Vitamin D supplementation does not have any beneficial effects on muscle function, strength, or mass. At the same time, it also has harmful effects on muscle health.
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On the contrary, vitamin D appeared to have harmful effects in terms of increased time spent performing, which is called as Timed Up and decreases maximum strength at knee flexion, and a tendency towards a reduced score of the Short Physical Performance Battery.
These results show that care should be taken while 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.
Source-Medindia