Relationship between age-associated endocrine deficiencies and muscle function in elderly women: a cross-sectional study

Objective: muscle receptors and selected anabolic effects have been identified for both insulin-like growth factor I (IGF-I) and 1,25-dihydroxyvitamin D (1,25(OH)(2)D-3). The aim of the present study was to test the hypothesis that the decreasing concentrations of these endocrine factors might be involved in the decline in muscle function that characterizes normal human ageing. Design: cross-sectional study. Study participants: a community-based sample of 245 healthy elderly women aged 70-90 years. Exclusion criteria mere diseases or medications known to affect muscle function or the somatotrophic axis. Measurements: knee extension strength was evaluated using an isokinetic dynamometer. A standardized questionnaire was used to assess habitual physical activity. IGF-I and 1,25(OH)(2)D-3 were measured by radioimmunoassay. Vitamin D binding protein (DBP) was measured by single radial immunodiffusion and the free 1,25(OH)(2)D-3 concentration calculated as the molar ratio of total 1,25(OH)(2)D-3 to DBP. Results: the differences in isometric and isokinetic strength over the age range were equivalent to losses of 0.9-2.4% per year. However, no relationship was found between the somatotrophic axis or vitamin D status and knee extension strength, despite markedly decreasing concentrations of circulating IGF-I and free 1,25(OH)(2)D-3 with age. Conclusion: levels of circulating IGF-I and free 1,25(OH)(2)D-3 appear not to be involved in the loss of muscle function that characterizes normal human ageing.