Worldwide Cancer Research: Can working night shifts cause cancer? (19 April 2022)

Summary

In a world where most people wake up with the sun and head to their ‘9 to 5’, night shift work can be a challenge – but can it also be bad for your health? What do those health effects mean for your risk of cancer? Can working night shifts cause cancer? Worldwide Cancer Research presents the evidence.

Content

In 2007, the International Agency for Research on Cancer (IARC) classified shift work that follows an irregular time pattern as a probable cause of cancer. This was based on some animal and human studies that found that people who worked shifts or during the night were more likely to develop some types of cancer, such as breast and prostate cancer.

It also came from the idea that not following the natural day/night cycle and disrupting that natural rhythm in your body, called your ‘circadian rhythm’, could have a negative impact on health. This is somewhat true, as there are biological processes that are triggered by exposure to daylight, or by hormones that fluctuate over the course of the day.

However, more recent studies on night shift work and cancer risk factor in information like this, such as BMI and waist size, and have not found that shift work itself makes someone more likely to cause cancer. In 2016, a meta-analysis (which combines the data of many different studies together) found no link between night shift work and breast cancer. In 2020, another meta-analysis that included data from 57 different studies and at least nine different types of cancer found no increased risk with night shift work.

So no, night shift work does not itself increase your risk of developing cancer. Instead, this type of working pattern may lead to other health behaviours or factors that increase your risk, such as being overweight or obese, or not doing enough physical activity.