Another Cancer Linked to Night Shift Work

Ovarian cancer risks higher in women who have worked night shift hours

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) The body has a built-in time clock. When that clock is disrupted, problems can eventually arise. Working nights messes with the body’s clock and some women could be paying the price.

A new study suggests that women who work the night shift may have an increased risk of ovarian cancer.

Researchers found that just over 25 percent of the ovarian cancer survivors in the study had ever worked during night-time hours. The findings applied only to women aged 50 and over.

It should be noted, though, that ovarian cancer is rare, and the vast majority of women will never be impacted by the disease.

"Get 6 to 8 hours a sleep every night."

A study from Denmark found that working the night shift may increase a woman’s risk of obesity, diabetes and breast cancer.

The International Agency for Research on Cancer (IARC) has classified night work that interrupts the body’s clock, or circadian rhythm, as a risk factor for cancer. 

This study, which involved 3,300 women between the ages of 34 and 75, was led by Parveen Bhatti, PhD, MSc, BSc, assistant professor of epidemiology at the Fred Hutchinson Cancer Research Center in Seattle, Washington.

Participants included 1,101 women with advanced epithelial ovarian cancer, the most common form of the disease, and 389 women who had borderline disease. The study also had a comparison group of 1,832 women who did not have ovarian cancer.

The women were asked about their working history, including the hours they worked and if they had ever had night shifts.

Researchers found:

  • 293 (26.3 percent of 1,101) women with invasive ovarian cancer had worked nights at some point.
  • 125 (32.4 percent of 389) women with borderline disease that had worked night shifts.
  • 412 (22.5 percent of 1,832) of the women in the comparison group had worked at night.
  • Fewer women with invasive cancers had used birth control pills than women in the control group.
  • Those with invasive or borderline disease tended to have had fewer children than women with ovarian cancer.
  • Women with borderline disease were more likely to be younger than those with invasive disease.
  • Night work was associated with a 49 percent increased risk of early stage disease and a 24 percent higher risk of advanced cancer compared to women who worked during normal business hours.
  • The length of time a woman had worked the night shift did not impact her risks.
  • Only women 50 and older had significantly greater risks of ovarian cancer if they’d worked nighttime hours.

This year an estimated 22,000 women will be diagnosed with ovarian cancer. In other words, about one in 3,000 women will develop the disease.

So, the overall risk of developing ovarian cancer is very small. Increased risks, therefore, do not mean that the average woman is likely to have this disease, regardless of her work schedule.

The authors concluded that additional study is needed to confirm these findings.

This study was funded by the National Cancer Institute and published January 23 in the Occupational and Environmental Medicine. No competing interests were disclosed.

Reviewed by: 
Review Date: 
March 14, 2013
Last Updated:
August 16, 2013