Vitamin D3 or omega-3 fatty acids: which supplement slows decay of leukocyte telomere length? 4-year findings from the VITAL trial

Introduction

Telomeres are protective caps at the ends of chromosomes that help maintain the stability of our DNA. Over time, these telomeres naturally become shorter as cells divide. When they become too short, cells can no longer function properly and may die or become damaged, which contributes to aging and the development of chronic diseases. Some earlier studies suggested that nutrients like vitamin D and omega-3 fatty acids might help slow this shortening process, but the evidence from large, long-term clinical trials has been limited and inconsistent. This study aimed to examine whether daily supplementation with vitamin D3 or marine omega-3 fatty acids could help slow down telomere shortening in adults over a four-year period.

Study Design

The study was part of a larger clinical trial called VITAL, which involved over 25,000 U.S. adults. For this particular analysis on telomere length, 1,031 participants were followed closely over four years. The participants were randomly assigned to receive either vitamin D3 (2,000 IU per day), omega-3 fatty acids (1 gram per day), both supplements, or a placebo (no active supplements). The trial was randomized, double-blind, and placebo-controlled, meaning neither the participants nor the researchers knew who was receiving which treatment. Telomere length in white blood cells was measured at the beginning of the study, after two years, and after four years using a laboratory technique called quantitative polymerase chain reaction.

Results

After analyzing 2,571 blood samples from the 1,031 participants, the researchers found that people who took vitamin D3 supplements experienced significantly less telomere shortening over the four-year period compared to those who did not take vitamin D. Specifically, telomere length declined 0.14 kilobase pairs less in the vitamin D group, which is equivalent to preserving about 140 base pairs of telomere length. This suggests a modest protective effect of vitamin D against cellular aging. In contrast, participants who took omega-3 fatty acids did not show any significant difference in telomere length compared to the placebo group, either at the two-year or four-year mark.

Discussion

The findings suggest that daily supplementation with vitamin D3 over four years may help reduce the rate of telomere shortening, which could have implications for slowing cellular aging and reducing the risk of age-related diseases. Although the observed benefit was relatively small, it was statistically significant and adds to the growing evidence that vitamin D may play a role in supporting long-term health at the cellular level. On the other hand, the results showed no benefit of omega-3 fatty acids for preserving telomere length, indicating that not all nutritional supplements have the same effects on biological aging. These results highlight the potential of vitamin D supplementation as a simple and safe intervention to support healthy aging, but more research is needed to fully understand the long-term health consequences and mechanisms involved.

This study reinforces the idea that vitamin D3 may be beneficial beyond bone health, particularly in helping to maintain the integrity of our DNA as we age.

If you want to possibly age a little slower on the inside, vitamin D3 might help. Fish oil? Not so much—for telomeres, anyway.

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Zhu H, Manson JE, Cook NR, Bekele BB, Chen L, Kane KJ, Huang Y, Li W, Christen W, Lee IM, Dong Y. Vitamin D₃ and marine ω-3 fatty acids supplementation and leukocyte telomere length: 4-year findings from the VITamin D and OmegA-3 TriaL (VITAL) randomized controlled trial. Am J Clin Nutr. 2025 May 21:S0002-9165(25)00255-2. doi: 10.1016/j.ajcnut.2025.05.003. Epub ahead of print. PMID: 40409468.