Dietary supplements, including daily vitamins, have been a part of life in United States for decades. In fact, people spend $30 billion per year on various pills, powders, gummies and tinctures to help improve their health, boost their brain, lose weight, build muscle and strengthen their immune system.
But a new extensive study suggests many people may be better off spending all that disposable income at the farmer’s market or grocery store produce section to buy spinach, tomatoes and other vitamin-packed veggies instead, according to a paper published this week in the journal Annals of Internal Medicine.
Researchers analyzed data from 27,725 participants in the Centers for Disease Control’s National Health and Nutrition Examination Survey (NHANES). Each volunteer, all over the age of 20, logged what they ate for 24 hours and what supplements they took in the previous 30 days. The data was collected between 1999 and 2010.
Linda Carroll at NBC News reports that during the study's six-year follow-up period, 3,613 participants died, including 945 from cardiovascular disease and 805 from cancer. Using that data, the study team found that getting enough vitamin K—found in leafy greens—and magnesium—found in legumes, nuts, whole grains, fish and meat—were associated with a lower mortality rate. Getting the recommended dose of vitamin K, zinc and vitamin A was linked to lower mortality rates associated with cardiovascular disease.
And it turned out that taking 1,000 milligrams of calcium per day in supplement form was associated with increased cancer risk, while getting excess calcium from food did not seem to increase those risks.
“Our results support the idea that, while supplement use contributes to an increased level of total nutrient intake, there are beneficial associations with nutrients from foods that aren’t seen with supplements,” Fang Fang Zhang of Tufts University, the study’s senior author, says in a statement. “This study also confirms the importance of identifying the nutrient source when evaluating mortality outcomes.”
At first glance, the data suggested that supplement users might have better outcomes than non-vitamin takers. But Beth Mole at Ars Technica reports that supplement users tend to be wealthier and more educated than non-users, smoke less, exercise more, and have an overall healthier diet. When those factors were accounted for, the benefits of supplements disappeared. (It’s possible that supplements are helpful for portions of the population that suffer from certain nutritional deficiencies.)
The study has some limitations. Mole reports that the NHANES data relies on participants self-reporting what they eat and what supplements they take, which means the data might not be entirely accurate. The study is observational, meaning any relationship between nutrients in food and certain diseases is merely an association and does not imply causation.
Still, the study's overall message is that supplements are not a silver bullet for health.
“I don’t think you can undo the effect of a bad diet by taking supplements,” Rekha Kumar, an endocrinologist at NewYork-Presbyterian and Weill Cornell Medicine, who was not involved in the study tells NBC’s Carroll.
This isn’t the first study to question the power of nutritional supplements. A paper last year in the Journal of the American College of Cardiology found that using multivitamins did not provide any apparent benefits but did not cause any harm either.
In fact, taking some supplements have negative consequences. A 2011 study found that taking vitamin E, which was hypothesized to help prevent prostate cancer, actually increased the chances of developing the disease in men instead.
Zhang and her colleagues say that much more research needs to be undertaken to confirm and understand these findings since there are so many other factors that play a role in overall health.