An April 2021 study by Garvan Institute of Medical Research, Australia, said
"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."
"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."