When an Op Ed in The New York Times in June 2013 warned readers, “Don’t Take Your Vitamins,” it wasn’t referring to multivitamins like Centrum or One A Day. Instead, Philadelphia physician Paul Offit cautioned that high doses of antioxidants like vitamin E and beta-carotene could raise the risk of cancer and heart disease.
“I think multivitamins don’t hurt you,” Offit told CNN, though he added that he didn’t believe people needed a multi.
The Mayo Clinic had a different take. In a large study of older Midwestern women, noted Mayo’s column in the Chicago Tribune in January 2013, “taking a multivitamin appeared to increase risk of premature death.”
In the Iowa Women’s Health Study, those who reported taking a daily multivitamin were 6 percent more likely to die over a 19-year period than those who said that they didn’t take a multi.
“You want to be very careful in interpreting the results from observational studies,” cautions Eric Jacobs, an epidemiologist at the American Cancer Society in Atlanta.
An observational study watches people. In the Iowa Women’s Health Study, for example, researchers gave the women a questionnaire asking what they ate, how often they exercised, what supplements they took, and more. Then the researchers waited for 19 years to see which women got which diseases or died.
But an observational study can’t tell whether taking a multi caused any illness or death. Those who chose to take a multivitamin may have differed in some way from those who didn’t take a multi.
“Sometimes people start taking multivitamins because they feel sick or low in energy,” notes Jacobs. “They may be more likely to die prematurely for reasons unrelated to their multivitamin use.”
Or the opposite can happen. “Multivitamin users tend to have healthier lifestyles,” says Jacobs. “So if they have a lower risk of disease, that may be the reason, not their multivitamin use.”
To get at cause and effect, researchers randomly assign people to take either a multivitamin or a lookalike but inactive placebo. Since all the people are drawn from the same pool, the only difference between the groups in a randomized controlled trial is that one is taking a multi and one isn’t.
“Randomized controlled trials are a better way of judging the impact of taking a multivitamin,” says Jacobs.
In the largest and longest randomized controlled trial of multivitamins, the Physicians’ Health Study II, more than 14,000 men took either Centrum Silver (a basic multivitamin-and-mineral for people 50 and older) or a placebo every day for 11 years.
“The risk of dying was not significantly different between men taking multivitamins versus men taking the placebo,” says Harvard epidemiologist Howard Sesso, who led the study.
Sources: Arch. Intern. Med. 171: 1625, 2011; JAMA 308: 1871, 2012; JAMA 308: 1751, 2012.
Other relevant links:
- Research suggests multivitamins may not prevent colds. See: Can Multivitamins Prevent a Cold?
- Can a multivitamin protect against disease? See: Multivitamins as cheap insurance for an inadequate diet
- Our list of the best multivitamins. See: The Best Multis