Working the night shift tied to breast cancer risk

Disruption in melatonin levels, circadian rhythm can increase risk four fold

Women who work the night shift at least three nights a week might be at a 40% greater risk of developing breast cancer, according to a study conducted by the Danish Cancer Society.

The risk doubled among women who worked three nights a week for over six years, and quadrupled among those that considered themselves morning people as opposed to night people.  

 “Night shift work involves exposure to light at night, which decreases the production of the night hormone melatonin that seems to protect against certain cancers,” says research leader Dr. Johnni Hansen.

The night shift also disrupts the body’s circadian rhythm, causing the brain’s natural clock to desynchronize with the cellular clocks in different organs. Moreover, sleep deprivation after a night shift suppresses the immune system, which can increase the risk of cancer cell growth.

Between 10% and 20% of women currently work a night shift. With that in mind, Dr. Hansen suggests, “this type of work should be limited in duration and limited to less than three shifts per week… In particular, morning types should limit their night work.”

The study included over 18,500 women between 1964 to 1999. Researchers surveyed 210 women that contracted breast cancer and 899 women that did not.

Reduce the risks at work and at home
Because certain wavelengths suppress melatonin more than others, workplaces can adjust the lighting in their facilities to eliminate these wavelengths, says Richard Stevens of the UConn Health Center.

According to Stevens, “if you wake up during the night, stay in the dark; don’t turn on the light" because it starts suppressing melatonin immediately.

While there is an association between working the night shift and increased breast cancer incidence, researchers reiterated that there are numerous environmental and genetic factors that actually cause the disease. Researchers are further investigating the association between night work and prostate cancer (Reinberg, HealthDay, 5/29; United Press International, 5/29)


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