When we imagine aging, we often think of the outward signs, such as graying hair or wrinkles. But aging also occurs where we can’t see it—in our organs, tissues, cells, and even in our DNA—and those changes affect more than how we feel when we look in the mirror. If our chromosomes suffer more age-related wear and tear, we can reasonably expect to feel older faster—but there may be a way to counteract that, reports a new study.
Published in the peer-viewed American Journal of Clinical Nutrition, the July 2025 study, known as the VITAL Telomere Study, found that taking a widely popular vitamin—vitamin D—could help slow aging by supporting healthy DNA. The key, according to researchers from Harvard, the Brigham and Women’s Hospital, the Medical College of Georgia, and University of Massachusetts Lowell, is the maintenance of a little-known feature of cellular biology: telomeres.
Telomeres are the protective caps at the ends of chromosomes which keep those DNA strands from fraying or tangling, explains the National Institutes of Health (NIH). You can think of them like the plastic ends of shoelaces, there to prevent deterioration. “Each time a cell divides, the telomeres become slightly shorter. Eventually, they become so short that the cell can no longer divide successfully, and the cell dies,” NIH experts write.
Shortening telomeres are a normal part of aging, but the study says the process is also linked to diseases such as cancer and heart disease. Because of this, scientists are interested in finding ways to slow down telomere shortening.
The VITAL Telomere Study looked at whether taking vitamin D3 or omega-3 fatty acids could help protect telomeres over time. The study was part of a larger clinical trial involving over 25,000 U.S. adults aged 50 and older. A smaller group of 1,054 participants had their telomere lengths measured at the beginning of the study, after two years, and again after four years. Participants were randomly given either:
After four years, the researchers found that people who took vitamin D3 (2,000 individual units or 50 micrograms per day) had slower telomere shortening compared to those who took the placebo. The dosage used in the study was notably higher than the NIH daily recommended intake for vitamin D, which is 600 to 800 IU (individual units) or 20 micrograms (mcg) for adults and children over the age of four.
Says an NIH recap of the study: “When researchers compared telomere length in white blood cells between the two groups, they found a significant difference.” Mainly, the subjects taking vitamin D3 lost about 140 fewer base pairs of telomere DNA over the course of four years (you can think of these as the paired rungs on the ladder-like structure of a DNA molecule)—suggesting that the vitamin might help protect chromosomes from aging. Based on previous studies, “that could equal up to three years of aging.” However, omega-3 supplements, administered in single-gram daily doses, did not show any effect on telomere length in this study.
But there was other standout findings in the study, too. When compared with placebo, a daily vitamin D3 supplementation “reduced the incidence of advanced (metastatic or fatal) cancer by 17%.” Continues the study: “Moreover, supplementation with vitamin D”—with or without omega 3s over the span of five years—”reduced all incident autoimmune diseases by 22%.”
Before taking any new supplement, including vitamin D, be sure to speak with your doctor or pharmacist first.
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