If you're taking a multivitamin to help you live longer, a new study by researchers at the National Cancer Institute may make you reconsider.
After analyzing health and nutrition data from nearly 400,000 Americans, researchers found that people who took multivitamins had a small but significantly higher risk of premature death than people who avoided supplements.
The findings, published Wednesday in the journal JAMA Network Open, may seem disconcerting. Americans aren't known for having the most balanced diets, and popping a pill to fill our nutritional gaps is often touted as a sensible insurance policy.
Also, vitamins are essential. It would be logical to think that the more you take, the better.
But like so many things related to our health, the science is not that simple.
As recently as 2022, experts from the U.S. Preventive Services Task Force conducted a comprehensive review of the medical literature on the potential of multivitamins to help prevent cardiovascular disease and cancer. They concluded that there was not enough reliable evidence to make a recommendation one way or the other.
Two things make it difficult to evaluate the value of multivitamins.
On the one hand, there is the “healthy user effect”. This describes the fact that people who take multivitamins tend to do many beneficial things, such as eating fruits and vegetables, exercising regularly, and abstaining from smoking. When evaluating the relationship between multivitamin use and longevity, these habits could make pills or liquids seem more beneficial than they really are.
On the other hand, there is the “sick user effect”. People diagnosed with a chronic illness often respond by adding a multivitamin to their daily regimen. In real-world studies, this links supplements to poorer health and tends to make them seem less useful than they really are.
To help fill in gaps left by previous research, a team led by epidemiologist Erikka Loftfield compiled data from three large studies that tracked participants for decades: the National Institutes of Health-AARP Diet and Health Study; the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO); and the Agricultural Health Study. Anyone who had a chronic disease when they enrolled was excluded from the team’s analysis.
A total of 390,124 people in the three studies shared information about their multivitamin use, and half of them were at least 61 1/2 years old when they began being tracked. By the time the study period ended (December 2019 or December 2020, depending on which cohort they were in), 164,762 of them had died, including about 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 did not. For example, 49% of people who took a multivitamin every day were women, compared to 39% of those who never took them. Additionally, 42 percent of those with a daily multivitamin habit had gone to college, compared to 38 percent of those who had not.
The health habits of vitamin consumers and non-consumers were also different. People who took multivitamins every day were less likely to smoke, more likely to exercise, had higher diet quality and lower body mass index scores, and were more likely to take vitamin and mineral supplements. individual.
After accounting for those and other differences, the researchers calculated that people who avoided multivitamins altogether had the lowest risk of death during the first 12 years they were followed. Compared with them, the death rate was 4% higher for those who took multivitamins daily and 9% higher for those who took them less frequently.
Younger vitamin users had the highest risk. Among those who joined one of the studies before turning 55, the mortality rate of those who took the supplements every day was 15% higher than those who did not take them at all.
Loftfield and his team also compared mortality risks over the next 15 years. Over that longer time horizon, there were no statistically significant differences between the three groups.
This may not be good news for the roughly 1 in 3 Americans who take a multivitamin at least once a month, and who do so even though researchers have been saying for years that vitamin supplements fall short. of its healthy reputation.
“Several vitamins overpromise and underdeliver,” said Dr. Neal D. Barnard, president of the Physicians Committee for Responsible Medicine. “They got this undeserved reputation for being an essential aspect of a healthy lifestyle.”
Barnard and two of his PCRM colleagues explained how this came about in a commentary accompanying the study.
The importance of individual nutrients began to become evident centuries ago, they wrote. For example, lime juice was found to cure scurvy in sailors long before anyone realized that the juice was a delivery vehicle for vitamin C. Similarly, doctors prevented beriberi by replacing white rice for brown rice before understanding that the polishing process removed the outer layer of the grain. layers, which are rich in thiamine.
Multivitamins separated from food became a commercial product in the 1940s, and Americans now spend $8 billion a year on supplements.
There are some cases in which vitamin pills may be helpful, Barnard and his colleagues wrote. People with age-related macular degeneration can slow the progression of the disease by taking a cocktail of beta-carotene, zinc, and vitamins C and E. Multivitamin use by older adults has been linked to improved memory and cognitive function. And people who have had bariatric surgery are recommended to take multivitamins to compensate for the fact that their bodies can no longer extract as many nutrients from food.
But those benefits don't extend to avoiding death. In fact, taking the pills can be counterproductive.
Multivitamins containing calcium and zinc can impede the body's ability to absorb antibiotics. Multivitamins with vitamin K can counteract the blood-thinning benefits of warfarin, a drug taken by millions of Americans to prevent dangerous blood clots. The iron contained in multivitamins can cause hemochromatosis, which puts patients at risk for cardiovascular disease, liver failure, and Alzheimer's, among other problems.
“There's a pretty big downside to all of this,” said Barnard, 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 vitamins to help you, you'll be much better off getting them directly from food, Loftfield said. Barnard agreed.
“Taking a vitamin completely out of its context and increasing the dosage to a formulation that nature never really saw is not necessarily a good idea,” he said. “Mortality decreases with dietary patterns, not with pills.”
