[1] Univ Manitoba, Dept Med, Winnipeg, MB, Canada
[2] Columbia Univ, Dept Med, New York, NY USA
[3] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[4] Univ Sheffield, WHO Collaborating Ctr Metab Bone Dis, Sheffield, S Yorkshire, England