Time for Cancer Risk

Every human body operates on a circadian rhythm—their 24-hour biological clock, which in large part is regulated by the hormone melatonin.  Shift work, short sleep duration, employment as a flight attendant, and exposure to light at night, all potential ways that adversely alter melatonin secretion to cause circadian disruption, have been found by some published studies to raise breast cancer risk.  Sara Wagner Robb, from the University of Georgia (Georgia, USA), and colleagues completed a meta-analysis of 28 published studies, 15 on shift work, 7 on short sleep duration, 3 on flight attendants, and 6 on light at night.  Data analysis suggested a significantly positive association between circadian disruption and breast cancer risk: relative risk was 1.19 for shift work, 1.120 for exposure to light at night, 1.56 for employment as a flight attendant, and 0.96 for short sleep duration.  A dose–response analysis showed that each 10-year increment of shift work was associated with 16 % higher risk of breast cancer risk. The study authors submit that: “Our meta-analysis demonstrates that circadian disruption is associated with an increased [breast cancer] risk in women.”