May 28, 2012

expert reaction to shift work and cancer

Working night shifts more than twice a week was found to be associated with an increased risk of breast cancer by a study published Occupational and Environmental Medicine.

Dr Lisa Wilde, Director of Research at Breast Cancer Campaign, said:

“Night shift working and breast cancer risk is a hugely complex area and two of the biggest risk factors – diet and physical activity outside of working hours – weren’t considered in this study. So, whilst it contributes to the debate, further research is needed to fully understand the link between night shift working, the lifestyle factors and breast cancer.”

Sarah Williams, Health Information Officer at Cancer Research UK, said:

“Scientists still can’t say for certain whether regularly working night shifts increases a woman’s risk of developing breast cancer and this particular study doesn’t settle that debate.

“Although this study found a higher risk for women working the greatest number of hours of night shifts altogether, they didn’t see a solid association if they analysed the data in other ways, for example when they looked at how many years of night shifts women had worked.

“The evidence so far seems to point to a probable link, but we still need more research to understand how big the risk could be and how many years it would take to appear.

“For the moment, there is strong evidence that women can reduce the risk of breast cancer by keeping to a healthy weight, drinking less alcohol and being physically active.”

Prof Debra Skene, Professor of Neuroendocrinology, University of Surrey, said:

“The study extends previous reports linking risk of breast cancer with working night shifts.

“The observation that ‘larks’ suffer more by working nights supports previous findings that early types (larks) cope less well with night work than late types (owls).

“Previous research has shown that the bigger the difference between a person’s internal biological clock and their work schedule (i.e. the greater the “social jetlag”) the greater the adverse effects of shift work (on sleep, cardiovascular and metabolic effects and now cancer).

“Although it has been hypothesised that light-induced suppression of night-time melatonin may be responsible for the increased incidence of cancer in shift-workers, this relationship has not been proven. Mismatch between a persons’ internal circadian timing and the imposed work schedule may better explain the cancer incidence. More studies are needed to assess the relationship between chronotype, shift schedules and the chronic adverse effects of working shifts.”

‘Nested case-control study of night shift work and breast cancer risk among women in the Danish military’ by Hansen et al., published in Occupational and Environmental Medicine on Monday 28th May 2012.