If you’ve ever taken a vitamin D supplement, your goal was probably to improve bone health or ward off seasonal affective disorder. But research published in The American Journal of Clinical Nutrition points to another potential benefit: delaying biological aging.
The study used data from about 1,000 adults ages 50 and up who took vitamin D3 supplements, omega-3 fatty acid supplements, both, or neither every day for five years. The participants gave blood samples at multiple points over a four-year period, and using those blood samples, researchers measured a key marker of cellular aging: the length of participants’ telomeres.
Telomeres serve as protective caps at the ends of chromosomes, similar to the bits of plastic at the ends of shoelaces. They shorten over time, and when they get very short, they trigger biological processes that stop cell division and contribute to aging-related disease, explained Sandy Chang, MD, PhD, a professor of laboratory medicine at the Yale School of Medicine who was not involved in the new research but studies telomeres.
Finding ways to elongate telomeres, then, could theoretically slow the aging process.
The study suggests vitamin D supplementation may help with that. People who took 2,000 international units (IUs) of vitamin D3 per day lost less of their telomeres over time than people who took a placebo, the researchers found.
“It was like preventing three years of aging during that four-year period,” said study co-author JoAnn Manson, MD, MPH, DrPH, chief of preventive medicine at Brigham and Women’s Hospital in Boston.
But Chang said there are a few reasons to view that conclusion with a little skepticism. For one thing, the study only analyzed telomeres within white blood cells, so it’s impossible to say what happens in other types of cells. And even within white blood cells, vitamin D’s effect on telomeres appeared “modest,” Chang told Health.
Perhaps most importantly, the study didn’t assess what that effect actually means for human aging. “They haven’t done the functional study,” Chang said. “Are these cells really benefitting from this slight elongation in telomeres?”
People do need vitamin D. Recommendations generally say that adults should get 600 to 800 IUs per day, as the nutrient supports bone, muscular, and immune health, among other functions.
But if you’re after anti-aging, save your money, said David Seres, MD, ScM, a professor of medicine in the Institute of Human Nutrition at Columbia University Irving Medical Center in New York City who was not involved in the new research.
The relationship between vitamin D and telomeres is “a starting place for possible future research,” Seres told Health, but it shouldn’t prompt anyone to start taking capsules. To prove that people benefit, further studies would need to assess whether supplementation is linked to actual health benefits—not just longer telomeres. “The road is littered with studies of these kinds of associations failing,” Seres said, so it’s best to wait for the data.
Manson agreed. She hopes her group’s study will “stimulate more research,” but said it’s premature to alter guidelines based on its findings.
Most people can get enough vitamin D by spending time in the sun and eating foods such as fish and fortified dairy. But should you also take a supplement?
That’s controversial in the medical field. Some experts—like Seres—say supplementation is rarely necessary, while others think it’s appropriate for people at increased risk of vitamin D deficiency, such as older adults and people with certain digestive conditions.
However, the United States Preventive Services Task Force (USPSTF), an expert body that makes evidence-based health recommendations, says there is insufficient data to determine whether healthy adults should get screened for vitamin D deficiency.
Even among people in higher-risk groups, the data on vitamin D aren’t entirely clear. In 2024, for example, the USPSTF published a draft recommendation urging older adults not to take vitamin D to prevent falls and bone fractures.
Previous studies using VITAL trial data also paint a murky picture. VITAL was originally designed to assess whether supplements reduced the risk of developing cancer or cardiovascular disease among adults 50 and older; they did neither. Other analyses of the data, however, suggest that vitamin D supplements may improve cancer survival and decrease inflammation.
Even if the benefits of vitamin D aren’t totally proven, is there harm in taking a supplement to hedge your bets?
“I would not think of supplementation as harmless,” Seres said. While current data suggest vitamin D supplements are safe, health authorities do not recommend taking more than 4,000 IUs per day. At very high doses, vitamin D can cause side effects ranging from nausea and muscle weakness to kidney failure and irregular heartbeat.
In short, plan A should be getting the vitamin D you need without popping a pill. “Vitamin D supplements and other dietary supplements will never be a substitute for a healthy diet and a healthy lifestyle,” Manson told Health. “That is still worth emphasizing.”
