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Vitamin D May Slow Cells’ Aging by Protecting DNA
Vitamin D supplements may help prevent the loss of telomeres, DNA sequences that shrink with aging, a large study shows. But the health effects aren’t yet clear
May 21, 2025
4 min read
Vitamin D May Slow Cells’ Aging
Vitamin D supplements may help prevent the loss of telomeres, DNA sequences that shrink with aging, a large study shows. But the health effects aren’t yet clearBy Stephanie Pappas edited by Jeanna Bryner
A new study suggests vitamin D supplements might slow cellular aging by protecting telomeres.
Olga Pankova/Getty Images
Aging
Vitamin D supplements might slow cellular aging by preventing the loss of telomeres, DNA sequences at the ends of chromosomes that shorten in old age, a new study suggests. The health effects of these findings aren’t yet clear.
Vitamin D had been touted as a panacea for a number of health conditions, from cardiovascular disease to bone loss. In 2020 a large randomized controlled trial of supplementation instead found benefits only in a few conditions, particularly autoimmune disease and advanced cases of cancer, says the new study’s co-author JoAnn Manson, a professor of medicine at Harvard Medical School and a principal investigator of that large trial, called the VITamin D and OmegA-3 TriaL (VITAL). The new study is an analysis of data from VITAL. Its finding could explain the protective effect of vitamin D supplements on these specific aging-related diseases, Manson says.
“If is replicated in another randomized trial of vitamin D supplements, I think this could translate into clinical effects for chronic diseases of aging,” she says. “We’re already seeing that vitamin D does reduce inflammation; it reduces advanced cancers and cancer deaths, as well as autoimmune diseases. This could provide a biological mechanism.”
In the VITAL project, researchers enrolled nearly 26,000 women aged 55 or older and men aged 50 or older, and they randomly assigned participants to take vitamin D supplements, fish oil supplements, a combination of both or a placebo. For the new study, published today in the American Journal of Clinical Nutrition, the scientists looked at a subset of 1,054 participants who lived close enough to Harvard’s Clinical and Translational Science Center in Boston to have their blood drawn three times over four years so researchers could measure their telomeres.
Inside the nuclei of most cells in the human body reside 46 chromosomes, where our DNA is neatly packed. Each time a cell divides, these chromosomes unravel and copy themselves, and the copies coil back into the nuclei of the new cells. Telomeres are repetitive DNA sequences that cap the ends of chromosomes. They stabilize the chromosomes during cell division, though they get shorter each time cells divide. When the telomeres get very short, the cells stop dividing and die. Over time, as more and more of our cells die, the body ages and ultimately stops functioning. Telomeres aren’t a perfect clock for health—very long telomeres can increase cancer risk by stabilizing mutated cells—but they’re often used as a biomarker for aging.
Participants in the placebo and supplement groups had similar telomere lengths at the beginning of the study, the researchers found. But over the four years of follow-up, people assigned to take 2,000 international units of vitamin D per day showed less shortening of their telomeres compared with people in the placebo group. Fish oil had no significant effect.
