Vitamin D May Slow Cells' Aging by Protecting DNA

Yahoo

22-05-2025

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.'
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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.
'Vitamin D supplementation is able to slow down the telomere shortening process, at least during the four-year period,' says the study's first author Haidong Zhu, a molecular geneticist at the Medical College of Georgia at Augusta University.
Participants started out with an average of 8,700 base pairs of DNA telomere length, and vitamin D supplementation slowed the loss of length by about 140 base pairs over four years, the study found.
The health implications of that number aren't clear. 'It's only at the extremes that telomere length really matters in terms of aging,' cautions Mary Armanios, a professor of oncology and director of the Telomere Center at Johns Hopkins University, who was not involved in the research. The magnitude of difference seen in the vitamin D trial is within the normal range of human variation, meaning it may not equate with aging or youthfulness in any clinical sense.
'Most of us are going to be within this normal range, and there is a wide buffer for how much telomere length can change,' Armanios says.
In addition, Armanios says, the study used a method called quantitative polymerase chain reaction (qPCR) to assess telomere length, and this method can be very sensitive to factors such as when samples were collected and what time elapsed between collection and testing. 'The methodology for telomere length measurement has been compared to others and found to be the least reproducible,' she says.
A large study of people aged 60 and older in the U.K. also found that very high levels of vitamin D in the blood were associate with shorter telomeres, suggesting that more is not always better. The participants in the VITAL study were supplemented with a moderate amount of vitamin D, Manson says.
Most of the participants in the new study were white, Zhu adds, so the results need to be replicated in a more diverse sample. The researchers are also currently analyzing data from the 1,054 VITAL participants to understand other facets of cellular aging, including DNA methylation, a type of regulation of gene expression.
The results are intriguing, says Anastassios Pittas, a professor of medicine at the Tufts University School of Medicine, who was not involved in the study. Vitamin D supplements are now recommended by the Endocrine Society for people aged 75 and older, as well as for people of any age with prediabetes to prevent the onset of type 2 diabetes, Pittas says. 'These new findings from the VITAL study lend scientific support to these recommendations, highlighting possible mechanisms through which vitamin D may influence long-term health outcomes,' he says.
The findings are leading researchers toward a better understanding of who should pop a daily supplement, Manson says. 'It shouldn't be a universal recommendation to be screened for vitamin D blood levels or to take a supplement,' she says. 'But it appears that selected high-risk groups may benefit.'