Background: Elderly people experience a gradual loss of muscle strength and a reduction of serum levels of vitamin D and of vitamin D receptor expression in skeletal muscle cells.
Aims: The aim of our study was to evaluate the association among serum levels of 25-hydroxy-vitamin D [25(OH)D3], muscle strength, and physical performance in post-menopausal women.
Methods: In our retrospective case-control study, we analyzed data from medical records of post-menopausal women aged ≥ 50 years. We compared subjects with hypovitaminosis D [25(OH)D3 <30 ng/ml] vs. those with normal levels [25(OH)D3 ≥ 30 ng/ml]. Outcome measures were: Hand Grip Strength Test (HGS) and Knee Extension Strength Test (KES) to evaluate upper and lower limb muscle strength, respectively; Short Physical Performance Battery (SPPB) and usual 4-m gait speed (4 MGS) to evaluate physical performance.
Results: We examined 80 patients (mean aged 65.92 ± 7.69 years): forty-six subjects with hypovitaminosis D (mean aged 66.09 ± 7.71 years) and 34 with normal levels of vitamin D (mean aged 65.71 ± 7.78 years). There was a statistically significant difference between hypovitaminosis D group and subjects with normal levels of vitamin D in HGS (12.13 ± 4.34 vs. 19.14 ± 5.59; p < 0.001), KES (11.99 ± 4.04 vs. 16.98 ± 8.43; p = 0.003), SPPB score [8 (5.75-10.25) vs. 12 (10-12); p < 0.001], and proportion of patients with usual 4 MGS ≤ 0.8 m/s [29 (63.0%) vs. 9 (26.5%); p = 0.002].
Discussion: In literature, there is no agreement on the association among serum vitamin D levels and muscle function. Our data showed that post-menopausal women with hypovitaminosis D had worse upper and lower limb muscle strength and physical performance than subjects with normal levels of 25(OH)D3.
Conclusions: Our results support the hypothesis that there is a significant positive association among serum 25(OH)D3 levels and upper and lower limb muscle functioning.
Keywords: Hypovitaminosis D; Muscle strength; Physical performance; Skeletal muscle; Vitamin D.