[1] Norrbotten Cty Council, OLIN Studies, SE-97189 Lulea, Sweden
[2] Umea Univ, Dept Publ Hlth & Clin Med, Div Med, SE-90185 Umea, Sweden
[3] Umea Univ, Dept Publ Hlth & Clin Med, Occupat & Environm Med, SE-90185 Umea, Sweden
[4] Univ Gothenburgh, Sahlgrenska Acad, Dept Internal Med, SE-40530 Gothenburg, Sweden