It seems a new study about the benefits of vitamin D comes out every week. Even doctors who have a bias against nutrition have to admit that testing and treating vitamin D deficiency is important for the prevention of many diseases! I routinely test blood vitamin D levels (along with other nutrients) of patients and commonly find that people have low or deficient levels.

The current study was part of a larger study known as the  VITamin D and OmegA-3 TriaL (VITAL). The study involved giving vitamin D3 (2000 IU per day) and omega-3 fatty acids (1 gram) to many thousands of adult females and males. The research already showed that daily supplementation with vitamin D3 but not omega 3, resulted in a reduced incidence of advanced cancer by 17% and reduced all incident autoimmune disease by 22% compared to placebo.

DNA Study

In this recent study, researchers from Harvard looked at whether taking vitamin D3 and omega-3 fatty acids (like in fish oil) for 4 years could help slow down damage to our DNA as we age. Our DNA has special protective tips called telomeres, kind of like the plastic ends of shoelaces. These tips get shorter as we get older, and shorter telomeres are linked to aging and age-related diseases, including cancer, cardiovascular disease, and overall mortality. 

In this part of the study, researchers gave more than 1,000 healthy adults one of the following:

• Vitamin D3 (2,000 IU per day),
• Omega-3 fatty acids,
• Both together,
• Or a placebo (fake pill).

After 4 years, they checked the telomere length in white blood cells (leukocytes).

What they found:

• People who took vitamin D3 had slower shortening of their telomeres.
• Omega-3s didn’t make a clear difference on their own.
• This suggests that vitamin D3 might help protect cells from aging.

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Conclusion:

Taking vitamin D3 daily for 4 years may help slow down cell aging by protecting the ends of DNA (telomeres). It could be useful for staying healthier as we get older. Make sure to get your blood vitamin D levels tested.

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Reference

Zhu, H., Manson, J. E., Cook, N. R., Bekele, B. B., Chen, L., Kane, K. J., Huang, Y., Li, W., Christen, W., Lee, I. M., & Dong, Y. (2025). Vitamin D₃ and Marine Omega-3 Fatty Acids Supplementation and Leukocyte Telomere Length: 4-Year Findings from the VITAL Randomized Controlled Trial. The American journal of clinical nutrition, S0002-9165(25)00255-2. Advance online publication. https://doi.org/10.1016/j.ajcnut.2025.05.003

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