<![CDATA[ Background:  Disruption of sleep patterns, and thereby the internal body clock, of shift workers directly influences their physiology and the rate of cancer development. Studies have shown that working night shifts three or more times per month elevates the risk of breast cancer in humans. Disrupted expression of circadian genes can alter breast biology and may promote cancer. This study aimed to examine the effects of circadian rhythm and environment factor on the risk of breast cancer in Kediri, East Java.Subjects and Method: This was a case-control study conducted in Kediri, East Java, from April to May 2018. A sample of 200 women was selected by fixed disease sampling. The dependent variable was breast cancer. The independent variables were work schedule, sleep duration, room light, room temperature, chemical exposure, and air pollution. The data were collected by questionnaire and analyzed by a multiple logistic regression.Results: Circadian rhythm and environment factor affected the risk of breast cancer. The risk of breast cancer increased with irregular shift work schedule (OR= 5.82; 95% CI= 2.26 to 14.95; p<0.001), sleep duration <5 hours (OR= 6.32; 95% CI= 2.59 to 15.39; p<0.001), room light (OR= 7.03; 95% CI= 2.39 to 20.65; p<0.001), warm room temperature (OR= 13.48; 95% CI= 5.26 to 34.53; p<0.001), air pollution (OR= 8.21; 95% CI= 3.19 to 21.11; p<0.001), and chemical exposure (OR= 2.90; 95% CI= 1.22 to 6.84; p= 0.015).Conclusion: The risk of breast cancer increased with irregular shift work schedule, sleep duration <5 hours, room light, warm room temperature, air pollution, and chemical exposure.Keywords: breast cancer, circadian rhythm, environment factorCorrespondence: Anindiya Ningtyas. Masters Program in Public Health, Universitas Sebelas Maret, Jl. Ir. Sutami No. 36 A, Surakarta 57126, Central Java. Email: Anindyaningtyas.an@gmail.com. Mobile: +6282232189898. Journal of Epidemiology and Public Health (2019), 4(1): 20-29https://doi.org/10.26911/jepublichealth.2019.04.01.03]]>
