[1] Univ Massachusetts, Dept Gerontol, Boston, MA 02125 USA
[2] Northwestern Univ, Feinberg Sch Med, Dept Prevent Med, Chicago, IL 60611 USA
[3] Stanley Manne Childrens Res Inst, Mary Ann & J Milburn Smith Child Hlth Res Outreac, Chicago, IL USA
[4] Powdermill Nat Reserve, Carnegie Museum Nat Hist, Rector, PA USA
[5] Univ Illinois, Coll Appl Hlth Sci, Champaign, IL USA