Background and Objectives: Sarcopenia is explained as the loss of muscle strength and muscle mass with aging‚ and is one of the major risk factors for metabolic diseases. Cross-sectional studies demonstrate that vitamin D is associated with sarcopenia in both men and women. The aim of this study was to investigate the effect of vitamin D supplement consumption on muscle strength, muscle function and body composition in middle-aged women.

Materials and Methods: In this randomized double-blind placebo-controlled trial, 71 women aged 40-55 years old, with the serum 25(OH)-D <25 ng/ml, were divided in two groups randomly, and received a 1000 IU vitamin D tablet (n=37) or a placebo (n=34), daily for 12 weeks. At the beginning and at the end of the study, dietary intake, anthropometric indices, muscle strength and function, serum 25(OH)-D, physical activity level and sun exposure were assessed. Statistical analysis was performed with SPSS version 20.

Results: A significant difference in serum 25(OH)-D was found between the intervention and placebo groups at the end of the study (P<0.001). In the vitamin D group, handgrip strength was improved, while hand grip strength (P=0.233) and knee extension strength (P=0.337) between the two groups did not differ significantly after 12 weeks. The mean of timed get up and go test, decreased significantly in the vitamin D group compared to the controls (P<0.001). Within the intervention group, body fat content decreased significantly after 12 weeks (P<0.001), but did not result a significant difference between the two groups (P=0.051).

Conclusions: It seems in this vitamin D-deficient middle-aged women group, 1000 IU vitamin D consumption daily for 12 weeks resulted in improvement of muscle function and body composition, but had no significant effect on muscle strength.

Keywords: Vitamin D, Muscle strength, Muscle function, Middle-aged women