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Am I at a greater risk of cancer if I do shift work?

The short answer is: maybe.

The International Agency for Research on Cancer (IARC) has concluded that shift work (working outside the normal workday, often at nighttime) probably causes cancer when it affects circadian rhythms (our internal clock). This conclusion is based on data from animal studies and a limited amount of research in humans.

Most research has looked at whether shift work increases the risk of breast cancer.

Researchers are not sure how shift work increases a person’s risk of getting cancer, but some possible explanations that are being studied are:

night shift worker on a railroad
  • Having sleep patterns disrupted can change the body’s natural rhythms or affect the production of chemicals.
  • Light exposure at night can decrease the amount of melatonin (a hormone) produced by the brain. Melatonin may slow tumour development or change the levels of other hormones, like estrogen.
  • Lifestyle risk factors, including smoking, drinking alcohol, an unhealthy diet, lack of exercise and an unhealthy weight, may be a result of shift work.
  • Lower exposure to daylight may decrease the body’s production of vitamin D or change the body’s production of hormones.

Phase shift may contribute to cancer due to changes at the cell and tissue level that result from working at unusual times. Some organs or cells within the body have a rhythmic process that is synchronized to the sleep-wake cycle. Phase shift happens when these rhythms become out of sync with sleep-wake rhythms.


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