Long-term nightshift work and breast cancer risk
Night shift work may disturb circadian rhythms. While this disturbance could influence the risk of breast cancer, research papers have reported conflicting results. A group of mainly Spanish researchers reviewed, summarized, and combined the results of studies measuring the effect of long-term nightshift work (15 years or more) on breast cancer with special attention to menopausal status and time since retirement age. After discarding many studies where there may have been a risk of bias, they considered 18 studies.
They found that women with long-term night shift work had 13 per cent more risk of breast cancer than women who did not do night shift work. Postmenopausal women showed no increased risk, while premenopausal women had a 27 per cent higher risk. Women with a higher probability of recent long-term night shift work (women under retirement age) had a 23 per cent higher risk than women who did not work such shifts.
The researchers concluded that long-term night shift work may increase the risk of breast cancer, especially in women before menopause or shortly after discontinuation of nightshift work.
Read more: Schwarz, C, et al, Long-term nightshift work and breast cancer risk: An updated systematic review and meta-analysis with special attention to menopausal status and to recent nightshift work [Creative Commons Open access: MDPI Summary or full text] Cancers (Basel), vol.13 (2021), no. 23.
Night work, rotating shift work, and the risk of cancer in Japanese men and women
In another study looking at the effects of shift work, and the limited evidence linking it to various cancers, Japanese researchers investigated whether there is an association between different forms of work schedule and the risk of numerous cancers among Japanese men and women.
The study cohort was 45,390 working men and women aged 40–79 years and registered in the Japan Collaborative Cohort Study (JACC Study) to calculate the hazard ratios for cancer among those who working night work and rotating shift work for their longest occupations compared with day work.
They found that among men, rotating shift work was significantly associated with increased risk of esophageal cancer, and also found that it tended to be associated with the increased risk of prostate cancer.
Read more: Arafa, A, et al Night Work, Rotating Shift Work, and the Risk of Cancer in Japanese Men and Women: The JACC Study. [Creative Commons Open access: Abstract or pdf of Full study] Journal of Epidemiology, Volume 31 (2021) Issue 12