Eva Schernhammer and her colleagues at the Harvard School of Medicine in 2001, using data collected from the 78,562 women in the Nurses' Health Study, reported an association between night work and breast cancer. In their analysis, they found that for women who had worked 30 years or more on rotating night shifts had a 36% increased risk of breast cancer. In 2003 Schernhammer et al reported another finding in the risk for colorectal cancer and night shift workers. They found that those who had worked more than 15 years of night shifts had a 44% increased risk of developing colorectal cancer. Other studies have linked night shift work with increased risk for other malignancies, including endometrial, prostate and non-Hodgkin’s lymphoma. In addition, working night shifts has also been associated with increased risk of chronic non-malignant disease, such as gastrointestinal disorders, cardiovascular disease, stroke, and diabetes.
 
Is working night shift all bad for our health? In 2006, Chen et al reported that nurses who had worked 15 or more years on rotating night shifts had half the risk of developing Parkinson’s disease as nurses who had never worked night shifts. The nurses who slept longer than 9 or more hours and those who slept 6 hours or less per day had an 84% increase in risk of developing Parkinson’s disease.
 
In addition, Schernhammer et al just published another retrospective statistical analysis of data collected from 68,336 women in the Nurses’ Health Study on the relationship between working rotating night shifts and skin cancer. Interestingly enough, the results are not what we would have predicted. This study found that for women working 10 years or more on rotating night shifts were associated with a 44% decreased risk of melanoma. The simplest explanation for the association between night-shift work and decreased skin cancer risk would be lack of sun exposure; however, the author ruled out this possibility as there were no geographical variations in their results.
 
In summary, women who had worked 30 years or more on rotating night shifts had a 36% increased risk of breast cancer, those who had worked more than 15 years of night shifts had a 44% increased risk of developing colorectal cancer, nurses who had worked 15 or more years on rotating night shifts had half the risk of developing Parkinson’s disease and women who had worked 10 years or more on rotating night shifts were associated with a 44% decreased risk of melanoma. The results of all the studies suggest that the role melatonin plays in the circadian disruption may be more complex than we previously thought.
 
Reference
Schor, J. Night Shift Work Decreases Risk of Melanoma. Natural Medicine Journal. October 2011 vol. 3 Issue 10.