The effects of shift work and sleep duration on cancer incidence in Alberta`s Tomorrow Project cohort

We investigated the main effects of shift work and sleep duration on cancer incidence, and effect modification of the shift work-cancer incidence association by sleep duration.

Shift work and sleep duration were assessed among 21,804 participants from Alberta`s Tomorrow Project. Incident cases of breast, prostate, colorectal and lung cancers were identified through registry linkage.

Having worked ≥6 years of rotating shift work (HR = 1.59, 95 % CI = 1.07, 2.37; P = 0.02) and having ever worked night shifts were associated with an increased risk of lung cancer (HR=1.71, 95 % CI=1.18, 2.47; P = 0.01), whereas having ever worked night shifts was associated with a reduced risk of prostate cancer in the latency-adjusted model only (HR=0.70, 95 % CI=0.51, 0.98; P = 0.04). No associations were found between shift work or sleep duration on the risks of breast and colorectal cancers. Some evidence of effect modification by sleep duration for the rotating shift work-lung cancer incidence association was noted (P = 0.06), with stratified analyses revealing borderline increased risk of lung cancer in participants with ≥6 years of rotating shift work and <7 h of sleep/day (HR=2.27, 95 % CI=0.95, 5.41; P = 0.07), and an increased risk of lung cancer in participants with 0.1-5.9 years of rotating shift work and >9 h of sleep/day (HR=2.99, 95 % CI=1.12, 7.97; P = 0.03). No additional evidence of effect modification by sleep duration for shift work and cancer incidence was noted.

A consistent association between shift work employment and lung cancer risk was noted in this Canadian sample. Furthermore, some evidence of effect modification of the rotating shift work-lung cancer risk association by sleep duration was noted.