Novel aspects of an old problem. The Norwegian Epidemiologic Osteoporosis Studies (NOREPOS)

Every hour, two new forearm fractures and one new hip fracture occur in Norway. Hip fractures are painful, reduce function, shorten life expectancy, and entail large healthcare costs. Although the risk of hip fracture has declined during the past couple of decades, an increase in the number of fractures is expected due to a growing elderly population. There are some well-established risk factors for fracture, but the question why Norway is the world leader remains unresolved. We use national hip fracture data in combination with health studies and registers covering the entire population to study factors considered important to reduce the number of fractures. The project has three work packages: In the first, we have developed a pioneer model for estimating the contribution of changes in risk factors and treatments over two decades to explain the decline in hip fracture incidence. Secondly, there is an intriguing link between the immune system and bone metabolism. In a very large sample from the general Norwegian population, we have found that the variation in tuberculin skin test responses after BCG vaccination as a measure of normal variation in immune function is related to long-term risk of hip fracture in men. Interestingly, no such clear association was observed in women. Based on these findings, we have been involved in studies assessing the association between variation in the immune system and other disease endpoints (multiple sclerosis and osteoarthritis of the hip respectively). In the third work package, we explore causes of geographic variations in fracture risk by combining data on weather conditions, climate changes, topography and air pollution with individual-level sociodemographic and fracture outcome data. For example, we have found that there is a clearly increased risk of forearm fractures at cold ambient temperatures (especially at temperatures around the freezing point). The corresponding association was somewhat weaker for hip fracture. On the other, an excess post–hip fracture mortality was found at cold ambient temperatures. The research is conducted by NOREPOS, a longstanding national research network comprising the four medical faculties in Norway and the Norwegian Institute of Public Health.

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Every year, more than 9000 Norwegians suffer a hip fracture. A decline in age-specific incidence has been observed. However, fracture burden is projected to increase due to an ageing population. The current project is organized into three work packages (WPs), intended to give novel and comprehensive information on an old public health problem that has long remained unresolved. We will use our national database of hip fractures (NORHip) in combination with health studies and registers covering the entire Norwegian population. New methodological approaches will be applied. In WP1 we develope a pioneer model (named Hip-IMPACT) for estimating the contribution of changes in risk factors and treatments to explain the decline in hip fracture incidence. In collaboration with the University of Liverpool this is a further development of their IMPACT model originally developed for cardiovascular disease mortality. The basis for WP2 is the connection between immune function and bone metabolism. However, it has been unsettled if variation in immune function in the general population affects the risk of fracture. We are utilizing the unique possibility to study long-term risk of osteoporosis and hip fracture across the range of immune responses assessed by the tuberculin skin test in a very large population-wide cohort. As a spinoff, we are also studying the association between immune response and osteoarthritis of the hip. In WP3 we combine already available data on day-to-day weather conditions, climate changes, topography and air pollution with individual-level socio-demographic and fracture outcome data integrated in a Geographic Information System (GIS). This will enable us to quantify the influence of these environmental factors on fracture incidence across Norway. The research is conducted by NOREPOS, a longstanding national research network comprising the four medical faculties in Norway and the Norwegian Institute of Public Health.