Does Vitamin D2 or D3 Benefit or Damage Muscles?

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Many observational studies in medical literature support the overall benefits of vitamin D supplementation. However, whether this is actually true is the subject of a renewed debate, particularly in muscle health.

A consensus of published literature did not support vitamin D supplementation for promotion of muscle health and indicated that supplementation may cause adverse effects in some cases. These findings, from a systematic review and meta-analysis, were published in the Journal of Bone Mineral Research.

Researchers from Aarhus University Hospital in Denmark performed a search in October 2020 of online medical literature for studies of the effect of vitamin D supplementation  on muscle health and function using search terms such as ‘muscle strength’, ‘muscle function’ and ‘vitamin D’, among others.

A total of 54 studies randomized control trials comprising 8747 individuals were included in this analysis. Participants were dominated by postmenopausal women; 3 of the studies recruited only men and 3 recruited only children. Muscle health was most commonly assessed by handgrip strength (n=35), knee extension (n=20), and timed up and go (n=19) tests. Vitamin D supplementation was administered for ³26 weeks in 33 of the studies.

Vitamin D supplementation was found to significantly improve up and go time among 5223 participants (mean difference, 0.15; 95% CI, 0.03-0.26; P =.01) and to significantly reduce knee flexion among 765 individuals (mean difference, -3.33; 95% CI, -6.63 to -0.03; P =.05).

No significant effect was reported for short physical performance battery, chair rising test, 6-minute walking distance, handgrip, elbow extension, elbow flexion, knee extension, or total lean mass.

Among the subset of studies which used differing doses of vitamin D, no significant effect between high and low doses were observed vs placebo. Similarly, co-supplementation with calcium, stratifying vitamin D2 from D3, or stratifying studies on date of publication did not alter the overall findings.

Researchers acknowledged their study may have been limited by the fact that supplementation was administered for ≥6 months in the majority of studies, nor did they include patients with severe vitamin D deficiency.  It remains unclear whether differing effects would be observed with long-term exposure.

Additionally, these data did not support the use of supplemental vitamin D2 or D3 with or without calcium, as there was little evidence for improved muscle health. Some evidence suggested that supplementation may in fact damage muscle health by reducing knee flexion.

“Given the enormous public interest in vitamin D supplementation, we need to be aware of uncritical use of vitamin D,” the researchers said. “Identifying safe repletion regimens is warranted.”


Bislev LS, Grove-Laugesen D, Rejnmark L. Vitamin D and muscle health: a systematic review and meta-analysis of randomized placebo-controlled trials. J Bone Miner Res. 2021;36(9):1651-1660. doi:10.1002/jbmr.4412