Reasons shift and night work can be harmful

Researchers are trying to establish why shift and night work would cause harm to workers. Read summaries of this research.

Impact of shift work on circadian rhythms

Humans evolved to fit into the environment which includes periods of light and darkness.  How we function in that dark-light cycle is down to a number of different physical processes called circadian rhythms. Our bodies release the hormone melatonin in the evening which results in tiredness.  Other circadian rhythms include our body temperature when humans are coldest between 3.00 am and 5.00 am.  There are a number of different circadian rhythms which help to manage different body functions.

Circadian rhythms are controlled in an area of the brain called the hypothalamus. Within the hypothalamus there is an area called the suprachiasmatic nucleus. The suprachiasmatic nucleus responds to light and through this controls our clock genes. While humans respond to internal messages from hormones, there is also the impact of external cues such as light influencing our circadian rhythms. When you think about travelling over time zones, changes in time and light cause us to have jetlag.

When we ask workers to work evenings and overnight this has an immediate impact on our levels of tiredness and our circadian rhythms.  For those working at night work for many years, other health impacts have also been identified.

Links between breast cancer and shift work

Most of the research to now has focused on breast cancer where a number of pathways for the disease to occur have been suggested.  These include the following:

• exposure to light at night reducing melatonin production, melatonin has anti-carcinogenic properties
• changes in the genes controlling circadian rhythms
• reduced exposure to Vitamin D due to lower exposure to sunlight for night workers.

While there is not a consistent answer to causation at this time, breast cancer is also linked to obesity.

Obesity and shift work—further research required

There is ongoing discussion in relation to obesity and shift work.

While we know that shift workers are more likely to be overweight, further research is needed to identify if that is down to intake, access to poor quality food or something as simple as eating at the wrong time of day in relation to our body clock.