LOS ANGELES — If you’re taking a multivitamin to help you live longer, a new study by researchers at the National Cancer Institute may prompt you to reconsider.
After analyzing health and nutrition data from nearly 400,000 Americans, the researchers found that people who took multivitamins had a small but significantly greater risk of premature death than people who eschewed the supplements.
The findings, reported Wednesday in the journal JAMA Network Open, may seem baffling. Americans aren’t known for having the most balanced diets, and swallowing a pill to fill in our nutrition gaps is often touted as a sensible insurance policy.
Besides, vitamins are essential. It would stand to reason that the more you take, the better. But like so many things regarding our health, the science is not so straightforward.
As recently as 2022, the experts on the U.S. Preventive Services Task Force conducted a thorough review of the medical literature regarding the potential for multivitamins to help prevent cardiovascular disease and cancer. They concluded there was not enough reliable evidence to make a recommendation one way or the other.
Two things make it difficult to assess the value of multivitamins.
On the one hand, there’s the “healthy user effect.” This describes the fact that people who take multivitamins tend to do a lot of beneficial things, including eating fruits and vegetables, regular exercise and abstaining from smoking. When assessing the relationship between multivitamin use and longevity, these habits could make the pills seem more beneficial than they actually are.
On the other hand, there’s the “sick user effect.” People who are diagnosed with a chronic disease often respond by adding a multivitamin to their daily regimen. In real-world studies, this links the supplements to poorer health and tends to make them seem less helpful than they truly are.
To help fill the gaps left by prior research, a team led by epidemiologist Erikka Loftfield collected data from three large studies that tracked participants over decades — the National Institutes of Health-AARP Diet and Health Study; the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial and the Agricultural Health Study. Anyone who had a chronic condition when they enrolled was excluded from the team’s analysis.
A total of 390,124 people across the three studies shared information about their multivitamin use, and half of them were at least 61½ years old when they began being tracked. By the time the study period came to an end — December 2019 or December 2020, depending on which cohort they were in — 164,762 of them had died, including roughly 50,000 deaths from cancer and 35,000 deaths from heart disease.
There were some clear differences between those who took multivitamins and those who didn’t. For example, 49 percent of the people who took a multivitamin every day were women, compared with 39 percent of those who never took them. In addition, 42 percent of those with a daily multivitamin habit had gone to college, compared with 38 percent of those who hadn’t.
The researchers calculated that the people who eschewed all multivitamins had the lowest risk of death during the first 12 years. Compared to them, the mortality rate was 4 percent higher for those who took multivitamins daily and 9 percent higher for those who took them less often.
