted by researchers, only calcium was reportedly associated with a lower risk of death.
Iowa Data Set
The research data came from the Iowa Women's Health Study, a study that aimed to analyze factors related to cancer that began in 1986. Participants initially filled out health questionnaires -- which included information about diet and vitamin use -- on multiple occasions during the course of the study.
At the beginning of the study, 65 percent of the women reported taking at least one supplement a day. Researchers report that the women who took vitamins at the beginning of the study tended to be more educated, consumed healthier food and were more likely to have an active lifestyle, compared to those who did not.
By 1997, 75 percent of the participants were taking at least one supplement per day and by 2004, 85 percent were doing so. Researchers looked at how many vitamins each participant was taking in 1986, 1997 and 2004 and then cross-checked those numbers with death records to see how the rate of consumption influenced mortality. Ultimately, they found that after adjusting for a respondents' age, background and eating habits, those who consistently took multivitamins had a 2.4 percent increased risk of death. Moreover, those who took zinc were 3 percent more likely to have died and folic acid was linked to a 5.9 percent absolute risk increase.
Iron, a popular supplement for women, was also signaled it out.
Of particular concern, supplemental iron was strongly and dose dependently associated with increased total mortality risk, the report said. However, scientists pointed out the higher mortality rate could also be connected with ailment that those women were taking iron supplements to treat.
Researchers reported that the women who took supplements tended to have lower rates of diabetes, high blood pressure and a lower body mass index than those who did not, even though they seemed to die at slightly higher rates. The study did not investigate where the supplements directly contributed to the causes of death among the participants.
While dietary supplements are not intended to be a substitute from the nutritional benefits received through whole foods such as fruits, vegetables and whole grains, the Mayo Clinic reports that those who do not consistently eat enough healthy foods may benefit from taking a multivitamin.
Some supplements may even have lifesaving properties. Multiple studies have shown that consuming large doses of both vitamin C and vitamin D may help prevent some cancers and inhibit the growth of certain tumors. However, accredited medical texts assert there is no conclusive evidence to prove those supplements are effective in preventing or treating cancer.
Still, some physicians say there is no need for anyone to throw out their multivitamins based on the most recent study.
I wouldn't recommend anyone change what they're doing based on this study, Dr. David Heber, director of the University of California at Los Angeles Center for Human Nutrition, told the LA Times. It's very hard to conclude cause and effect.