Taking a daily multivitamin does not help people live longer, but may increase the risk of premature death, a major study has found.

Researchers analyzed the health records of nearly 400,000 adults who had no major long-term illnesses to see whether taking daily multivitamins reduced their risk of death over the next two decades.

Surprisingly, they found that people who took a daily multivitamin were slightly more likely to die during the study period than those who didn’t take multivitamins.

This led the researchers to conclude that “the use of multivitamins for improving longevity is not supported.”

Globally, the market for these supplements is worth billions of dollars each year. In the US, about a third of adults use multivitamins to prevent disease.

Despite their popularity, researchers have questioned the health benefits of multivitamins and even warned that they may be harmful.

For example, while natural food sources of beta-carotene may protect against cancer, beta-carotene supplements may increase the risk of lung cancer and heart disease.

Similarly, the excess iron contained in many multivitamins may increase the risk of heart disease, diabetes, and dementia.

More information about the study

In their study, Dr. Ericka Loftfield of the National Cancer Institute in Maryland and her team examined data from three major U.S. health studies that began in the 1990s.

They tracked 390,124 generally healthy adults for over 20 years and found that taking a daily multivitamin was associated with a reduced risk of death. Instead, they reported that users had a 4% higher risk of death in the early years of follow-up.

This increased risk may be due to the harmful effects of multivitamins or the tendency for people to start taking them when they develop serious illnesses. These findings were published in JAMA Network Open.

The authors write, “Sufficient evidence now indicates that apart from the above roles of vitamin supplementation, there is no health rationale for the use of multivitamin supplements. Micronutrients are most commonly obtained from healthful food sources. When supplementation is needed, it can often be restricted to the micronutrient in question.”