Vitamin D Didn't Move Two Longevity Markers in 7 Trials

Jeff's Daily Pick. Vitamin D is sold as an anti aging supplement. Pooled across seven trials, it did not significantly change two blood markers tied to exercise and longevity.

In Iran, a team led by Sajjad Moradi published a systematic review and meta analysis in BMC Endocrine Disorders on August 31, 2026 asking whether vitamin D supplements change two circulating markers often discussed in longevity circles: irisin, a hormone released by muscle during exercise, and SIRT1, a sirtuin enzyme linked to cellular aging pathways.

The pooled result

The authors included seven randomized controlled trials with nine arms. Against placebo, vitamin D produced no statistically significant change in irisin (weighted mean difference 1.84 ng/ml; 95% CI minus 0.25 to 3.93; p = 0.084) or in SIRT1 (1.57 ng/ml; 95% CI minus 0.18 to 3.31; p = 0.078). Heterogeneity was very high, with I squared values of 95.0% and 92.3%, meaning the trials disagreed with each other far more than chance would explain.

The subgroups

Some subgroups did show increases: irisin rose in trials of people with type 2 diabetes (p = 0.029) and in studies conducted in Iran (p = 0.025), and SIRT1 rose in 12 week trials (p = 0.008). A subgroup on 7,000 IU a week also showed a SIRT1 increase, but it rested on a single effect size, and the authors label it exploratory. With seven trials and that much heterogeneity, subgroup findings are hypotheses, not results.

The pattern is familiar. Large trials of vitamin D for hard outcomes have mostly been null outside deficiency: a separate 2026 meta analysis of five trials and 56,901 participants found no effect on melanoma incidence or recurrence. Irisin and SIRT1 add another null at the level of blood markers. Our piece on diet, exercise and supplements compares what moves aging markers and what does not.