Results
0verall, the authors observed an adjusted 0R of .1.4 (95% Cl 0.9 to 2.1)among women with ever compared with never night shifts. The RR for breast
cancer tended to increase with increasing number of years of night shift work
(p=0.03) and with cumulative number of shift (p=0.02),with a neutral risk for fewer than three night shifts per week. The OR for the group with the highest tertile of cumulative exposure was 2..3 (95% Cl 1.2 to 4.6). The most pronounced effect of night shift work on breast cancer risk was observed in women with morning chronotype preference and intense night shifts (OR=3.9, 95% Cl 1.6 to 9.5). Night shift workers tended to sunbathe more frequently than day workers.