Authored by Cara Michelle Miller via The Epoch Times (emphasis ours),
Every morning, millions of people take a vitamin D supplement, thinking mostly about stronger bones and a healthier immune system. However, quietly, at the cellular level, something else may be happening—something that could change how we think about aging.
A long-running study recently found that people who took daily vitamin D supplements for four years had slightly less shortening of their telomeres—a marker linked to cellular aging—than those who didn’t.
While experts caution that the real-world health benefits remain unclear, the findings could shed light on the protective effects of vitamin D on specific aging-related diseases, the study authors noted.
A Small but Significant Finding
The study, known as the VITamin D and OmegA-3 TriaL (VITAL), showed that people taking 2,000 IUs of vitamin D lost about 140 fewer base pairs from their telomeres than those taking a placebo—a small but statistically significant difference.
Telomeres are regions of DNA at the ends of chromosomes that naturally shorten with age. Shorter telomeres have been linked to health risks like heart disease and Alzheimer’s disease.
The study findings suggest a promising role for vitamin D in slowing a pathway for biological aging and age-related chronic disease, Dr. JoAnn Manson, the study’s coauthor and a professor of medicine at Harvard Medical School, said in an email to The Epoch Times.
Although the results are encouraging, Manson says more research is needed. “Replication of these results in another randomized trial will be important before changing general guidelines for vitamin D intake.”
The Reality Check
Participants in the study started out with an average of 8,700 base pairs. Independent experts say the difference in loss of base pairs observed in the study is very small and falls within the range of normal fluctuation, meaning it may not translate into measurable real-world benefits.
“This 140-base-pair difference is like saying your hemoglobin went from 13.0 to 13.1,” said Dr. Mary Armanios, a professor of oncology and director of the Telomere Center at Johns Hopkins University. “It trends in the right direction, but it doesn’t carry clinical meaning.”
“It is only at the extremes that telomere length matters in aging,” she added.
More broadly, Armanios cautioned against thinking of telomeres as a simple aging clock. While very short telomeres can signal aging-related disease, unusually long ones are not always better and have been linked to higher cancer risk, according to 2023 research from her group published in the New England Journal of Medicine.
“Most people fall in a healthy middle range, and that’s exactly where we want to be,” she said.
She also noted that the method used to measure telomere length—quantitative polymerase chain reaction (qPCR)—can be affected by lab factors like temperature and sample handling. These variables can make small differences unreliable. Among telomere testing methods, qPCR is the least reproducible.
A Closer Look at Vitamin D Supplementation
While some experts urge caution in interpreting the telomere data, Manson said the new findings align with earlier VITAL results. Those results showed that vitamin D reduced inflammatory markers and lowered the risk of advanced cancers and autoimmune diseases by improving immune function.
Previous studies on vitamin D and telomere length have shown mixed results, including some that found no effect—or even a correlation between higher vitamin D levels and shorter telomeres.
Guidelines from the National Academy of Medicine recommend 600 IU per day for most adults and 800 IU for those over 70. The Endocrine Society also recommends supplements for older adults, people with prediabetes, and others at higher risk of deficiency.
“Most professional societies do not recommend routine vitamin D screening or supplementation for the general population,” said Manson.
However, certain groups—older adults, those with limited sun exposure or absorption issues such as Crohn’s disease or celiac disease—may benefit from modest supplementation.
Other studies have suggested that vitamin D may promote healthy aging in older people.
The DO-HEALTH trial, a large European study in adults age 70 and older, found that daily 2,000 IU of vitamin D led to modest improvements in bone strength and infection rates—but not a reduction in new chronic diseases.
Longer-term observational research, like Germany’s ESTHER study, linked higher vitamin D levels with lower rates of cardiovascular disease and all-cause mortality. However, as a nonrandomized study, it couldn’t rule out confounding lifestyle factors.
More large, diverse, and long-term trials are needed to determine who benefits most, at what dose, and for which outcomes.
Vitamin D metabolism is tightly regulated by the body, so only small to moderate amounts are needed to support health. A 2,000 IU daily dose is safe, as demonstrated in the five-year VITAL trial, with no increased risk of side effects.
Very large doses—over 10,000 IU per day—may lead to elevated calcium levels and potential toxicity, Manson noted.
What This Means for You
For now, experts agree that this latest analysis does not mean everyone should start taking vitamin D supplements to slow aging.
“Vitamin D has known benefits, like for bone health,” Armanios said, “but telomere length shouldn’t be the main reason to start taking supplements.”
However, for those already taking vitamin D for bone, muscle, or immune support, the findings may offer one more reason to continue.
Vitamin D is found in fortified foods such as milk, cereal, and orange juice, and in fatty fish like salmon and sardines. Moderate sun exposure also helps the body make its own supply.
“Although it’s easier to pop a pill,” said Armanios, “being active outdoors and eating a healthy diet will do far more to support long-term health.”
Marion Nestle, a professor emerita of nutrition and public health at New York University, said the findings are intriguing but still require further confirmation and clarity on their clinical significance.
In the meantime, she encouraged people to spend time outdoors when possible, noting that “sunlight on skin is the best source of vitamin D, far superior to supplements—even if just for a few minutes a day.”
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