Taking dietary supplements will not extend life, researchers report, and taken in large quantities may even be harmful.
In a study in the Annals of Internal Medicine, scientists gathered dietary information in repeated in-person interviews with almost 31,000 men and women 20 and older.
They also collected data on supplements used over the previous 30 days, including type, dosage and frequency of use. Slightly more than half the participants took supplements, and about a third took multivitamins.
Over six years, there were 3,613 deaths, including 945 from cardiovascular disease and 805 from cancer. Over all, after adjustment for other health and behavioral characteristics, they found that using any dietary supplements had no effect on mortality. Adequate intakes of vitamins A and K, magnesium, zinc and copper were associated with reductions in all-cause mortality, but only when the substances came from food, not supplements.
Taking 1,000 or more milligrams of calcium a day was associated with an increased risk for death from cancer, and vitamin D supplements in doses above 400 IU a day were associated with increased cancer death and death from any cause.
“Dietary supplements are not a substitute for a healthy balanced diet,” said the senior author, Dr. Fang Fang Zhang, an associate professor of epidemiology at the Friedman School of Nutrition Science and Policy at Tufts University. “We should aim for adequate nutrition through diet rather than counting on supplements.”