Sixty seconds on . . . night shifts

BMJ 2016; 355 doi: (Published 11 October 2016) Cite this as: BMJ 2016;355:i5476
  1. Anne Gulland
  1. The BMJ

Shh! I’m trying to sleep after my night shift

This is worth staying awake for. New research has shown that working nights is not, after all, linked to an increased risk of breast cancer. Prospective studies of nearly 800 000 UK women, combined with other findings, showed that women who worked nights (including those who had worked nights for 20 to 30 years) were no more likely to develop breast cancer than women who had never done night shifts.1


This is a major shift (no pun intended) in thinking. The World Health Organization’s International Agency for Research on Cancer (IARC) had previously categorised shift work involving “disruption of the circadian rhythm” as a probable carcinogen.2 But this was based on evidence on breast cancer from animal studies.

Circadian disruption?

The agency thought that exposure to light at night alters sleep patterns, suppresses melatonin production, and may affect genes involved in tumour development. However, this new study says that the evidence reviewed by IARC was not strong enough to assess risk.

I’m going back to sleep now

Hold on a second. Observational studies have found that working shifts was associated with a 9% increased risk of type 2 diabetes when compared with working standard daytime hours. The risk was 37% higher in men and 42% higher in people whose shift patterns changed.3

What hath night to do with sleep?

Further evidence that not sleeping at night may affect health comes from studies linking shift work to and increased risk of cardiovascular disease and stroke and also depression.4 5 And the new study found that women doing night shifts were more likely to be obese and to smoke.1

I’ll just make myself a coffee

That’s fine. A recent review from IARC found no conclusive evidence that drinking coffee is carcinogenic. But don’t make it too hot, as the group warned that very hot drinks may cause cancer of the oesophagus.6



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