Celine Vetter

Heart disease is the leading cause of death in the U.S., contributing to one in every four deaths. In a new BWH study published in the Journal of the American Medical Association, researchers found that women who have performed rotating night shift work for more than 10 years had a 15 to 18 percent increased risk of developing coronary heart disease (CHD)—the most common type of heart disease—compared to women who did not work rotating night shifts.

“There are a number of known risk factors for CHD, such as smoking, poor diet, lack of physical activity and elevated body mass index (BMI),” said lead author Celine Vetter, PhD, associate epidemiologist in the Channing Division of Network Medicine and a chronobiologist at BWH. “These are all critical factors when thinking how to prevent CHD; however, even after controlling for these risk factors, we still saw an increased risk of CHD associated with rotating night shift work. Even though the absolute risk is small, and the contribution of shift work to CHD 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 CHD.”

Researchers examined the association between rotating night shift work and CHD 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) were included in the analysis. These women also reported on their heart health, indicating whether they had CHD-related chest pain, a heart attack or cardiovascular procedures such as angioplasty, coronary artery bypass graft surgery or stents. In the case of a death or self-reported heart attack, information was confirmed by death certificates and medical records to ensure that the event was related to CHD. Questionnaires also collected data on known risk factors of CHD every two to four years throughout the study period. Over the 24-year period, more than 10,000 newly developed cases of CHD occurred.

Researchers also found that recent night shift work might be most relevant for CHD risk. Additionally, for women who stopped working shifts, a longer time since quitting was associated with a decreasing CHD risk, a new finding that researchers note warrants replication.

“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 CHD risk,” Vetter said.

Researchers note that the individual’s biological rhythm—which is often disrupted in rotating night shift workers—along with sleep patterns and quality might modify the association of CHD with shift work. Together with more detailed information on work schedules, future studies might help identify which aspects of work schedules are most critical and who is at highest risk.