A clinical trial suggests vitamin D may slow cellular aging by preserving telomeres. Researchers urge caution on dosing and emphasize lifestyle as the most reliable path to healthy aging.
Vitamin D supplements may help safeguard the protective caps on our chromosomes that influence the pace of aging, raising hopes that the “sunshine vitamin” could support healthier longevity, according to a recent study.
Researchers reported that taking 2,000 IU (international units, a standard vitamin measurement) of vitamin D each day helped preserve telomeres, the small structures at the ends of chromosomes that act like the plastic tips of shoelaces, shielding DNA from damage during cell division.
Each of our 46 chromosomes ends with a telomere, which gradually shortens every time a cell divides. Once telomeres become critically short, cells lose the ability to divide and ultimately die.
Shortened telomeres have been associated with several major age-related conditions, including cancer, heart disease, and osteoarthritis. Factors such as smoking, chronic stress, and depression appear to accelerate this process, while inflammatory processes in the body also contribute to telomere loss.
Beyond strong bones
Vitamin D is widely recognized for its role in bone health, particularly in helping the body absorb calcium. Adequate intake is especially important for children, adolescents, and individuals with darker skin or limited sun exposure to ensure proper bone growth and maintenance.
But vitamin D also powers our immune system. A review of evidence found that vitamin D supplements can cut respiratory infections, especially in people who are deficient.
Early research even suggests it might help prevent autoimmune diseases like rheumatoid arthritis, lupus and multiple sclerosis, though more trials are needed.
Since inflammation damages telomeres, vitamin D’s anti-inflammatory effects could explain its protective role.
Testing vitamin D in a clinical study
In this recent study, from Augusta University in the US, the researchers followed 1,031 people with an average age of 65 for five years, measuring their telomeres at the start, after two years, and after four years. Half took 2,000 IU of vitamin D daily, while the other half received a placebo.
The results showed that telomeres were preserved by 140 base pairs in the vitamin D group, compared with a placebo. To put this in context, previous research found that telomeres naturally shorten by about 460 base pairs over a decade, suggesting vitamin D’s protective effect could be genuinely meaningful.
This isn’t the first promising finding. Earlier studies have reported similar benefits, while the Mediterranean diet – rich in anti-inflammatory nutrients – has also been linked to longer telomeres.
The catch
But there are some important points to note. Some researchers warn that extremely long telomeres might actually increase disease risk, suggesting there’s a sweet spot we don’t yet understand.
There’s also no agreement on the right dose. The Augusta researchers used 2,000 IU daily – much higher than the current recommended intake of 600 IU for under-70s and 800 IU for older adults. Yet other research suggests just 400 IU might help prevent colds.
Experts say the optimal dose probably depends on individual factors, including existing vitamin D levels, overall nutrition, and how the vitamin interacts with other nutrients.
Although these findings are exciting, it’s too early to start popping high-dose vitamin D in the hope of slowing aging. The strongest evidence for healthy aging still points to the basics: a balanced diet, regular exercise, quality sleep, not smoking, and managing stress, all of which naturally support telomere health.
However, if you’re deficient in vitamin D or at risk of poor bone health, supplements remain a sensible choice backed by decades of research. As scientists continue unravelling the mysteries of aging, vitamin D’s role in keeping our cellular clocks ticking may prove to be just one piece of a much larger puzzle.
Reference: “Vitamin D3 and marine ω-3 fatty acids supplementation and leukocyte telomere length: 4-year findings from the VITamin D and OmegA-3 TriaL (VITAL) randomized controlled trial” by Haidong Zhu, JoAnn E Manson, Nancy R Cook, Bayu B Bekele, Li Chen, Kevin J Kane, Ying Huang, Wenjun Li, William Christen, I-Min Lee and Yanbin Dong, 21 May 2025, The American Journal of Clinical Nutrition.
DOI: 10.1016/j.ajcnut.2025.05.003
Adapted from an article originally published in The Conversation.
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