Night Shift Work May Cause Cancer
Studies Suggest Link Between Circadian Rhythm Disruption and Cancer
Nov. 30, 2007 -- Working the night shift may cause cancer, according to a report
published in The Lancet.
The report comes from a team of 44 scientists in 10 countries commissioned
by the World Health Organization's International Agency on Cancer Research.
They report "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.
But those studies, which were observational, don't prove cause and
effect. Many genetic and environmental factors affect cancer risk.
So the scientists also reviewed studies in which animals were exposed to
light at night, disrupting the animals' so-called body clocks (circadian
Those studies provided "sufficient evidence" of a connection between
circadian rhythm disruption and cancer, states the report.
The scientists concluded that "shift work that involves circadian rhythm
disruption is probably carcinogenic to humans," write Kurt Straif, MD, and
They note that shift work may raise cancer risk by suppressing production of
melatonin, a chemical involved in the circadian
Straif works in Lyon, France, for IARC.
The scientists also concluded working as a painter is carcinogenic and that
working as a firefighter is "possibly carcinogenic" due to on-the-job