Shift work and increased rates of cancer

Over the years there have been a number of reports suggesting a link between shift work and increased rates of cancer, in particular breast cancer in women.

One theory that has been proposed is that light at night supresses the production of the hormone melatonin which is known to have anti-carcinogenic properties. Potentially reducing the body’s ability to fight emerging cancer cells.

There are many types of shift pattern and there have been a number of studies looking at different shifts in different industries which have reached different conclusions. This variety makes it difficult to come to firm conclusions that can be applied across all industries.

Questions that arise include:

• If there is a link between shift work and cancer does the shift work cause the cancer or is some other factor at work?
• Is the risk the same for every type of worker or are some more susceptible?
• Are some types of work / shift patterns / industries a bigger risk than others? etc

The HSE’s Workplace Health Expert Committee (WHEC) recently published a paper reviewing the evidence for breast cancer and shift work. The WHEC found that the evidence on risks is complex and rapidly growing. The WHEC’s report aims to summarise the current state of knowledge and to place it in context for policy makers.

Over all the WHEC agrees, with the International Agency for Research on Cancer’s (a part of the World Health Organization) assessment that “a causal interpretation is considered credible, but chance, bias or confounding cannot be ruled out with reasonable confidence”.

When it comes to the question of whether certain groups are at particular risk the WHEC note that quite a lot of evidence suggests that risks are not increased for workers with less than 10 years night shift work and that increased risks are only observed to longer term exposure of 15 to 30+ years.

At this stage it looks like a simple solution is not practical and that further research will be required.

By identifying and assessing new and emerging issues in workplace health the WHEC provides independent expert opinion to HSE. As such while the expert opinions expressed by WHEC inform HSE policy they do not necessarily reflect HSE policy. The review report can be found on the HSE’s website at: https://webcommunities.hse.gov.uk/connect.ti/WHEC/view?objectId=689733