1. Downs S, Forastiere F, Forsberg B et al (2006) Air pollution and the risks to human health - Epidemiology. Available at: http://airnet.iras.uu.nl/ , University of Maastricht, Netherlands. Accessed November 15, 2006
2. Particulate matter air pollution: how it harms health (2005) Fact sheet EURO/04/05,World Health Organisation Europe. Berlin, Copenhagen, Rome. Available at: http://www.who.int/mediacentre/factsheets/fs187/en/ . Accessed November 15, 2006
3. World Health Organization (2006) WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide. Global update 2005. WHO Geneva, Switzerland. Available at: http://www.who.int/phe/air/aqg2006execsum.pdf . Accessed November 15, 2006
4. Meyer HE, Berntsen GK, Sogaard AJ et al (2004) Higher bone mineral density in rural compared with urban dwellers: the NOREPOS study. Am J Epidemiol 160:1039–1046
5. Sanders KM, Nicholson GC, Ugoni AM et al (2002) Fracture rates lower in rural than urban communities: the Geelong Osteoporosis Study. J Epidemiol Community Health 56:466–470