Night-shift work, sleep duration, daytime napping, and breast cancer risk.

Sleep habits vary among different countries, and sleep problems may cause various health problems. The aim of our study was to evaluate the separate and combined associations of night-shift work, sleep duration, and daytime napping with breast cancer risk among the Chinese population. This study conducted face-to-face interviews with 712 women diagnosed with incident invasive breast cancer before treatment and 742 age-matched controls. Information on sleep habits, demographic characteristics, and suspected or established risk factors of breast cancer were collected from the two groups. Multivariate logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs). Night-shift work was associated with an increased risk of breast cancer [OR (95% CI): 1.34 (1.05-1.72)]. Compared to women with a sleep duration of 6.1-8.9 h/day, women who had shorter [(≤6.0 h/day) (OR (95% CI): 1.53 (1.10-2.12)] and longer (≥9.0 h/day) sleep duration [(OR (95% CI): 1.59 (1.17-2.17)] had an increased risk of breast cancer. In addition, daytime napping was associated with a reduced risk of breast cancer among night-shift workers [OR (95% CI): 0.57 (0.36-0.90)], but no association was found among women who never had night-shift work [OR (95% CI): 1.01 (0.75-1.35)] (P for interaction = 0.054). Night-shift work and longer sleep duration also synergistically increased breast cancer risk [OR (95% CI): 3.69 (1.94-7.02)] (P for interaction = 0.009). Sleep problems, including night-shift work, and shorter and longer sleep duration, are associated with an increased breast cancer risk. In particular, the combined effects of night-shift work with no daytime napping or longer sleep duration are greater than the independent effects.

Wang P ，Ren FM ，Lin Y ，Su FX ，Jia WH ，Su XF ，Tang LY ，Ren ZF ... -  《-》

Association of shift-work, daytime napping, and nighttime sleep with cancer incidence and cancer-caused mortality in Dongfeng-tongji cohort study.

Bai Y ，Li X ，Wang K ，Chen S ，Wang S ，Chen Z ，Wu X ，Fu W ，Wei S ，Yuan J ，Yao P ，Miao X ，Zhang X ，He M ，Yang H ，Wu T ，Guo H ... -  《-》

Nested case-control study of night shift work and breast cancer risk among women in the Danish military.

Hansen J ，Lassen CF 《-》

Case-control study of shift-work and breast cancer risk in Danish nurses: impact of shift systems.

Working outside normal daytime hours is increasing worldwide and is now one of the most widespread potential carcinogenic occupational exposures. There is sufficient evidence in experimental animals that light exposure during the biologic night increases tumour growth and limited epidemiologic evidence that night shift-work cause breast cancer. Existing studies had crude definitions of shift-work and did not discriminate between shift-work systems (e.g. permanent versus rotating or evening versus night). We performed an interview based nested case-control study within a nationwide cohort of Danish nurses, including detailed information on lifetime shift-work and potential confounders. Cases of primary breast cancer (n=310) were identified from the nationwide Danish Cancer Registry. Four control nurses were selected for each case by incidence density sampling. Odds rations (ORs) and 95% confidence intervals (CIs) were estimated by conditional logistic regression, with adjustment for potential confounders. Overall, nurses who worked rotating shifts after midnight had a significantly increased OR (1.8; CI 1.2-2.8) for breast cancer compared to nurses with permanent day work. No association was found in a small group of nurses with evening work and no night work (OR=0.9; 0.4-1.9). The subgroup of nurses with periods of permanent night shift in addition to rotating night and day shifts experienced an OR of 2.9 (1.1-8.0). For nurses working after midnight compared to nurses never ending work before midnight, OR in the third tertile of cumulative number of shifts was 2.2 (1.5-3.2). In an analysis of different rotating shift systems, the highest OR (2.6; 1.8-3.8) was observed for long-term day-night rotating shifts. The results provide further evidence that night shift-work may increase the risk for breast cancer and suggest that the largest impact on risk is associated with the most disruptive shifts. Danish Cancer Society and National Programme of Environmental Health Research.

Hansen J ，Stevens RG 《-》

Breast cancer risk and night shift work in a case-control study in a Spanish population.

Papantoniou K ，Castaño-Vinyals G ，Espinosa A ，Aragonés N ，Pérez-Gómez B ，Ardanaz E ，Altzibar JM ，Sanchez VM ，Gómez-Acebo I ，Llorca J ，Muñoz D ，Tardón A ，Peiró R ，Marcos-Gragera R ，Pollan M ，Kogevinas M ... -  《-》