Quality of municipal drinking water and the risk of osteoporotic fractures in Norway
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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<7). However, including possible intermediate factors, such as microbial indicators, showed that these could be of more importance than acidity in itself for fracture prediction. A higher magnesium concentration in the water was found to have a protective association with hip fracture, but the results for calcium were inconclusive. Although the concentration of toxic metals in the water was generally low, men seemed to be at higher risk of hip fracture with a slightly higher level of cadmium in water. An increased risk for hip fracture in the oldest men and women (66-85 years) was also found with higher concentrations of the toxic metal lead in water. Interaction analyses indicated that collective effects of toxic metals may be stronger than singular effects. Conclusion: Due to few studies on drinking water quality and bone health, the current thesis needs to be considered exploratory. Nevertheless, our results suggest that increasing the concentration of magnesium in drinking water could be an important protective measure against osteoporotic fractures in the population. Also, ensuring that the water is free of possible disease-causing organisms, and reducing the concentration of toxic metals such as lead and cadmium may be of benefit to bone health.
Has partsPaper I: Dahl, C., et al., Is the quality of drinking water a risk factor for self-reported forearm fractures? Cohort of Norway. Osteoporos Int, 2013. 24(2): p. 541-51. The article is not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1007/s00198-012-1989-7
Paper II: Dahl, C., et al., Nationwide data on municipal drinking water and hip fracture: Could calcium and magnesium be protective? A NOREPOS study. Bone, 2013. 57(1): p. 84-91. The article is not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1016/j.bone.2013.06.017
Paper III: Dahl, C., et al., Do Cadmium, Lead, and Aluminum in Drinking Water Increase the Risk of Hip Fractures? A NOREPOS Study. Biol Trace Elem Res, 2013. 157(1): p. 14-23. The article is not available in BORA due to publisher restrictions. The published version is available at: http://dx.doi.org/10.1007/s12011-013-9862-x