Chuck Bednar for redOrbit.com – Your Universe Online
Women who regularly work night shifts are at greater risk of death resulting from lung cancer and cardiovascular disease (CVD), an international team of researchers report in the latest edition of the American Journal of Preventive Medicine.
The authors of this new paper reviewed data from the Nurses’ Health Study (NHS), a study of nearly 75,000 registered American nurses, and found that those working rotating night shifts for five or more years appeared to have a modest increase in all-cause and CVD-related death.
Furthermore, those working 15 or more years of rotating night shift work also appeared to have a modest increase in lung cancer mortality. The authors said that their findings add to the mounting evidence that rotating night shift work can adversely affect a person’s health and longevity.
As they pointed out in a statement Monday, the World Health Organization (WHO) classified night shift work as a probably carcinogen in 2007 due to the way is disrupts a person’s circadian rhythms. Sleep and the circadian system, they said, play a key role in cardiovascular health and antitumor activity, and there is “substantial biological evidence” that working the night shift can enhance the development of cancer and cardiovascular disease.
In their research, the authors analyzed more than two decades of follow-up data and found that working night shifts for over five years was associated with increases in the risk of all-cause and CVD-related deaths.
They found an 11-percent increase in all-cause mortality for women with six to 14 years or more than 15 years of rotating night shift work. Cardiovascular-related morality appeared to increase by 19 percent and 23 percent for those groups, respectively, and those who worked nights for at least 15 years faced a 25 percent increased risk of lung cancer, the study authors found.
The NHS, which was based at Brigham and Women’s Hospital in Boston, started in 1976 and involved more than 120,000 US female nurses between the ages of 30 and 55. Each participant answered biennial follow-up questionnaires, and night shift information was first collected in 1988. More than 85,000 nurses responded to those inquiries, according to the researchers.
Women with pre-existing cardiovascular issues and cancers other than non-melanoma skin cancer were excluded, leaving nearly 75,000 women that were included in the analysis. Rotating night shift work was defined as working at least three nights per month in addition to days and evenings during the same month, and each woman was asked how many years they had worked those schedules (1-2, 3-5, 6-9, 10-14, 15-19, 20-29 or more than 30 years).
Dr. Eva S. Schernhammer, an associate professor of medicine at Harvard Medical School, called the study “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.”
“These results add to prior evidence of a potentially detrimental relation of rotating night shift work and health and longevity,” she added. “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 (e.g., chronotype) warrant further exploration.”
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