Effects of Elevated Parathyroid Hormone Levels on Muscle Health, Postural Stability and Quality of Life in Vitamin D-Insufficient Healthy Women: A Cross-Sectional Study

Independently of plasma 25-hydroxyvitamin D (P-25(OH)D) levels, elevated parathyroid hormone (PTH) levels may exert an adverse effect on muscle health, postural stability, well-being, and quality of life. Using a cross-sectional design, we investigated 104 healthy postmenopausal women with low P-25(OH)D (< 50 nmol/l) levels, who had either secondary hyperparathyroidism (SHPT) with elevated PTH levels (> 6.9 pmol/l, n = 52) or normal PTH levels (n = 52). The average PTH value in women with SHPT was 8.5 (interquartile range 7.5-9.7) pmol/l and 5.3 (4.4-6.3) pmol/l in women with normal PTH (p < 0.001). Plasma phosphate was significantly lower in women with SHPT than in women with normal PTH (1.01 +/- 0.14 vs. 1.09 +/- 0.13 mmol/l; p < 0.01). In the total cohort, average level of 25(OH)D were 38 (31-45) nmol/l, with no differences between groups. SHPT was associated with impaired muscle strength as assessed by both maximum muscle strength and maximum force production at knee flexion with the knee fixed at 60 degrees and 90 degrees (p(all) < 0.05). Postural stability was impaired during semi tandem standing (p = 0.001). However, the two groups did not differ in terms of self-reported physical activity, muscle-related symptoms, quality of life, or lean muscle mass as assessed by dual-energy X-ray absorptiometry. Independently of 25(OH)D levels, mild to moderately elevated PTH levels are associated with adverse effects on muscle strength and postural stability. Why some individuals respond to vitamin D insufficiency with an elevated PTH and others do not need further elucidation, but elevated PTH itself seems to affect muscle function and postural stability.