A new study of U.S. nurses has found that working a rotating night shift can be dangerous to your health.
Prior research had suggested that night shift work is associated with higher risk for cardiovascular disease (CVD) and cancer. In 2007 the World Health Organization classified night shift work as a probable carcinogen due to circadian disruption.
In the current investigation, 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.
Moreover, those working 15 or more years of rotating night shift work appeared to have a modest increase in lung cancer mortality.
The study can be found in the American Journal of Preventive Medicine.
Experts are aware that sleep and the circadian system play an important role in cardiovascular health and antitumor activity. For the current study, 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 U.S. nurses.
Using data from the Nurses’ Health Study (NHS), the authors analyzed 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 percent higher for women with six to 14 or 15 years of rotating night shift work. CVD mortality appeared to be 19 percent and 23 percent higher for those groups, respectively.
Investigators did not find an association between rotating shift work and any cancer mortality, except for lung cancer in those who worked shift work for 15 or more years (a 25 percent higher risk).
The NHS, which is based at Brigham and Women’s Hospital in Boston, began in 1976, with 121,700 U.S. 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.
Rotating shift work is defined as working at least three nights per month in addition to days or evenings in that month. In the survey, respondents were asked how many years they had worked in this way. The prespecified categories were never, one to two, three to five, six to nine, 10-14, 15-19, 20-29, and >30 years.
According to Eva S. Schernhammer, M.D., Dr.P.H., of Harvard Medical School and Brigham and Women’s Hospital, this study “is one of the largest prospective cohort studies worldwide with a high proportion of rotating night shift workers and long follow-up time.
“A single occupation (nursing) provides more internal validity than a range of different occupational groups, where the association between shift work and disease outcomes could be confounded by occupational differences.”
Schernhammer believes the study is powerful as the results “add to prior evidence of a potentially detrimental relation of rotating night shift work and health and longevity.”
She also believes additional research is needed to derive practical implications for shift workers and their health. This knowledge would help hospitals determine the role of duration and intensity of rotating night shift work and improve the ability to match shift schedules with individual traits (e.g., chronotype).