Influences of dietary vitamin D restriction on bone strength, body composition and muscle in rats fed a high-fat diet: involvement of mRNA expression of MyoD in skeletal muscle.

Vitamin D insufficiency is associated with a greater risk of osteoporosis and also influences skeletal muscle functions, differentiation and development. The present study investigated the influences of vitamin D restriction on the body composition, bone and skeletal muscle in rats fed a high-fat diet. Sprague-Dawley strain male rats (11weeks old) were divided into four groups and fed experimental diets: a basic control diet (Cont.), a basic control diet with vitamin D restriction (DR), a high-fat diet (F) and a high-fat diet with vitamin D restriction (FDR). At 28days after starting the experimental diets, the visceral fat mass was significantly increased in the F group compared with Cont. group, and the muscle mass tended to decrease in the DR group compared with Cont. group. The total volume of the femur was significantly lower in the DR group compared with Cont. group, and the bone mineral density (BMD) of the femur was significantly lower in the FDR group compared with F group. MyoD is one of the muscle-specific transcription factors. The levels of mRNA expression of MyoD of the gastrocnemius and soleus muscles from the DR group were reduced markedly compared with those from the Cont. group. In conclusion, our findings revealed the influences of a vitamin D-restricted high-fat diet on the bone strength, body composition and muscle. Further studies on vitamin D insufficiency in the regulation of muscle as well as fat and bone metabolism would provide valuable data for the prevention of lifestyle-related disorders, including osteoporosis and sarcopenia.