A new study published in The American Journal of Clinical Nutrition suggests that vitamin D supplementation may slow biological aging by preserving the length of telomeres—the protective caps at the ends of chromosomes. These structures naturally shorten with age, and their deterioration is linked to chronic conditions such as type 2 diabetes and cardiovascular disease.
The findings come from the VITAL Telomere Study, a sub-study of the larger VITAL trial—a long-term, randomized, double-blind, placebo-controlled study involving nearly 26,000 U.S. adults (women aged 55+ and men aged 50+). In the telomere-focused sub-study, 1,054 participants were monitored over four years, with telomere length in their white blood cells measured at baseline, two years, and four years.
Participants who received 2,000 International Units (IU) of vitamin D3 daily experienced significantly less telomere shortening than those who received a placebo. After four years, telomere length declined by just 7% in the vitamin D group, compared to a 28% decrease in the placebo group—a difference equivalent to nearly three years of biological aging.
“VITAL is the first large-scale, long-term randomized trial to show that vitamin D supplements can preserve telomere length,” said Dr. JoAnn Manson, the trial’s principal investigator and professor at Harvard Medical School, as quoted by The Independent. “This is particularly noteworthy, as previous results from VITAL also showed vitamin D’s potential to reduce inflammation and lower risks of some chronic diseases of aging, including advanced cancer and autoimmune disorders.”
Participants were randomly assigned to receive vitamin D3, omega-3 fatty acids (1g/day), both, or a placebo. While vitamin D demonstrated a protective effect on telomere length, omega-3 supplements did not show any measurable benefit in this regard.
“Targeted vitamin D supplementation may be a promising strategy to slow a biological aging process,” said lead author Haidong Zhu, a molecular geneticist at the Medical College of Georgia, Augusta University, in a Newsweek interview. “Still, further research is needed.”
Telomeres consist of repetitive DNA sequences that prevent chromosomes from fraying or fusing with others. As cells divide, telomeres gradually shorten, eventually reaching a point where the cell can no longer divide and becomes inactive or dies—a process associated with aging and disease.
However, some experts urge caution in interpreting the findings. “Telomere length really only becomes critical at the extremes,” noted Dr. Mary Armanios, director of the Telomere Center at Johns Hopkins University, in a Scientific American interview. “Most people have telomere lengths within a normal range, with significant buffering capacity.”
While vitamin D shows potential as a tool to delay biological aging, experts emphasize it should not replace a healthy lifestyle. “Supplements are no substitute for a balanced diet and healthy habits,” said Manson in The Washington Post. “But for individuals with higher inflammation levels or elevated chronic disease risk, targeted supplementation may offer benefits.”
Often called "the sunshine vitamin," vitamin D plays a key role in immune function, calcium absorption, bone health, and inflammation regulation. While sun exposure remains the most natural way to produce vitamin D, factors like geography, skin pigmentation, sunscreen use, and lifestyle can limit its effectiveness, making supplementation useful for many individuals.