MedicalResearch.com Interview with:
Dr. Céline Vetter, Dr.Phil.
Instructor in Medicine
Harvard Medical School
Channing Division of Network Medicine
Brigham and Women’s Hospital
Boston, MA, 02115
MedicalResearch.com: What is the background for this study?
Response: Heart Disease is still the leading cause of death in the US, with 1 in every 4 deaths being attributed to heart disease. On the other hand, it is estimated that approximately 15 millions Americans work evening shifts, night shift, rotating shifts or any other kind of irregular schedule that is arranged by the employer. The link between shift work and coronary heart disease has been studied for decades now, but because shift work can take so many forms, results have not been consistent. Another contributing factor to this inconsistency might be that few studies could actually track individuals over long periods of time, so that some studies might have missed when participants did actually develop coronary heart disease.
Our study was based on the Nurses’ Health Studies I and II, where women about 189,000 registered female nurses completed every two years mailed questionnaires that comprise items about their health status, medical history, and known or suspected risk factors for cancer and heart disease. They also reported their lifetime history of rotating night shift work in 1988 and 1989, respectively. Across the 24 years of the study periods, we observed more than 10,000 cases of coronary heart disease (i.e. myocardial infarction, CHD death, angiogram-confirmed angina pectoris, and procedures related to coronary heart disease, i.e. angioplasty, coronary artery bypass graft surgery or stents).
MedicalResearch.com: What are the main findings?
Response: Overall, we observed a modest increased risk of coronary heart disease associated with rotating night shift work, and this risk increased with longer duration of shift work. In both cohorts, women who worked more than 10 years of rotating night shift work had 15% and 18% increased risk of developing coronary heart disease as compared with women who did not work rotating night shifts, after taking into account known risk factors of coronary heart disease. Our results also suggested that recent shift work might be most relevant for CHD risk. We also observed that longer time since quitting shift work was associated with a decreased CHD risk, further supporting the hypothesis that the risk of coronary heart disease associated with shift work might wane over time, when women stopped working shifts. This is a new finding that warrants replication.
MedicalResearch.com: What should clinicians and patients take away from your report?
Response: There is a number of known risk factors for coronary heart disease, such as smoking, low quality diet, lack of physical activity, and elevated BMI. Those are crucial when we are thinking about how to prevent coronary heart disease.
However, an important take home message is that even after controlling for these risk factors, we still saw an increased risk of coronary heart disease associated with longer duration of rotating night shift work. This risk also appears to wane after stopping shift work, which is a novel finding and warrants replication.
It is also important to know that overall a small proportion of women in our sample had an increased CHD risk, namely 15%. And even though the absolute risk is small, and the contribution of shift work to coronary heart disease is modest, this is a modifiable factor, and changing schedules might help prevent coronary heart disease.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: It is possible that different work schedules might carry a different risk, and we have very little information on exact schedules, as well as work start and end times. Future studies are needed that collect that level of detail so we can better understand which aspects of shift work are most critical. We also do not well understand who is at highest risk. Individual characteristics, such as chronotype – that is the individual’s endogenous biological rhythm, which is disrupted, especially in rotating night shift workers – and information on sleep patterns and quality, might modulate this risk.
We believe that the results from our study underline the need for future research to further explore the relationship between work schedules, individual characteristics, and coronary health.
Eva S. Schernhammer, MD, DrPH et al. Association Between Rotating Night Shift Work and Risk of Coronary Heart Disease Among Women.JAMA, April 2016 DOI: 10.1001/jama.2016.4454
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