According to a Harvard University and Brigham and Women’s Hospital study, women who regularly work at night may have as much as a 50% increased risk of breast cancer.
The study suggests it cause may be due to their greater exposure to artificial light, which increases the female hormone estrogen.
Harvard doctors analyzed data on more than 10,000 women, including several hundred airline cabin staff, and determined that night workers were 1.5 times more likely to get cancer than those who worked during the day.
The results of the study appear in the European Journal of Cancer and are supported by earlier research connecting cancer to sleeping with the light on and suggesting the negative impact of night shifts and frequently fluctuating between day and night shifts.
The likely explanation for the increased cancer risk involves the hormones melatonin and estrogen. Melatonin is normally released into the body at night to regulate sleep patterns.
Maintaining normal melatonin levels at night has been shown to be beneficial. In previous research women with high levels of melatonin in the morning were found to be at lower risk of breast cancer.
When working night shifts interferes with normal melatonin “possibly through exposure to artificial light " the ovaries produce more estrogen. This excess of estrogen can cause the development of breast tumors.
Currently many businesses, including call centers, tech-support services as well as the retail, entertainment, and fast-food industries require the employment of millions of night shift workers.
Working nights has been shown to increases the risk of heart disease, depression, and other types of cancer and according to one study, is more damaging than smoking 20 cigarettes a day.