Physical activity, osteoporosis, and fracture risk : long-term associations in a general population
Year: 2011
Type: dissertation
Study design: Observational Study
Abstract: Osteoporosis and related fractures are a major health problem among elderly people, and Norway has reportedly one of the highest fracture rates in the world. Many factors contribute to osteoporosis and fractures. One highly relevant protective factor is physical activity, which is a major mechanical determinant of the properties of the skeleton. Physical activity may postpone the age-related bone loss and decrease the risk of falling, and thereby reduce the risk of osteoporotic fractures. \nBecause osteoporosis and fractures primarily occur in the elderly, it is of interest to observe the long-term benefits of physical activity. The Tromsø Study, which is a population study with recurrent surveys, provides an excellent opportunity to follow people throughout adulthood into older age. Thus, the aim of this thesis was to examine the long-term associations between physical activity and outcomes such as bone mineral density (BMD) (paper II) and risk of non-vertebral fracture (paper III) in adults. Moreover, to form a basis for these associations, the stability (i.e. tracking) of physical activity habits over three decades was investigated (paper I). In all three papers, longitudinal data were derived from the surveys in the Tromsø Study. Adult women and men were followed throughout adulthood into older age. \nAnalyses of tracking of physical activity indicated that physical activity habits during adulthood are relatively stable (i.e. track) over time (paper I). Sedentary adults have markedly higher odds of being sedentary later in life than active adults. The same were true for the other physical activity levels, i.e. being physically active in adulthood is a strong predictor of being active later in life. The results from this study have implications for the subsequent studies in this thesis. \nIn paper II, examination of the associations between physical activity and BMD showed a positive linear trend in BMD across physical activity levels. The differences in BMD between physical activity groups were rather small, but consistent over different sites of the hip and forearm, and even small differences in BMD can have relatively large effects on fracture risk. \nThe results from paper III showed that moderate and high physical activity appeared protective against fractures in the weight-bearing (lower) skeleton, whereas the risk of fracture in the non-weight-bearing skeleton was not related to physical activity level, indicating that effects of physical activity on fracture risk are site-specific. \nThese population studies suggest that physical activity can prevent or delay osteoporosis and age-related fractures, and that the mechanisms partly involve bone mineral density, as physical activity was related to BMD in a dose-response pattern. Moreover, there is a tendency that physical activity habits in adults are fairly stable over a long time. This implies that adults who are sedentary tend to stay sedentary later in life, which may be worrying considering the many health benefits of physical activity.
Author: Bente Morseth
Language: English
Subfield: Orthopedics and Sports Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
Funder: Norges Forskningsråd
OpenAlex ID: W635837282