Burning the Midnight Oil: Night Shift Work May Increase Cancer Risk

Research constantly highlights how adequate sleep impacts health outcomes. A recent meta-analysis, published in Cancer Epidemiology, Biomarkers & Prevention, delved in a bit further to see if people who stayed up all night for work had an increased chance of developing cancer.

Researchers looked at 61 studies conducted throughout Europe, North America, Asia and Australia that included more than 3.9 million women whose careers required them to work night shifts.

The strongest correlation was seen with breast cancer — for every five years a woman worked the night shift, her breast cancer risk increased by 3.3 percent. This population was also discovered to have an increased risk of digestive system cancer and skin cancer. Interestingly, nurses who worked night shifts also had a higher incidence of lung cancer.

“It is usually considered that night shift work impairs health, but we were still surprised by the increased risks attributed to long-term night shift work when we integrated the statistics together,” study author Xueli Ma, assistant professor at West China Hospital, Sichuan University, said in an interview with CURE.

Ma noted that previous studies have found possible reasons why night shift work can be so bad for an individual’s health. First, circadian rhythm disruption, which typically happens with nocturnal melatonin suppression, can act as a carcinogen. Since melatonin plays a role in preventing tumor growth through antioxidation, antiangiogenisis and immunity regulation, reducing natural melatonin release — which is an effect of being exposed to artificial light during the night time – can promote cancer growth.

Another explanation also focuses on circadian rhythm. When someone disturbs that rhythm, it results in changes of clock gene expression, making them more prone to cancer. And while the researchers could not measure patients’ other lifestyle factors, they do believe that cancer growth could be multifaceted.

“The occurrence and development of the tumor is the result of environmental and biological factors in combination,” Ma said. “In addition to the hormone level, previous researchers supposed that some alterations in one’s lifestyle, like dietary factors, lack of physical activity and disordered sleep might also contribute to the increased risk of cancer.”

Ma mentioned that there are some steps that could be taken to improve health in this population.

“We need a more scientific duty system, requiring more staff input and scientific management,” he said, noting that it is important to have a good quality of life by staying active and maintaining a healthy diet. Melatonin supplementation may be able to help, too, Ma said, though more trials need to be conducted to support that.

Also, Ma pushed for a better tumor-specific screening strategy, especially for those who are high risk — like female night shift workers who may be more prone to breast cancer.

Most importantly, more studies also need to be done to continue finding ways to improve health and prevent cancer in people who work night shifts.

“Night shift work is inevitable responding to social development, this it is quite necessary to alleviate the problem practically and properly,” Ma said.