According to International scientists for the International Agency for Cancer Research, working night shifts may increase the risk of Breast and Colon cancer in women and prostrate cancer in men. The Disruption of regular sleep and circadian rhythms may reduce melatonin, a Hormone believed to inhibit the cell damage that causes cancer. According to Health Partners Research Foundation, 15-20% of the U.S and European work force are employed in Shift-work jobs.
Report of the IARC study; 3 Dec 2007