Associations between serum 25-hydroxyvitamin D level and skeletal muscle mass and lower limb muscle strength in Japanese middle-aged subjects.

Objectives: One of the important risk factors of falling is decreased muscle mass and muscle strength. Recently, there has been an increasing concern on the role of vitamin D in muscle strength and physical activity. Aim of our study is to examine the relationships between vitamin D status and muscle mass and muscle strength in middle-aged healthy adults.

Methods: Subjects were 40 healthy volunteers aged 42.0 ± 10.6 years old. Evaluation was made for serum vitamin D metabolites including 25-hydroxyvitamin D [25(OH)D] and 24,25-dihydroxyvitamin D [24,25(OH)D] concentrations, lower limb muscle strength, and dietary intake by food frequency questionnaire. Body composition was measured by dual-energy X-ray absorptiometry (DXA), and appendicular skeletal mass index (ASMI) was calculated as skeletal muscle mass/squared height.

Results: 70% of the subjects had vitamin D insufficiency/deficiency (serum total 25(OH)D < 20 ng/mL), and female subjects had significantly lower serum total 25(OH)D level compared with males. Vitamin D insufficiency/deficiency group had significantly higher body fat, lower SMI and muscle strength, probably reflecting higher percentage of female subjects. Serum vitamin D metabolites levels were significantly correlated with whole and site-specific ASMI, and lower limb muscle strength, except for the correlation between serum 24,25(OH)D concentration and lower limb muscle strength. In addition, serum 25(OH)D level was a positive significant predictor for both ASMI and lower limb muscle strength, while serum 24,25(OH)D level was not their significant predictor.

Conclusions: Serum 25(OH)D level was significantly correlated with both skeletal muscle mass and lower limb muscle strength.