[1] Childrens Hosp Eastern Ontario, Res Inst, Hlth Act Living & Obes Res Grp, Ottawa, ON K1H 8L1, Canada
[2] Hosp Sick Children, Physiol & Expt Med Program, Toronto, ON M5G 1X8, Canada
[3] STAT Canada, Hlth Anal Div, Ottawa, ON, Canada
[4] CDC, Natl Ctr Environm Hlth, Atlanta, GA 30333 USA