Physical activity, sedentary time and breast cancer risk: a Mendelian randomisation study by Dixon-Suen, SC, Lewis, SJ, Martin, RM, English, DR, Boyle, T, Giles, GG, Michailidou, K, Bolla, MK, Wang, Q, Dennis, J, Lush, M, Ahearn, TU, Ambrosone, CB, Andrulis, IL, Anton-Culver, H, Arndt, V, Aronson, KJ, Augustinsson, A, Auvinen, P, Beane Freeman, LE, Becher, H, Beckmann, MW, Behrens, S, Bermisheva, M, Blomqvist, C, Bogdanova, NV, Bojesen, SE, Bonanni, B, Brenner, H, Brüning, T, Buys, SS, Camp, NJ, Campa, D, Canzian, F, Castelao, JE, Cessna, MH, Chang-Claude, J, Chanock, SJ, Clarke, CL, Conroy, DM, Couch, FJ, Cox, A, Cross, SS, Czene, K, Daly, MB, Devilee, P, Dörk, T, Dwek, M, Eccles, DM, Hunter, DJ