The known health impacts of shift and night work

Read about the health impacts of night work and shift work, the accidents and injuries that are associated with these forms of work, and who is affected.

Health impacts of shift work and night work

Cancers of the breast, colon, prostate, and rectum

The health impacts of night work have been identified and the International Agency for Research on Cancer (IARC) in 2020 classified night shift work as “probably carcinogenic to humans” for cancers of the breast, colon, prostate and rectum”.

Most of the research up to now has been on breast cancer. As well as an association with night work, there is increased risk of breast cancer when compared to workers who did not work nights. Where workers continued to work night shifts, their risk of cancer was increased by 5% for every five years worked.

Heart disease

Other health impacts from shift and night work include cardiovascular disease such as ischemic heart disease (narrowed heart arteries).  When comparing those working shifts with non-shift workers, an increased risk of 11% was found. Again, the risk increased the longer people worked night shifts (0.9%)

Stroke

Long working hours (over 40 hours per week) have also been linked to stroke. This link was found to increase risk by 33%. Levels of risk also increased as the number of hours worked increased.

Tiredness

Shift work, and especially night work, causes tiredness in people through disrupted sleep.

This is not helped by difficulty trying to sleep at the wrong time of day when others are awake. Often this results in reduced hours of sleep in those working nights. This has immediate impacts on how we function including inability to pay attention, memory lapses and irritability.

Obesity

Additionally shift work and night work have also been associated with being obese and overweight. A higher level of obesity has been found in those working permanent night shifts.

More research is needed to find out if this is due to poor eating habits, eating at the wrong time of day, or an additional impact of sleep disruption.

Accidents and injuries associated with shift work and night work

The link between workplace accidents and shift workers was identified in the early 1990s. More recent research has found that those who work afternoon shifts and night shifts are at an increased risk of an accident.

It is not only the time of the shift that is important but also the length of time between work shifts or the recovery time. One study has found that where individuals have to return more quickly to work in less than 11 hours, they are more likely to go to sleep at work, go to sleep while driving, injure themselves or injure others and harm equipment.