If you’re taking a multivitamin to extend your life, a new study from researchers at the National Cancer Institute may make you think twice.
Analyzing health and nutrition data from nearly 400,000 Americans, researchers found that people who took multivitamins had a slightly but significantly higher risk of early death than those who didn’t take supplements.
The findings, published Wednesday in JAMA Network Open, may seem puzzling: Americans aren’t known for eating the most balanced diets, and popping a pill to fill in nutritional gaps is often touted as a sensible insurance policy.
Plus, vitamins are essential, so it stands to reason that the more you get, the better.
But as with many things concerning our health, the science is not that simple.
As recently as 2022, experts from the U.S. Preventive Services Task Force conducted an extensive review of the medical literature on whether multivitamins may help prevent cardiovascular disease and cancer. They concluded that there was insufficient reliable evidence to recommend one over the other.
Evaluating the value of a multivitamin can be difficult for two reasons.
On the one hand, there’s the “healthy user effect,” which describes the fact that people who take multivitamins tend to do a lot of beneficial things, like eat fruits and vegetables, exercise regularly, and refrain from smoking. When assessing the relationship between multivitamin use and longevity, these habits can make a pill or liquid seem more beneficial than it actually is.
On the other hand, there’s also the “sick user effect.” People who are diagnosed with a chronic illness often respond by adding a multivitamin to their daily diet. In actual studies, this tends to link supplements to poorer health, making them seem less helpful than they actually are.
To fill in the gaps left by previous research, a team led by epidemiologist Ericka Loftfield pooled data from three large studies that followed participants over decades: the National Institutes of Health/AARP Diet and Health Study, the Prostate, Lung, Colon, and Ovarian (PLCO) Cancer Screening Trial, and the Agricultural Health Study. People who had chronic diseases at the time of participation were excluded from the team’s analysis.
A total of 390,124 people shared information about their multivitamin use across the three studies, half of whom were at least 61 1/2 years old when follow-up began. By the end of the study period (December 2019 or December 2020, depending on which cohort they were in), 164,762 people had died, including nearly 50,000 from cancer and 35,000 from heart disease.
There were some clear differences between those who took multivitamins and those who didn’t. For example, 49% of those who took daily multivitamins were women, compared to 39% of those who had never taken them. Additionally, 42% of those who took daily multivitamins were attending college, compared to 38% of those who didn’t.
Vitamin takers and non-takers also had different health habits: People who took daily multivitamins were less likely to smoke, more likely to be physically active, had higher diet quality scores, lower BMI scores, and were more likely to take separate vitamin and mineral supplements.
After taking these and other differences into account, the researchers calculated that during the first 12 years of follow-up, people who never took a multivitamin had the lowest risk of death, compared with a 4% higher risk of death among those who took a daily multivitamin and a 9% higher risk among those who took it infrequently.
Younger vitamin takers were at highest risk: Among people who joined the study before their 55th birthday, those who took daily supplements were 15% more likely to die than those who didn’t take them at all.
Loftfield and her team also compared the risk of death over the next 15 years, and found no statistically significant differences between the three groups over that long period.
That may not be welcome news to the roughly one in three Americans who take a multivitamin at least once a month, even though researchers have long said vitamins don’t live up to their reputation for health benefits.
“Multivitamins overpromise and underdeliver,” said Dr. Neal D. Barnard, president of the Physicians Committee for Responsible Medicine. “Multivitamins have earned an undeserved reputation as an essential component of a healthy lifestyle.”
In a commentary accompanying the study, Bernard and two of his PCRM colleagues explained how this result came about.
The importance of individual nutrients began to become apparent centuries ago, the researchers write. For example, lime juice was found to cure sailors with scurvy long before anyone realized that the juice was a vehicle for vitamin C. Similarly, doctors prevented beriberi by substituting brown rice for white rice before they realized that the milling process removes the thiamin-rich outer layer of rice.
Detached from food, multivitamins were commercialized in the 1940s, and Americans now spend $8 billion a year on supplements.
Bernard and his colleagues write that vitamin supplements may help in some cases. People with age-related macular degeneration may be able to slow the progression of the disease by taking a cocktail of beta-carotene, zinc, and vitamins C and E. Older people who take multivitamins have been shown to improve memory and cognitive function, and people who have had bariatric surgery are advised to take multivitamins to compensate for their bodies no longer being able to extract as many nutrients from food.
But those benefits don’t extend to delaying death — in fact, taking the drugs may actually have the opposite effect.
Multivitamins that contain calcium and zinc may inhibit the body’s ability to absorb antibiotics. Multivitamins that contain vitamin K may counteract the blood-thinning effects of warfarin, which millions of Americans take to prevent dangerous blood clots. Iron in multivitamins can cause hemochromatosis, putting patients at risk for cardiovascular disease, liver failure and Alzheimer’s disease.
“There are some pretty big drawbacks to all of this,” said Bernard, who is also an adjunct professor at George Washington University School of Medicine and Health Sciences. “They’re not just benign.”
In most cases, if you want to get vitamins, you’re much better off getting them directly from food, Loftfield said, and Bernard agreed.
“It’s not necessarily a good idea to completely remove vitamins from their intended use and increase the doses to combinations never found in nature,” he said. “Mortality is reduced by dietary patterns, not by drugs.”
