Impact of road traffic noise on obesity measures: observational study of three European cohorts by Cai, Y, Zijlema, WL, Sørgjerd, EP, Doiron, D, de Hoogh, K, Hodgson, S, Wolffenbuttel, B, Gulliver, J, Hansell, AL, Nieuwenhuijsen, M, Rahimi, K, Kvaløy, K