Working in rotating night shifts may increase the risk of cardiovascular disease and lung cancer, a new study has warned.
Night shift work has been consistently associated with higher risk for cardiovascular disease (CVD) and cancer. In 2007 the World Health Organisation classified night shift work as a probable carcinogen due to circadian disruption.
In the new study, researchers found that women working rotating night shifts for five or more years appeared to have a modest increase in all-cause and CVD mortality and those working 15 or more years of rotating night shift work appeared to have a modest increase in lung cancer mortality.
These results add to prior evidence of a potentially detrimental effect of rotating night shift work on health and longevity, researchers said.
Sleep and the circadian system play an important role in cardiovascular health and anti-tumour activity. There is substantial biological evidence that night shift work enhances the development of cancer and CVD, and contributes to higher mortality.
An international team of researchers investigated possible links between rotating night shift work and all-cause, CVD, and cancer mortality in a study of almost 75,000 registered US nurses.
Using data from the Nurses' Health Study (NHS), the authors analysed 22 years of follow-up and found that working rotating night shifts for more than five years was associated with an increase in all-cause and CVD mortality.
Mortality from all causes appeared to be 11 per cent higher for women with 6-14 or 15 years of rotating night shift work. CVD mortality appeared to be 19 per cent and 23 per cent higher for those groups, respectively.
There was no association between rotating shift work and any cancer mortality, except for lung cancer in those who worked shift work for 15 or more years (25 per cent higher risk).
The NHS, which is based at Brigham and Women's Hospital, Boston, began in 1976, with 121,700 US female nurses aged 30-55 years, who have been followed up with biennial questionnaires.
Night shift information was collected in 1988, at which time 85,197 nurses responded. After excluding women with pre-existing CVD or other than non-melanoma skin cancer, 74,862 women were included in this analysis.
Defining rotating shift work as working at least three nights per month in addition to days or evenings in that month, respondents were asked how many years they had worked in this way.
The study was published in the American Journal of Preventive Medicine.