Vitamin D supplements taken daily appear to preserve the length of telomeres in cells, a marker of biological aginganilakkus/Getty Images
It’s well known that vitamin D is crucial for maintaining strong bones. The nutrient helps your body absorb and retain calcium and phosphorus, minerals used to build bone.
It also plays an important role in immune system health, cognition and muscle and nerve function.
Now, a new study suggests vitamin D has yet another protective role: helping our cells live longer.
According to the findings, taking a daily vitamin D supplement preserves the length of telomeres in cells, a marker of biological aging.
Here’s what you need to know about the research – and why it’s too soon to broadly recommend vitamin D to delay cell aging.
What are telomeres?
Telomeres are protective caps of DNA on the ends of chromosomes. Like the plastic tips on the ends of shoelaces, telomeres prevent the ends of chromosomes from unravelling or sticking together.
They also protect the DNA in chromosomes during cell division, allowing cells to divide without losing genetic material.
Every time cells divide – crucial for growth and cellular repair – their telomeres become slightly shorter. Eventually, they become so short that the cells can no longer divide and become inactive or die.
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Telomere shortening is associated with aging, as well as an increased risk of age-related chronic illness, including cardiovascular disease, type 2 diabetes, cancer and Alzheimer’s disease.
Smoking, chronic stress, an unhealthy diet, lack of physical activity and exposure to pollution have been implicated in accelerated telomere shortening.
Previous observational studies have found protective associations between vitamin D and telomere length. A handful of small, short-term clinical trials have also found beneficial effects of vitamin D supplementation on telomere length.
About the latest research
The new findings, published last month in the American Journal of Clinical Nutrition, come from a large-scale randomized controlled trial called VITAL, which ended in December, 2017. VITAL is an acronym for VITamin D and OmegA-3 TriaL.
The VITAL trial, which ran for more than five years, tested whether vitamin D3 (2,000 IU per day) and/or omega-3 fatty acids from fish oil (one gram per day) lowered the risk of heart disease, stroke or cancer in 25,871 healthy U.S. males and females aged 50 and older.
The new VITAL Telomere study analyzed data from 1,031 VITAL participants whose telomere length in white blood cells was measured at the start of the study and again at years two and four.
In the placebo group, the researchers observed substantial telomere shrinkage at year two and again at year four.
Among the participants taking 2,000 IU of vitamin D a day, telomere shortening was minimal throughout the study.
Compared to the placebo, vitamin D significantly reduced telomere shrinkage over four years by an amount the researchers suggested was equivalent to preventing three years of aging.
Omega-3 supplementation had no significant effect on telomere length.
The findings remained unchanged after controlling for other potential risk factors, including age, sex, body mass index and smoking status.
A limitation of the study is that VITAL participants were mostly white and had an average age of 65, so the findings may not apply to other groups.
How vitamin D may protect telomeres
It’s unclear how vitamin D may preserve telomere length.
Some research has shown that it increases the activity of telomerase, an enzyme that lengthens telomeres.
As well, vitamin D’s antioxidant and anti-inflammatory properties are thought to protect telomeres by shielding them from oxidative stress. Telomeres are particularly vulnerable to DNA damage caused by free radicals.
A 2023 review of 25 human and animal studies concluded there was a strong link between vitamin D and reduced DNA damage.
More research warranted, vitamin D intake recommendations
The new VITAL findings are promising.
However, the researchers acknowledged that their findings need to be confirmed by further large-scale randomized trials, particularly in other racial and ethnic groups.
The daily recommended intakes for vitamin D, which are based on the amount required to maintain bone health in healthy people, are 400 IU for infants, 600 IU for ages one to 70 and 800 IU for older adults. Health Canada recommends that adults 50 and older take a daily 400 IU vitamin D supplement.
Some people may need more to maintain a sufficient blood level. Sun exposure, diet, skin colour, age and excess body weight influence vitamin D status.
Osteoporosis Canada recommends year-round vitamin D supplementation because there is insufficient UVB radiation from sunlight to produce vitamin D in the skin from mid-October through to mid-March. Plus, very few foods contain the nutrient.
The Linus Pauling Institute at Oregon State University recommends healthy adults take 2,000 IU of supplemental vitamin D daily.
The safe upper limit for vitamin D has been set at 4,000 IU per day for individuals nine and older; it is lower for younger children and infants.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on X @LeslieBeckRD
