Scientists suspect that night shift work is dangerous because it disrupts the circadian rhythm, the body's biological clock. The hormone melatonin, which can suppress tumor development, is normally produced at night.
Light shuts down melatonin production, so people working in artificial light at night may have lower melatonin levels, which scientists think can raise their chances of developing cancer.
Sleep deprivation may also be a factor. People who work at night are not usually able to completely reverse their day and night cycles. "Night shift people tend to be day shift people who are trying to stay awake at night," said Mark Rea, director of the Light Research Center at Rensselaer Polytechnic Institute in New York, who is not connected to IARC or its expert panel.
Not getting enough sleep makes your immune system vulnerable to attack, and less able to fight off potentially cancerous cells.
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Confusing your body's natural rhythm can also lead to a breakdown of other essential tasks. "Timing is very important," Rea said. Certain processes like cell division and DNA repair happen at regular times.
But if the body needs to do something at an unusual time — like produce insulin in the middle of the night to help digest food — that can set off a chain reaction of biological mistakes.
