Introduction Night shift work may lead to sleep disorders and circadian rhythm disruption. It was classified as probably carcinogenic by IARC but, unlike breast or prostate cancer, there is only scant evidence of an association with lung cancer.

Objective To explore the role of night shift work and sleep disorders in lung cancer risk among women.

Methods Information on night work and sleep disorders over lifetime was obtained in a case-control study on female lung cancer in 716 cases and 758 population controls in the Paris area (WELCA). Logistic regression models adjusting for tobacco smoking and other relevant confounders were used to estimate odds ratios (OR) and 95% confidence intervals (CI) associated with night work exposure metrics (years of night work, frequency of night shifts), sleep duration per day (< 7 h, 7 h, ≥8 h) and sleep disorders (difficulty in falling asleep; waking up at night, too early or too tired; intake of sleep medicine). A sleep disruption index (SDI) was used to classify women by number of sleep disturbances in categories of low (0 or 1), medium (2 or 3) or high SDI (4 or 5).

Results The OR was 1.08 (95% CI 0.75–1.56) in women who ever worked at night. This OR did not increase with duration or frequency of night shifts. Women who slept 8 or more hours per day had an OR of 1.40 (95% CI 1.04–1.87) as compared to those who slept 7 hours. Women who had both high SDI and who worked at night for 6 or more years had an OR of 3.61 (95% CI: 1.27–10.23).

Conclusion Lung cancer risk among women was not associated with ever working at night in our study. The association with longer sleep duration is intriguing and warrants further scrutiny.