You can take vitamin D supplements to support bone health or ease seasonal affective disorder. But a 2025 study published in The American Journal of Clinical Nutrition highlights another potential benefit: delaying biological aging.
The study used data from about 1,000 adults ages 50 and older who took vitamin D3 supplements, omega-3 fatty acid supplements, both, or neither every day for five years. Participants gave blood samples multiple times over a four-year period. Using these blood samples, the researchers measured a key marker of cellular aging: the length of the participants’ telomeres.
Telomeres serve as protective caps on the ends of chromosomes, similar to the pieces of plastic on the ends of shoelaces. They shorten over time, and when they become very short, they trigger biological processes that stop cell division and contribute to aging-related diseases, explained telomere researcher Sandy Chang, MD, PhD, professor of laboratory medicine at the Yale School of Medicine, who was not involved in the study.
Finding ways to lengthen telomeres could therefore theoretically slow the aging process.
The study suggests that vitamin D supplementation could help. People who took 2,000 international units (IU) of vitamin D3 per day lost fewer of their telomeres over time than people who took a placebo, the researchers found.
“It was like preventing three years of aging in 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 several reasons to view this conclusion with some skepticism. For one thing, the study only analyzed the telomeres of white blood cells, so it’s impossible to say what’s happening in other cell types. And even in white blood cells, vitamin D’s effect on telomeres seemed “modest,” Chang told HEALTH.
Perhaps more importantly, the study did not assess what this effect actually means about human aging. “They didn’t do a functional study,” Chang said. “Do these cells really benefit from this slight lengthening of telomeres?
People need vitamin D. Recommendations generally state that adults should get between 600 and 800 IU per day, as this nutrient supports bone, muscle, and immune health, among other functions.
But if you’re looking for an anti-aging treatment, save your money, said David Seres, MD, ScM, professor of medicine at the Institute of Human Nutrition at Columbia University Irving Medical Center, who was not involved in the research.
The relationship between vitamin D and telomeres is “a starting point for possible future research,” Seres told HEALTH, but it shouldn’t inspire anyone to start taking capsules.
To prove that people benefit, further studies should assess whether supplementation is linked to real health benefits, not just longer telomeres. “The path is littered with studies of these kinds of associations that fail,” Seres said, so it’s best to wait for more data.
Manson agreed. She hopes her group’s study will “stimulate more research” but believes it is premature to change the guidelines based on its findings.
Most people can get enough vitamin D by spending time in the sun and eating foods like fish and fortified dairy products. But should you also take a supplement?
This is controversial in the medical field. Some experts, like Seres, say supplementation is rarely necessary, while others believe it is appropriate for people at increased risk of vitamin D deficiency, such as older adults and people with certain digestive problems.
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 be tested for vitamin D deficiency.
Even among people in higher risk groups, the data on vitamin D is not entirely clear. In 2024, for example, the USPSTF issued a draft recommendation urging older adults not to take vitamin D to prevent falls and bone fractures.
Previous studies using data from the VITAL trial also paint a murky picture. VITAL was initially designed to evaluate whether supplements reduced the risk of developing cancer or cardiovascular disease in adults aged 50 and older; they did neither. Other analyzes of the data, however, suggest that vitamin D supplements may improve cancer survival and decrease inflammation.
Even though the benefits of vitamin D aren’t fully proven, is there any downside to taking a supplement to hedge your bets?
“I wouldn’t consider supplementation harmless,” Seres said. Although current data suggests that vitamin D supplements are safe, health authorities do not recommend taking more than 4,000 IU 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 about getting the vitamin D you need without taking a pill. “Vitamin D supplements and other dietary supplements will never replace a healthy diet and lifestyle,” Manson told HEALTH. “This is still worth emphasizing.”
Gn Health
