In 2007, the World Health Organization officially classified night shift work as a probable carcinogen due to circadian disruption. Your circadian rhythms are physical, mental, and behavioral changes responding to light and darkness in your environment that occur within a 24 hour cycle. They affect body functions and health as abnormal circadian rhythms have been linked to conditions including sleep disorders, obesity, diabetes, depression, and bipolar disorder. Sleep and the circadian system are largely important in heart health and anti-tumor activity.
Substantial biological evidence shows that night shift work enhances cancer and CVD developments, as well as contributes to higher mortality. The American Journal of Preventive Medicine published a study involving women working rotating night shifts and the associated mortality risks. Women working night shifts for five or more years had a modest increase in all-cause and cardiovascular disease (CVD) mortality. Those working 15 years or more of rotating night shifts had a modest increase in lung cancer mortality.
The study of registered nurses in the United States and was led by an international team of researchers that investigated possible links associated with rotating night shift work and all-cause, CVD, and cancer mortality. Researchers analyzed 22 years of follow-up data from the Nurses’ Health Study (NHS) and found more than five years of working rotating night shifts appeared to be connected with an increase in all-cause and CVD mortality.
By The Numbers
The NHS began in 1976 at Brigham and Women’s hospital with 121,700 female nurses between the ages of 30 to 55. Night shift information was collected from 85,197 nurses in 1988. Of that group, only 74,862 women were included in this recent analysis after excluding the women with pre-existing CVS or cancer. Respondents were asked to answer how many years they had worked at least three nights in addition to days or evenings per month. Women with 6 to 14 years of night shift work had a 11% higher mortality from all causes. CVD mortality was 19% and 23% higher for those groups. The only cancer mortality that showed association with rotating shift work was lung cancer, with a 25% higher risk in those who did night shift work for 15 or more years.
Unlike most prior studies on graveyard shift workers, this one focused solely on people working in the same occupation. The results add to prior consistent evidence of the potential detrimental role rotating night shift work plays on health and longevity.