Associations between serum 25-hydroxyvitamin D(3) 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(3) metabolites including 25-hydroxyvitamin D(3) [25(OH)D(3)] and 24,25-dihydroxyvitamin D(3) [24,25(OH)(2)D(3)] 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(3) 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)(2)D(3) concentration and lower limb muscle strength. In addition, serum 25(OH)D(3) level was a positive significant predictor for both ASMI and lower limb muscle strength, while serum 24,25(OH)(2)D(3) level was not their significant predictor. CONCLUSIONS: Serum 25(OH)D(3) level was significantly correlated with both skeletal muscle mass and lower limb muscle strength.