If you’re taking a multivitamin to help you live longer, a new study from 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 results, reported Wednesday in the journal JAMA Network Open, may seem puzzling. Americans aren’t known for eating the most balanced diets, and popping a pill to make up for our nutritional deficiencies is often touted as a wise insurance policy.
Additionally, vitamins are essential. It stands to reason that the more you take, the better.
But as with many things regarding 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 regarding 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 assess 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, including eating fruits and vegetables, exercising regularly, and refraining from smoking. When evaluating the relationship between multivitamin use and longevity, these habits could make pills or liquids appear more beneficial than they actually are.
On the other hand, there is a “sick-drinking effect.” People with chronic illness often respond by adding a multivitamin to their daily regimen. In real-world studies, this associates supplements with poor health and tends to make them seem less helpful than they actually are.
To help fill in the gaps left by previous research, a team led by epidemiologist Erikka Loftfield collected data from three large studies that followed participants over decades: the National Diet and Health Study Institutes of Health-AARP; the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial and the Agricultural Health Study. Anyone with a chronic illness at the time of enrollment was excluded from the team’s analysis.
A total of 390,124 people in the three studies shared information about their multivitamin intake, and half of them were at least 61½ years old when they began being followed. By the end of the study period – 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 clear differences between those who took multivitamins and those who did not. For example, 49% of people who took daily multivitamins were women, compared to 39% of those who never took them. Additionally, 42% of those who took daily multivitamins had gone to college, compared to 38% of those who had not.
The health habits of vitamin users and non-users were also different. People who took daily multivitamins were less likely to smoke, more likely to exercise, had higher diet quality scores and lower body mass index scores, and were more likely to take individual vitamin and mineral supplements.
After accounting for these and other differences, the researchers calculated that people who avoided all multivitamins had the lowest risk of death during the first 12 years of their follow-up. Compared to them, the mortality rate was 4% higher for those who took multivitamins daily and 9% higher for those who took them less often.
Younger vitamin users had the highest risk. Among those who joined one of the studies before their 55th birthday, the mortality rate of those who took supplements daily was 15% higher than that of those who did not take them at all.
Loftfield and his team also compared mortality risks over the following 15 years. Over this longer time horizon, there were no statistically significant differences between the three groups.
That may not be good news for the roughly one in three Americans who take a multivitamin at least once a month — and who does so despite the fact that researchers have said for years that vitamin supplements are not safe. live up to their reputation for good health.
“Several vitamins overpromise and underdeliver,” said Dr. Neal D. Barnard, chairman of the Physicians Committee for Responsible Medicine. “They have gained this undeserved reputation for being an essential aspect of a healthy lifestyle. »
Barnard and two of his PCRM colleagues explained how this happened in a commentary that accompanies the study.
The importance of individual nutrients began to become apparent centuries ago, they write. For example, lime juice was found to cure sailors of scurvy long before anyone realized that lime juice was a carrier of vitamin C. Likewise, doctors prevented beriberi by replacing white rice with brown rice. before realizing that the polishing process removed the outer layer of grain. layers 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 where vitamin pills can be helpful, Barnard and 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. Use of multivitamins by older adults has been linked to increased better memory and cognitive function. And people who have had bariatric surgery are advised to take multivitamins to compensate for the fact that their body is no longer able to extract as many nutrients from food.
But these benefits do not extend to the prevention of death. Indeed, taking these pills can have counterproductive effects.
Multivitamins containing calcium and zinc may interfere with the body’s ability to absorb antibiotics. Multivitamins containing vitamin K may counteract the blood-thinning effects of warfarin, a medication taken by millions of Americans to prevent dangerous blood clots. The iron in multivitamins can lead to hemochromatosis, which puts patients at risk for cardiovascular disease, liver failure, and Alzheimer’s disease, among other problems.
“All of this has a major downside,” said Barnard, who is also an assistant professor at George Washington University School of Medicine and Health Sciences. “These illnesses are not just benign. »
In most cases, if you want vitamins to help you, it would be best to get them directly from food, Loftfield said. Barnard agreed.
“Taking a vitamin completely out of context and increasing the dosage to a formulation that nature never really saw is not necessarily a good idea,” he said. “Mortality is reduced by eating habits, not by pills. »