But study didn't prove cause-and-effect relationship
FRIDAY, March 15 (HealthDay News) -- Working at night might do more than throw your schedule out of whack, researchers warn. Women who cover the night shift may be at increased risk for ovarian cancer, according to a new study.
The investigators also found that the risk of ovarian cancer may be lower for night types ("owls") than for morning types ("larks").
The study included more than 1,100 women with the most common type of advanced ovarian cancer, including about 390 with borderline disease, and more than 1,800 women without ovarian cancer. The women were aged 35 to 74, and worked in fields including health care, food service and office administration.
Nearly 27 percent of the women with invasive cancer had worked nights, compared with about 32 percent of those with borderline disease and about 22 percent of those without ovarian cancer, the findings showed.
Working night shifts was associated with a 24 percent increased risk of advanced cancer and a 49 percent increased risk of early stage cancer, according to the study, which was released March 14 in the journal Occupational and Environmental Medicine.
Only women 50 and older were significantly more likely to have ovarian cancer if they had worked nights, study author Parveen Bhatti, of the Fred Hutchinson Cancer Research Center in Seattle, said in a journal news release.
Of the women in the study who had worked night shifts, 27 percent said they tended to be night owls and 20 percent said they were morning larks. The risk of advanced ovarian cancer was higher among larks than among owls (29 percent versus 14 percent), as was the risk of borderline disease (57 percent versus 43 percent).
The researchers suggested that the increased cancer risk in women who work night shifts could be associated with the hormone melatonin, which regulates reproductive hormones, particularly estrogen. Melatonin is normally produced at night but is suppressed by light.
Previous research has suggested that night-shift work may be associated with an increased risk of breast cancer.
Although the study found an association between night-shift work and increased risk of ovarian cancer, it did not prove a cause-and-effect relationship.
The American Cancer Society outlines the risk factors for ovarian cancer (http://www.cancer.org/cancer/ovariancancer/detailedguide/ovarian-cancer-risk-factors ).
SOURCE: Occupational and Environmental Medicine, news release, March 14, 2013