By Jimmy Downs

Monday Dec 24, 2012 (foodconsumer.org) -- Night shift jobs can increase the risk of developing breast cancer, studies have shown.  A new study published in International Journal of Cancer confirms the association between night work and risk of the breast cancer, particularly in young women.

The study led by F. Menegaux  from Inserm, CESP Center for research in Epidemiology and Population Health in Villejuif, France and colleagues shows that women who had engaged in night work for more than four years prior to having their full term pregnancy were almost twice as likely  as those who did not do night shift jobs to develop breast cancer.

Night shift jobs disrupt circadian rhythm and lead to the development of breast cancer, which is a known fact.  The current study carried out between 2005 and 2008 examined 1,232 cases of breast cancer and 1,317 population controls without the disease from a large population in France for their exposure to night shift jobs.

The study found 13 percent of breast cancer patients had ever worked on night shifts, compared to 11 percent among the controls, which means that those who worked night shifts were at 27 percent increased risk of breast cancer.

It was also found that women who worked on overnight shifts were 35 percent more likely to develop breast cancer and those who worked at night for 4.5 years or longer were 40 percent more likely to develop breast cancer.

Exposure to night work before the first full term pregnancy were at 95 percent increased risk of breast cancer.  Prior to the first full term pregnancy, mammary gland cells are not completely differentiated and more susceptible to circadian disruption effects, the authors say.

The researchers concluded "Our results support the hypothesis that night work plays a role in breast cancer, particularly in women who started working at night before first full-term pregnancy."