Working night shifts increases all-cause and cardiovascular disease
6 January 2015
A 22 year study of nurses in the US found that rotating
night shifts for five or more years increases all-cause and CVD
mortality and those working 15 or more years of rotating night shift
work had an 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.
Sleep and the circadian system play an important role in
cardiovascular health and antitumor 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 analyzed 22
years of follow-up
Mortality from all causes appeared to be 11% higher for women
with 6-14 or ≥15 years of rotating night shift work. CVD mortality
appeared to be 19% and 23% 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% higher risk).
The Nurses’ Health Study, which is based at Brigham and Women’s
Hospital, 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
According to Eva S. Schernhammer, MD, DrPH, currently Associate
Professor of Medicine, Harvard Medical School, and Associate
Epidemiologist, Department of Medicine, Brigham and Women's
Hospital, Boston, 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.”
Comparing this work with previous studies, she continued, “These
results add to prior evidence of a potentially detrimental relation
of rotating night shift work and health and longevity ... To derive
practical implications for shift workers and their health, the role
of duration and intensity of rotating night shift work and the
interplay of shift schedules with individual traits (eg chronotype)
warrant further exploration.”
Fangyi G, et al. Total and Cause-Specific Mortality of U.S.
Nurses Working Rotating Night Shifts. American Journal of Preventive
Medicine, published online ahead of Volume 48, Issue 3 (March 2015),