Vitamin D May Slow a Process Related to Aging, New Study Suggests

Yomiuri Shimbun

25-05-2025

People who have a higher vitamin D intake may be slowing down a biological process linked to aging, according to a study published this week.
But don't rush out to buy supplements just yet. The findings need to be confirmed with additional research, and the vast majority of people in the United States are already getting enough vitamin D from diet and sunlight, experts say.
In the new analysis, researchers at Brigham and Women's Hospital, Harvard Medical School, and other universities looked at telomeres – the protective caps of DNA code at the ends of chromosomes – which tend to shorten as we age.
It's a biological 'clock' of sorts, and shorter telomeres have been linked to an increased risk of certain diseases. Vitamin D supplements, though, may slow that shrinking process, the new research, published in the American Journal of Clinical Nutrition, has found.
While previous studies have shown an association between vitamin D and telomere length, most were observational. The new study is randomized, double-blind and placebo-controlled, lending more credence to the findings.
'We think these findings are promising and warrant further study. But we think that the replication will be important before changing the general guidelines for vitamin D intake,' said JoAnn Manson, a co-author of the study and chief of the Division of Preventive Medicine at Brigham and Women's Hospital in Boston.
Reduced telomere shortening
The findings are part of a larger study, called the VITAL trial, that Manson and other researchers from Brigham and Women's Hospital, an affiliate of Harvard Medical School, have been conducting for five years. It involves 25,871 participants – U.S. women age 55 and older and men age 50 and older – who have been given 2,000 IUs of vitamin D3 a day and 1 gram of Omega 3 fatty acid a day to determine their effects primarily on cancer and cardiovascular disease prevention.
The telomere study focused on about 900 of those participants, largely from Boston, whose telomere length in white blood cells was assessed at baseline and again in years 2 and 4.
Researchers found that compared with the group taking the placebo, those taking vitamin D supplements had reduced telomere shortening over four years. Omega 3 fatty acid supplementation, on the other hand, had no obvious effect on telomere length.
How telomeres may be associated with aging
During each cell division, telomeres ensure that the cell's chromosomes do not fuse with one another or rearrange themselves, and with each replication, the telomeres shorten a bit. This process is associated with aging as well as an increased risk of infections, type 2 diabetes and cardiovascular diseases.
The researchers think that vitamin D supplementation's benefit is related to tamping down inflammation, Manson said. Inflammation has been associated with autoimmune diseases as well as cancer.
Healthy diet and lifestyle are critical
While vitamin D may have benefits, Manson emphasized that it is not a cure-all. There are many chronic diseases that do not seem to be reduced by vitamin D supplementation, she said.
'Dietary supplements will never be a substitute for healthy diet and healthy lifestyle, and we've made it very clear time and again that the focus should be on the diet and lifestyle rather than on supplementation,' she said. 'However, targeted supplementation for people who have higher levels of inflammation or a higher risk of chronic diseases clearly related to inflammation, those high risk groups may benefit from targeted vitamin D supplementation.'
The telomere study was randomized, meaning participants were randomly assigned to either the vitamin D supplement group or the placebo group to ensure that characteristics such as age, health status, diet and lifestyle are balanced between the groups. Randomization is considered the gold standard in clinical research because it makes the groups as similar as possible at the start of the study.
'All of the risk factors for chronic disease, for telomere shortening, the age, the demographics, the physical activity, diet, underlying health, hypertension, diabetes, all these risk factors are balanced out by the randomization process,' Manson said, meaning the only difference between the two groups was that one received vitamin D and one did not. And the study was also 'double-blinded,' meaning that not only did the participants in each group not know which was receiving the supplement, but neither did the technicians administering it.
What other research and experts say
Not all studies have been as promising with regard to telomere preservation. A paper published in 2023 in the Journal of Nutrition, Health and Aging, for instance, concluded that 'routinely supplementing older adults, who are largely vitamin D replete, with monthly doses of vitamin D is unlikely to influence telomere length.'
Between 2014 and 2020, researchers at the QIMR Berghofer Medical Research Institute in Brisbane, Australia, led a randomized, double-blind, placebo-controlled trial of 1,519 participants, to see whether vitamin D supplementation would affect telomere length. They gave the supplement monthly to half of the participants and found no difference between those who received it and those who did not.
Carol Greider, a professor at the University of California at Santa Cruz who won the 2009 Nobel Prize in physiology or medicine for her discovery of telomerase, an enzyme that protects telomeres from shortening, said in an email that she was skeptical of the new study's findings.
Quantitative polymerase chain reaction, or qPCR, an assay that was used in the recent study to measure telomere length, has been shown in a number of publications to be unreliable, Greider wrote. The clinical standard for measuring telomere length is a technique called Flow FISH, which is highly reproducible.
Greider also noted that different subtypes of blood cells have different telomere lengths, so any changes in the cell type distribution in the blood could raise or lower the blood's average telomere length, not because the length changed but because the types of cells present changed.
She cited a perspective published in Aging Cell in March, in which the authors question research from 2024 that suggested spaceflight, like the Inspiration4 mission, which lasted just three days, increased the average telomere length of the white blood cells of those on the flight.
It's not that the telomeres are longer, the authors of the Aging Cell article wrote; it's that the composition of their white blood cells changed, raising the average telomere length.
'So while there may or may not be an effect of Vitamin D on telomeres, the methods used in this study are unlikely to be able to accurately document those changes without any control for cell type distributions,' Greider wrote.