Night Shift Risks

Increased risk of coronary heart disease seen among women who work rotating night shifts

Image: iStock.

Image: iStock.

Heart disease is the leading cause of death in the United States. In a new study from Brigham and Women’s Hospital and Harvard Medical School published in the April 26 issue of JAMA, researchers found that women who work more than 10 years of rotating night shift work had a 15 to 18 percent increased risk of developing coronary heart disease, the most common type of heart disease, as compared with women who did not work rotating night shifts.

“There are a number of known risk factors for coronary heart disease, such as smoking, poor diet, lack of physical activity and elevated body mass index. These are all critical factors when thinking how to prevent coronary heart disease. However, even after controlling for these risk factors, we still saw an increased risk of coronary heart disease associated with rotating shift work,” said lead author Celine Vetter, an HMS instructor in medicine and a chronobiologist at Brigham and Women’s. “Even though the absolute risk is small and the contribution of shift work to coronary heart disease is modest, it is important to note that this is a modifiable risk factor, and changing shift schedules may have an impact on the prevention of coronary heart disease.”

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Researchers examined the association between rotating night shift work and coronary heart disease over a period of 24 years. About 189,000 women in the Nurses’ Health Study I and II who reported their lifetime exposure to rotating night shift work (defined as three or more night shifts per month, in addition to day and evening shifts) in 1988 and 1989 were included in the analysis.

These women also reported on their coronary health, indicating whether they had an angiogram that confirmed coronary heart disease-related chest pain, a heart attack or cardiovascular procedures such as angioplasty, coronary artery bypass graft surgery or stents. 

In the case of a self-reported heart attack, or death, information was confirmed by medical records and death certificates to ensure that the event was related to coronary heart disease.

Questionnaires also collected data on known risk factors of coronary heart disease every two to four years throughout the study period. Over the 24-year period, more than 10,000 newly developed cases of coronary heart disease occurred.

In addition, researchers also found that recent shift work might be most relevant for coronary heart disease risk and that longer time since stopping shift work was associated with decreased coronary heart disease risk, a new finding that researchers note warrants replication.

“Our results are in line with other findings, yet it is possible that different schedules might carry a different risk, and we have very little information on exact schedules, as well as work start and end times,” said Vetter, who is also an associate epidemiologist in the Channing Division of Network Medicine. “We believe that the results from our study underline the need for future research to further explore the relationship between shift schedules, individual characteristics and coronary health to potentially reduce coronary heart disease risk.”

Researchers note that individual characteristics such as the individual’s biological rhythm, disrupted in rotating night shift workers, and information on sleep patterns and quality might modulate coronary heart disease risk.

This study was supported by the Centers for Disease Control and Prevention/The National Institute for Occupational Safety and Health grant 5R01OH009803, UM1CA176726 and R01HL034594 and a fellowship from the German Research Foundation.

 Adapted from a Brigham and Women’s Hospital news release.