The October 2011 Archives of Internal Medicine supplement study has been criticized for using observational research data to support its claims. David Jacobs Jr., PhD, co-author of the study and professor of public health at the University of Minnesota, agrees that an observational study is no match for a randomized controlled trial when it comes to proving causal relationships. He also concedes that many of the study participants taking iron were probably doing so to address illness. “I suspect the reason that iron came out as adverse was because the women taking it were actually sicker [than the others],” he says.
But, Jacobs adds, the findings are valuable nonetheless. He notes that people who take supplements are generally more active, better educated and less likely to smoke—all factors that would lead one to assume they would live longer. But once those things were statistically accounted for in the Archives of Internal Medicine study and only supplement use or nonuse remained as a variable to compare, “for several of the [study participants] there was actually significantly excess risk of total mortality and for many of them there was no association [between supplement use and reduced risk of mortality] at all.”
Still, Jacobs stops short of advising women who are already taking supplements to stop. “I am not saying these things are bad for you,” he says. Instead, Jacobs sees the data as one more reason to modify the Dietary Supplement Health and Education Act to require supplement makers to conduct more research.
“The evidence is not all in, but the data we are presenting is not encouraging,” he says. “Now we need to do the research that would definitively tell us: Are supplements good or bad for you?”