Breast cancer risk and epigenetic effects of the rotating night shift work and lifestyle.

Norwegian case-control study

A cohort of 49,402 female nurses who graduated from a 3-year nursing school between 1914 and 1985 was established in 2004, based on information from the Norwegian Board of Health’s registry of nurses. An interview-based case-control study of 1182 women aged 35-74 years was nested within this cohort (for details see Lie et al 2011). The cases (n=563) were all women diagnosed with histologically confirmed invasive breast cancer between 1990 and 2007, alive in February 2009, who consented to be interviewed, and had an occupational history as a nurse of at least one year. The control subjects (n=619) were frequency matched to cases on year of diagnosis and 5-year age-groups. DNA was isolated from saliva samples provided by the participanting nurses.