Taking vitamin D supplements does not have a beneficial effect on muscle function, strength, or mass, according to an analysis published in the Journal of Bone and Mineral Research

The study analysed all available data from relevant, randomised, controlled clinical trials, using data from 54 trials involving more than 8,740 individuals. 

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Overall, the researchers found that there were no benefits of vitamin D supplementation over placebo for improving muscle health.

Vitamin D supplementation appeared to have detrimental effects on some physical performance measures

The researchers measured physical performance using the Timed Up and Go test (TUG), chair rising test, 6-minute walking distance, and Short Physical Performance Battery (SPPB). 

They also considered participants' maximum muscle strength, measured at handgrip, elbow flexion, elbow extension, knee flexion, and knee extension, as well as muscle mass.

The analysis found that, instead, vitamin D appeared to have detrimental effects in terms of increased time spent performing the TUG test, a decrease in maximum strength at knee flexion, and a tendency towards a reduced score of the SPPB.

Other measures of muscle health did not show between-group differences. In subgroup analyses, including studies with low vitamin D levels, effects of vitamin D supplementation did not differ from placebo.

"Care should be taken recommending vitamin D supplementation to improve muscle strength and function"

Lead author of the study, Lise Sofie Bislev of Aarhus University Hospital, Denmark, said: “Care should be taken recommending vitamin D supplementation to improve muscle strength and function in people with normal or only slightly impaired vitamin D status.

"We need to study further whether it may benefit muscles in those with severe vitamin D deficiency, however.”