Experimental and epidemiologic studies suggest that light at night (LAN) exposure disrupts circadian rhythm, and this disruption may increase breast cancer risk. We investigated the potential association between residential outdoor LAN and breast cancer risk. A population-based case–control study was conducted in Vancouver, British Columbia and Kingston, Ontario, Canada with incident breast cancer cases, and controls frequency matched by age in the same region. This analysis was restricted to 844 cases and 905 controls who provided lifetime residential histories. Using time-weighted average duration at each home 5–20 years prior to study entry, two measures of cumulative average outdoor LAN were calculated using two satellite data sources. Logistic regression was used to estimate the relationship between outdoor LAN and breast cancer risk, considering interactions for menopausal status and night shift work. We found no association between residential outdoor LAN and breast cancer for either measure of LAN [OR comparing highest vs. lowest tertile (DNB) = 0.95, 95% CI 0.70–1.27]. We also found no association when considering interactions for menopausal status and past/current night work status. These findings were robust to changes to years of residential data considered, residential mobility, and longer exposure windows. Our findings are consistent with studies reporting that outdoor LAN has a small effect or no effect on breast cancer risk.

实验和流行病学研究表明，夜间（LAN）暴露会破坏昼夜节律，这种破坏可能会增加患乳腺癌的风险。我们调查了居民室外局域网与乳腺癌风险之间的潜在关联。在加拿大不列颠哥伦比亚省的温哥华和加拿大安大略省的金斯敦进行了一项基于人群的病例对照研究，研究对象是乳腺癌病例，并根据同一地区的年龄对对照频率进行控制。该分析仅限于提供终生居住历史的844例病例和905例对照。使用进入研究前5-20年的每个家庭的时间加权平均持续时间，使用两个卫星数据源计算了两个累积平均室外LAN的度量。使用Logistic回归估计室外LAN与乳腺癌风险之间的关系，考虑更年期状态和夜班工作的相互作用。我们发现，无论哪种局域网测量，住宅室外局域网与乳腺癌之间都没有关联[或比较最高三分位数与最低三分位数（DNB）= 0.95，95％CI 0.70–1.27]。在考虑更年期状态和过去/当前夜间工作状态的交互时，我们也没有发现任何关联。这些发现对于考虑多年的住宅数据变化，住宅流动性和更长的暴露时间是有力的。我们的发现与报告户外LAN对乳腺癌风险影响很小或没有影响的研究一致。在考虑更年期状态和过去/当前夜间工作状态的交互时，我们也没有发现任何关联。这些发现对于考虑多年的住宅数据变化，住宅流动性和更长的暴露时间是有力的。我们的发现与报告户外LAN对乳腺癌风险影响很小或没有影响的研究一致。在考虑更年期状态和过去/当前夜间工作状态的交互时，我们也没有发现任何关联。这些发现对于考虑多年的住宅数据变化，住宅流动性和更长的暴露时间是有力的。我们的发现与报告户外LAN对乳腺癌风险影响很小或没有影响的研究一致。