Earlier research in animals had suggested that disturbances in the light-dark cycle could knock certain chemicals in the body, melatonin and estrogen off balance, and as a result increase cancer risk.
- The WHO International Agency for Research on Cancer had concluded that night-shift work was a probable cause of cancer.
- U.K. Health and Safety Executive issued a report estimating that almost 2,000 British women get breast cancer every year due to shift work.
- A Chinese study however showed no sign of a connection between night-shift work and breast cancer.
Does working nights cause breast cancer?