Is there a clear link between shift work and breast cancer?
A 2008 review found only limited evidence. Yet there was enough data to convince the International Agency for Research on Cancer.
The IARC convened a working group in 2007. It was composed of 24 scientists from 10 countries. The experts reviewed all of the research.
They concluded that working night shifts is “probably carcinogenic to humans.” This means that shift work may be a factor “that can increase the risk of human cancer.”
The report was the basis for the Danish government’s compensation program. So far almost 40 women have received payment through the program.
How might night shifts promote breast cancer?
The exact mechanism is unclear. But it may be related to how shift work disrupts the “circadian rhythms” that are controlled by the body clock in your brain. This internal timing system regulates the daily cycle of various body functions.
It controls your body temperature and hormone levels. It also regulates your alertness.
One way the body promotes sleepiness is by producing more melatonin at night. This acts as a “sleep signal” for your body.
But light exposure during night shifts suppresses melatonin production and disrupts your sleep/wake cycle. These disruptions may promote the growth of cancerous tumors.
Get sleep tips for shift workers from the AASM.