Quality of municipal drinking water and the risk of osteoporotic fractures in Norway

Background: For mainly unknown reasons, the Norwegian population has among the highest incidence rates of osteoporotic fractures in the world. The risk of fracture has been shown to vary within Norway, with higher risks in the urban compared to rural areas. Norwegian drinking water is distinct; it contains less minerals and is more corrosive towards water pipes compared to water in many other countries. Drinking water quality has generally improved in recent years, but the quality still differs across Norway. The overall aim of this thesis was to examine whether the variations in quality of drinking water could be related to the risk of osteoporotic fractures, such as fractures of the hip and the forearm. Methods: To link area information on water quality to individual fracture outcomes, a map of the waterworks supply-areas was produced using Geographic Information Systems. Water quality information was provided by the Norwegian Waterworks Register and by a survey of trace metals in water, whereas fracture information came from the Cohort of Norway (CONOR) collection of health surveys and a recently established database of hip fractures named “NORHip”. Using logistic regression, variations in risk of self-reported forearm-fracture in CONOR were assessed between groups of varying water-acidity (pH). Differences in incidence of hip fractures in NORHip by levels of calcium, magnesium and three toxic metals (cadmium, lead and aluminum) were evaluated by Poisson-regression. Available background information, along with other water quality factors were taken into account, testing for confounding, mediation, effect modification and interaction. Main Results: The risk of forearm fracture was found to be higher when the water was slightly acidic (pH