A prospective cohort research study analyzing the risks of coronary heart diseases (CHD) in the women who work late at nights was published in the Journal of Medical Association in the end April. The findings from the research study conducted on the women who worked as nurses suggested an increased risk of 15-18% of CHD as compared to the women who did not work in rotating shifts at night.

The American researchers examined the medical records of about 189,000 women over 24 years and found a significant link between ‘rotating shifts’ — alternate night and day work — and coronary heart diseases. Lifetime history of nurses who worked more than three night shifts per month, along with day and evening shifts, was evaluated from the Nurses’ Health Studies (NHS). The women also completed questionnaires about their known risk factors for heart disease every two to four years throughout the follow-up period. Moreover, the medical records provided information on everything from heart attacks to CHD-related chest pain. The number of deaths was confirmed by death certificates of the nurses.

The analysis was conducted using ‘Cox proportional hazards models’ and main outcomes of the study were found to be: CHD risks leading to death, non-fatal myocardial infarction, angiogram-confirmed angina pectoris, stents, angioplasty and coronary artery bypass graft surgery.

The study’s lead author Celine Vetter, along with her fellow colleagues, suggested that the underlying reason resulting in the incidents of CHD risks and death toll was linked with disturbances in the natural circadian rhythms in the body, also known as the body clock, which manages all the activities of the body. The researchers wrote in the JAMA report, “Circadian misalignment – where the [the body’s natural rhythm is out of step] with behavioral cycles of activity, sleep and food intake – may be a key mechanism linking shift work to chronic disease, including cardiovascular disease”.

Dr Celine Vetter — a renowned epidemiologist from Brigham and Women’s Hospital in Boston — while characterizing coronary artery diseases as a modifiable risk factor said that changing the schedules of shifts can possibly prevent the incidences of CHD to a great extent. The researchers made this conclusion after consulting the data sets provided by the hospital records and pointed out towards the unavailability of detailed information on exact work schedules. They believe that different schedules might have a different risk and believed that more research studies should be conducted on this topic to find out if shift patterns could be altered to reduce the risks.

The researchers also made it clear that the results concluded by their work were reported after controlling for the other risks factors for coronary heart disease, such as poor diet, lack of physical activity, elevated body mass index and smoking. They stated in the JAMA research paper, “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 shift work.”

A survey based study focusing the association between night work and cardiovascular diseases due to Korean working conditions was also published in 2015, in the PMC.

Another study published in the European Journal of Preventive Cardiology also evaluated the cardiovascular risk due to shifts in healthcare workers. Researchers believed that the detrimental health effect was caused due to the disturbance in the circadian rhythm of the night shift workers.

A US based cardiologist Dr Gregg Fonarow, a well-known cardiology professor at the University of California, Los Angeles, suggested that the rotating night shifts has been previously shown to be associated with an increased risk of diabetes and cardiovascular diseases, according to the CBC News.

Health statistics from the Centers for Disease Control and Prevention (CDC) report that 1 in every 4 deaths is caused by the heart diseases and as a result approximately 610,000 Americans die from heart disease every year. The coronary heart disease specifically is the most common type of heart disease, which kills more than 370,000 people annually.

The British Heart Foundation defines coronary heart diseases as the heart complications formed due to the ineffective working of the coronary arteries. These arteries have been associated with the task of supplying oxygenated blood to the heart. Sometimes theses arteries fail to carry enough blood to the heart due to the blockage caused by fatty materials within the walls, leading to a bigger complication known as atherosclerosis. As a result, the pain and discomfort is experienced by the heart and is known as angina. Furthermore, if a portion of the fatty material, known as atheroma, breaks off in the arteries, it can form a blood clot which breaks the oxygen rich blood supply to the heart, putting stress on the heart and can thus cause a heart attack.

The other risks factors which can cause the coronary heart diseases are: smoking, high blood pressure, high blood cholesterol, diabetes, physical inactivity, obesity, family history of heart disease and ethnic background along with gender and age.