Objective The majority of studies on night shift work and cancer have only involved women due to the focus on breast cancer. It has been suggested that mechanisms similar to those for breast cancer may occur for prostate cancer. However, only few studies have been reported for this cancer, which is the most frequent cancer in men.

Methods We conducted a nested case-control study within a historical cohort of 238.068 men employed in the Danish Military at the earliest in 1964 or later. Study subjects were obtained from the Supplementary Pension Fund database, including a unique personal ID provided to all residents in Denmark. We linked based on this ID with the files of the nationwide Danish Cancer Registry, and men aged less than 75 years old with first primary prostate cancer were retrieved for the period 1990 to 2003 (n=157). For each case, we randomly selected 10 cancer free controls frequency matched based on the age distribution of the cohort cases. Study subjects returned a structured questionnaire or were interviewed about their entire work history, including night work, diurnal preference and potential confounders, e.g. education and physical activity. We estimated odds ratios (RR) by logistic regression conditional on age.

Results The overall adjusted RR for prostate cancer after ever having night shifts was 1.3 (0.8–2.1). The RR for the subgroup with longest duration of night shifts (≥15 years) was 2.2 (1.1–3.4).

Conclusion We add further evidence to the association between night shift work and prostate cancer.