A report published in The Lancet appears to question whether working the night shift is a good idea. The report comes from several dozen scientists in 10 countries commissioned by the World Health Organization's International Agency on Cancer Research to investigate the idea that breaking one's circadian rhythm could cause cancer.
The report shows "limited" evidence of a connection between cancer and night shift work in people. That evidence included a higher rate of breast cancer in female nurses who work night shifts. While the studies of nurses were purely observational, and didn't prove cause and effect, the scientists also reviewed animal studies.
In this case, animals were exposed to light at night, disrupting the animals' so-called body clocks, or their circadian rhythm. In this case, those studies provided "sufficient evidence" of a connection between circadian rhythm disruption and cancer. This is concerning.
The scientists concluded "shift work that involves circadian rhythm disruption is probably carcinogenic to humans." One of the co-authors speculated that shift work may raise cancer risk by suppressing production of melatonin, a chemical involved in circadian rhythm.