Participants in the vitamin D3 group took daily 2,000 IUs of the supplement, which is a dosage commonly found over-the-counter at neighborhood pharmacies.
Researchers looked for signs of aging in participants’ cells, which split as they replicate. Over a whole lifetime, a person’s chromosomes may appear more frayed because the cells have replicated so many times, scientists said. The authors also looked for anti-aging effects of fatty acids, but that part of the study found “no significant effect.”
The biggest discovery came when researchers saw that the chromosomes of people who took daily vitamin D3 pills appeared younger than those of the control group, said study author JoAnn Manson.
“It was intriguing that we found that vitamin D supplementation did protect against a key pathway of biological aging,” said Manson, a medical professor at Harvard and Brigham and Women’s Hospital.
Specifically, protective caps on the ends of chromosomes — which have long been known to shorten with age — measured longer at the end of the study in the vitamin D3 group, according to the study.
The shortening of the protective caps, called telomeres, is an “aging biomarker” that signals someone is more prone to inflammation and disease, Manson said.
Shorter telomeres lead the entire X-shaped chromosome to deteriorate with age, “which increases risks for chronic diseases, cancer, cardiovascular disease, and overall mortality,” the study said.
Michael Holick, a national expert on vitamin D, said the study’s findings are consistent with other research showing people with insufficient vitamin D3 levels are at higher risk for cardiovascular disease, Type 2 diabetes, and even infectious diseases.
“These data are very supportive of the fact that it definitely improves health outcomes,” said Holick, a professor at the Boston University School of Medicine who was not involved in the study.
On average, study participants who took daily vitamin D3 for four years had telomere lengths consistent with only one year of aging over that period, the study found. The telomeres of participants in the placebo group had average lengths consistent with four years of aging, scientists said.
“Over four years, there was protection against three years of biological aging through that pathway of telomere shortening, which was an intriguing finding,” Manson said.
Importantly, the study findings do not trump what doctors and scientists have long told patients about naturally occurring forms of vitamin D, Manson said.
“Most importantly, we are recommending that people try to follow a healthy diet that’s high in fruits, vegetables, and whole foods, and really minimize processed and ultra-processed foods,” she said.
Vitamin D supplements will never outweigh the positive biological effects of healthy diet and exercise regimens, which provide the human body with sufficient vitamin D, Manson said.
“We do believe that a healthy diet healthy lifestyle are paramount and will never be replaced by popping any pill,” she said.
Still, the study findings are important because they provide some proof that supplementing vitamin D intake in the winter months can have benefits at the cellular level, Manson said. People who have chronic conditions that prevent them from eating certain vitamin D-rich foods can also use vitamin D pills to effectively fill a nutritional gap, she said.
“It’s quite reasonable, as a form of insurance to take 1,000 to 2,000 IUs a day if you have concerns about getting adequate intake from the diet or time spent outdoors,” Manson said.
Holick, who is known for discovering the major form of vitamin D that circulates in human blood, said he recommends his patients take at least 2,000 IUs of vitamin D3 daily.
“The data is very clear — if you are vitamin D deficient, you’re at more increased risk of mortality,” he said.
Claire Thornton can be reached at claire.thornton@globe.com. Follow Claire on X @claire_thornto. Camilo Fonseca can be reached at camilo.fonseca@globe.com. Follow him on X @fonseca_esq and on Instagram @camilo_fonseca.reports.
