In research that echoes previous studies about the increase of diseases in those who work overnight, new research has drawn a strong correlation between ovarian cancer and an inverted work schedule.

By tracking the health of 3,000 women who worked night shifts, researchers found that they had an increased rate of early stage ovarian cancer by nearly 50 percent compared to women who worked a regular day shift.

Researchers speculate that a possible imbalance caused by the disruption of the sleep hormone melatonin may be a leading factor. 

In the current research, investigators examined 11,100 cases of women with ovarian cancer, 389 cases of women with borderline disease and 1,832 women who were not ill. They found that roughly one in four women with advanced cancer worked the night shift, with one third of borderline cancer working overnight and only one in five in the control group working overnight.

After computing the data it was seen that there was a 24 percent increase in risk of ovarian cancer and a 49 percent increase in the risk of early stage cancer for women who worked through the night.  These women on average had worked for two to three years health care, food preparation and service, office and administrative support.

Data in this study indicates that women who work the night shift do have fewer children than their diurnal counterparts. There is evidence that childbearing does reduce the risk of ovarian cancer.

Similar findings published in 2001 and 2012 looked at the rates of breast cancer in women who worked overnight either as medical professionals or in the military.   They found a dose dependence where women who worked overnight military shifts longer had a higher incidence of breast cancer. Researchers also found that women who preferred nights as opposed to days had a less likely risk of breast cancer. This finding was not seen in the present analysis of ovarian cancer. 

The current research was published in the journal Occupational and Environmental Medicine and can be found here