Genetic and Environmental Influences on Bone and Fractures

Sammanfattning: Sweden and Norway have the worldwide highest incidence of osteoporotic fractures. As these fractures constitute a tremendous and growing problem, primary prevention is of great importance. The principal causes of an osteoporotic fracture are a fall and a fragile skeleton. The aim of the studies reported in these papers was therefore to determine the genetic and environmental influences on fractures and the genetic influence on the two main reasons to the emergence of osteoporotic fractures; bone mineral density and propensity to fall.In the present thesis, we display that the heritability of fractures is dependent on fracture site and age. With increasing age, lifestyle becomes the dominant explanatory factor. These results indicate that focus should be on lifestyle interventions for the prevention of fractures in the elderly.Although the genetic liability to impaired balance is modest, twins with self-reported impaired balance have a substantially increased risk of osteoporotic fractures compared to their co-twin without impaired balance. Asking a patient about his or her balance might be a simple tool for future risk assessment.The genetic influence on bone phenotypes is under strong genetic influence in Swedish adult twins. These findings are in agreement with the results from previous studies in other countries, with a lower incidence of osteoporotic fractures compared to Sweden. The high heritability of bone phenotypes together with the low heritability of fractures at old age, indicates that bone mineral density has a modest influence on fracture risk at old age.In summary, based on the results in this thesis, more emphasis should be targeted to the prevention of falls, by strength and balance training in order to prevent the occurrence of  low energy fractures in the elderly.