Genetic and Environmental Contributions to Bone Structural Strength in Postmenopausal Women

Mikkola, Tuija Genetic and environmental contributions to bone structural strength in postmenopausal women Jyväskylä: University of Jyväskylä, 2010, 77 p. (Studies in Sport, Physical Education, and Health ISSN 0356-1070; 155) ISBN 978-951-39-4058-4 Finnish summary Diss. The purpose of this study was to investigate the genetic and environmental contributions to estimated bone structural strength in postmenopausal women. Specifically, the association of hip fracture history and postmenopausal hormone therapy (HT) to bone strength and its determinants were studied. In addition, the association of loading environment with bone properties was assessed. This study utilized three different datasets comprising bone measurements obtained using peripheral quantitative computed tomography. The participants in the first dataset were 103 monozygotic and 114 dizygotic 63to 76year-old female twin pairs. The participants in the second dataset were 60to 85-year-old women with a hip fracture history (n=38) and control women without hip fracture history (n=22). The participants in the third dataset were 24 monozygotic female twin pairs aged 54 to 72 years and discordant for HT. Genetic effects were found to account for 40 to 60% of the inter-individual differences in the estimated bone strength of the body weight-loaded lower limb and 80% of that of the non weight-loaded upper limb. The association between muscle cross-sectional area and bone strength was explained by both common genetic and common environmental factors. In women with hip fracture history, bone strength was significantly impaired in the tibia of the fractured leg, which impairment was largely explained by reduced muscle crosssectional area and muscle strength. The HT users had significantly higher bone strength in the upper and lower limb than their non-HT-using co-twins. This study shows that while genetic factors are important for bone strength in postmenopausal women environmental factors have considerable influence especially in the lower limbs. Bone strength is negatively influenced by hip fracture and positively by HT. The results also suggest that loading environment modifies the heritability of bone strength but not the influence of HT on bone strength. Muscle-induced loading may preserve bone strength after hip fracture.