Dietary supplements don’t extend life and might actually shorten it if taken at high levels, researchers reported Monday in the Annals of Internal Medicine. While certain nutrients may contribute to a longer life, they need to come from a food source, the study found.
At a time when more celebrities, social media influencers and wellness websites sell concoctions of vitamins, the new findings join a growing body of evidence that supplements don't help most people. A 2018 study from the University of Birmingham had found multivitamins and mineral supplements didn’t protect against heart disease.
“Based on the totality of evidence, it’s becoming more and more clear that the regular use of dietary supplements is not beneficial in reducing the risk of mortality among the general population in the U.S.,” said study coauthor Dr. Fang Fang Zhang, an associate professor at the Friedman School of Nutrition Science and Policy at Tufts University. “But, we need more research to look at long-term use of supplements. It would also be worth exploring whether supplements might be helpful among those who have nutritional deficiencies.”
With more than half of U.S. adults using dietary supplements, Zhang and her colleagues explored their effects, as well as the impact of nutrients found in foods, with data from 27,725 adults participating in the National Health and Nutrition Examination Survey. All participants were 20 or older when they signed on to be part of the NHANES.
The participants included in Zhang’s study all had filled out a 24-hour food questionnaire twice. In addition, during a household interview, they answered whether they had used any dietary supplements in the previous 30 days. Those who said they had used supplements were asked for details, including how often they took the products.
More than half of the study participants reported using dietary supplements in the previous 30 days and 38.3 percent reported using multivitamin and mineral supplements.
Intriguingly, supplement users were more likely than others to have higher levels of education and family income, eat a healthy diet and be physically active. Those factors are “already known to reduce mortality,” Zhang said.
During the median follow-up of six years, 3,613 of the study participants died. That number included 945 cardiovascular deaths and 805 cancer deaths.
Zhang and her colleagues found a lower risk of death from any cause among those who consumed adequate amounts of vitamin K and magnesium, and a lower risk of cardiovascular death among those with adequate intakes of vitamin A, vitamin K and zinc. Excess consumption of calcium was associated with a higher risk of death from cancer.
I don’t think you can undo the effect of a bad diet by taking supplements.
Food sources of vitamin K include leafy greens such as kale, spinach and broccoli rabe. Zinc is found in beans and legumes, such as lentils and chickpeas. Eggs, as well as orange and yellow fruits and vegetables are high in vitamin A.
The researchers did find a lower risk of death associated with supplements, but that association became non-significant when they accounted for lifestyle factors such as education, smoking and drinking.
The association between a lower risk of death and nutrients consumed in foods remained significant even after those factors were accounted for.
One thing that the researchers cannot say is whether the association is between the nutrients themselves or other components in the foods, Zhang said. And ultimately, the research has found only associations and does not prove that certain nutrients in foods lengthen life.
Dr. Rekha Kumar, an endocrinologist, wasn’t surprised by the finding that people consuming healthy diets lived longer and that supplements didn’t seem to extend life.
“I don’t think you can undo the effect of a bad diet by taking supplements,” said Kumar, an assistant professor of medicine at NewYork-Presbyterian and Weill Cornell Medicine.
As for the finding that high levels of calcium might shorten life, Kumar advises people to get as much calcium from their diet as possible. "If you realize you have a deficit, then supplement, but not more than the recommended daily allowance,” she said.
Most people who take supplements probably aren't expecting to live longer, but hoping for more immediate results, Kumar suggested.
“It’s more likely to be someone looking for more energy and vitality or trying to treat symptoms such as hair loss or leg cramps,” she said.
The message to take from the new study, “even though it’s not glamorous, is to focus on getting our nutrients from our diet rather than from supplements,” Kelly Sanna-Gouin, a registered dietitian at the Detroit Medical Center, said. Nutrients found in foods “can protect us from diseases, so focus on your diet rather than buying supplements.”