Vitamin D deficiency may impair muscle function, finds study

Dr Andrew Philp and his team at the Garvan Institute of Medical Research in Australia, and collaborating universities, used a mouse model to determine the effects of diet-induced vitamin D deficiency on skeletal muscle mitochondrial function in young, male mice. Mice were either fed a diet with normal quantities of vitamin D, or with no vitamin D to induce deficiency, for a period of 3 months. A typical vitamin D level for humans is 40-50 nmol.L-1, and acute vitamin D deficiency is diagnosed when levels drop below 12 nmol.L-1. On average, the mice in this study had vitamin D levels of 30 nmol.L1, with diet-induced vitamin D deficiency leading to levels of just 3 nmol.L-1. Although this level was more extreme than typically observed in people, it is still within the clinically-recognised range. Tissue and blood samples were collected monthly to quantify vitamin D and calcium concentrations and to assess markers of muscle mitochondrial function and number. After 3 months of diet-induced vitamin D deficiency skeletal muscle mitochondrial function was found to be impaired by up to 37%. This was not due to a reduced number of mitochondria or a reduction in muscle mass.

"Our results show there is a clear link between vitamin D deficiency and oxidative capacity in skeletal muscle. They suggest that vitamin D deficiency decreases mitochondrial function, as opposed to reducing the number of mitochondria in skeletal muscle." Dr Philp comments. "We are particularly interested to examine whether this reduction in mitochondrial function may be a cause of age related loss in skeletal muscle mass and function."

These findings suggest that vitamin D deficiency may impair mitochondrial function and reduce the amount of energy produced in the muscles, which may lead to poor muscle function. Therefore, preventing vitamin D deficiency in older people may help maintain muscle performance and reduce the risk of muscle related diseases, such as sarcopenia. However, further studies that investigate the direct effect of vitamin D deficiency on muscle function and strength are necessary to confirm this.

Whilst this study indicates that vitamin D deficiency can alter mitochondrial function in skeletal muscle, Dr Philp and his team were unable to determine precisely how this process occurred. Therefore, their future work aims to establish how vitamin D deficiency alters mitochondrial control and function in skeletal muscle.