How Do Multivitamin Supplements Affect Lifespan?

A nationally representative sample of thousands of Americans over the age of 60 found that 70 percent reported using dietary supplements. Perhaps that should be 100 percent since the official Institute of Medicine recommendation is that everyone over the age of 50 take supplemental B12 in the form of fortified foods or a supplement. But the most common supplement taken was a multivitamin. What might that do for our lifespan? Those taking multivitamins tend to live longer than those who don’t, but supplement users also tend to be wealthier, higher educated, physically active with a healthier diet, and less likely to be a smoker, heavy drinker, or obese. When you peel away these other factors, the apparent benefits to multivitamin use tend to disappear. There are two nutrients associated with lower mortality even after controlling for these factors—vitamin K and magnesium—but only when restricted to intake from foods, in other words, vegetables. Vitamin K or magnesium supplements didn’t appear to help.

To answer the question once and for all, can’t we just take 15,000 or so people and randomize them to common daily multivitamin like Centrum Silver or a sugar placebo pill for more than a decade and see what happens? That’s exactly what Harvard researchers did, and they found no significant effect on total mortality. Eight other randomized controlled trials of multivitamin/multimineral supplements have been run, randomizing more than 50,000 men and women, average age 62, typically to years of such supplements, and no overall benefit to mortality was found. “[W]e believe that the case is closed,” read an editorial published in the Annals of Internal Medicine entitled “Enough is Enough: Stop Wasting Money on Vitamin and Mineral Supplements.” Instead of trying to get our nutrients from pills, concluded a 2021 review on vitamin and mineral supplements, we should “move to more plant-based diets, as advised now internationally.”

At least multivitamins appear to be safe. The fact that they were not associated with mortality was heralded as good news, after results from the Iowa Women’s Health Study had found multivitamin use was associated with a higher risk of premature death. However, there are a few supplements for which it appears people are actively paying to live a shorter life. Meta-analyses of randomized controlled trials have found high-dose vitamin A, beta carotene, and extended-release niacin all increase mortality risk compared to placebo.

One way supplements could harm more than our wallet is through a fascinating glitch of human psychology called self-licensing. In my video Do Healthy Fast-Food Options Lead to Healthier Choices? I explore how smokers smoke more and dieters eat more when randomized to take quote-unquote “supplements” (that were actually placebos). “Hence,” the investigators concluded, “people who rely on dietary supplements for health protection may pay a hidden price: the curse of licensed self-indulgence.”