Vitamin D, best known for maintaining calcium balance and bone health, is critical in many physiological processes, including blood pressure regulation, immune function, and cell growth. Evidence now suggests vitamin D also influences body composition and muscle strength. A recent study in mice showed that high vitamin D intake increased muscle strength and mass without altering body weight.

Researchers fed mice one of three diets, providing low, normal, and high doses of vitamin D for four weeks to achieve deficient, insufficient, and sufficient vitamin D concentrations, respectively. At the end of the fourth week, they assessed the animals' grip strength (a measure of muscle function) and body composition.

They found that compared to low or normal vitamin D intake, high intake increased grip strength and lean mass and decreased fat mass without altering the animals' weights. High intake also impaired myostatin production and increased the animals' leptin sensitivity and energy expenditure without altering their activity levels.

Leptin is a satiety hormone that signals the brain to balance energy. When body fat increases or decreases, blood concentrations of leptin change accordingly. Higher leptin levels signal the brain to reduce hunger and boost energy use. However, in obesity, the body becomes less responsive to leptin, dulling its effects on appetite and energy expenditure.

These findings suggest that vitamin D influences body composition and metabolism by preferentially allocating calories toward muscle development and overall growth rather than fat storage. They also highlight the intricate relationship between obesity and vitamin D status. Learn more about vitamin D in our comprehensive overview article.