[1] Mayo Clin & Mayo Fdn, Div Epidemiol, Dept Hlth Sci Res, Rochester, MN 55905 USA
[2] Dartmouth Coll, Hitchcock Med Ctr, Dartmouth Med Sch, Ctr Evaluat Clin Sci, Hanover, NH 03756 USA
[3] Malmo Gen Hosp, Dept Orthopaed, S-21401 Malmo, Sweden
[4] Univ Sheffield, WHO, Collaborating Ctr Metab Bone Dis, Sch Med, Sheffield, S Yorkshire, England