Investigative Analysis

Melatonin Levels and the Graveyard Shift

March 2007

The most undesirable shift available for workers everywhere may have just gotten a little bit worse. Researchers from Harvard University, in a Nurse's Health Study of more than 78,000 subjects, believe that working even a few night shifts a month might increase your risk of colorectal cancer.

The higher risk is believed to be linked to low levels of melatonin, a hormone involved in regulating sleep. When under lab observation, melatonin acts as an inhibitor to tumors.

Melatonin levels reach their highest in the middle of the night for most people. They are so fragile that turning on the light can decrease the level by 10%. After just two weeks of intermittent light nightly, humans experience a rapid decline in melatonin production, according to Nurse's Health Study researchers.

This development is just the latest in a line of studies whose aims were to determine the role reduced melatonin levels play in a person's health.

A German study published in 2002 concluded, "since humans are exposed universally, even small risk elevations could lead to numerous cases." A study of 813 patients aged 20-74, conducted at the Fred Hutchinson Cancer Research Center in Seattle, Washington, discovered that "breast cancer risk was increased among subjects who frequently did not sleep during the period of night when melatonin levels were typically at their highest." Further, "there was an indication of increased risk among subjects with the brightest bedrooms. Graveyard shift work was associated with increased breast cancer risk…with a trend of increased risk with increasing years and with more hours per week of graveyard shift work."

Another study, this one conducted by the Department of Neurology at Jefferson Medical College in Philadelphia, PA, discovered "epidemiological observations of decreased breast cancer in blind women and increased breast cancer in women who do shift work." These sentiments were echoed by researchers in St. Petersburg, Russia, who discovered, "light deprivation inhibits the carcinogenesis"…observing an "increased risk of breast cancer in night shift workers, flight attendants, radio and telegraph operators and (a) decreased risk in blind women."

The Harvard study's co-author, Francine Laden of Boston's Brigham and Women's Hospital, does offer some encouragement for those presently working night shifts. She maintains that sleeping in as dark a room as possible during the day may counteract night-shift workers decline in melatonin production.

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