Previous studies have shown that shift workers have increased risk of heart attack, stroke, and other cardiovascular complications. This finding has been controversial as some of the studies have been thought to be flawed in data analysis and methodology. Despite this, many in the medical community have held on to the theory that shift work imparts an increased cardiovascular risk. Controlling the traditional risk factors for cardiovascular disease, such as diabetes, hypertension, cholesterol levels, and encouraging smoking cessation has been recommended for these workers.
Researchers, lead by Dr. Daniel Hackam from the Stroke Prevention and Atherosclerosis Research Centre in London, Ontario, Canada, have added to the existing evidence that shift workers have an increased risk of developing cardiovascular complications such as heart attack and stroke. The results of their study were published online in the British Medical Journal. The objective of the study was to analyze the existing evidence regarding the association between shift work and major cardiovascular events as previously reported in the medical literature. The researchers used systematic searches of literature databases, interviews with experts in the field, and review of articles and papers. Published observational studies that reported risk ratios for myocardial infarction, ischemic stroke, any coronary event, and all cause mortality in relation to shift work were used for analysis. There were 34 studies that included over 2 million participants used for the current analysis. The researchers confirmed the previous finding that shift work is associated with myocardial infarction and ischemic stroke. Other coronary events were also increased in the study findings, but the investigators did not find an increased risk of mortality with shift work. Adjusting for smoking and socioeconomic status did not change these results.
The authors wrote, “In a comprehensive, up to date review of all available literature, we found that shift work was associated with coronary and cerebrovascular events… Our findings have several implications. The increased risk of vascular disease apparent in shift workers, regardless of its explanation, suggests that people who do shift work should be vigilant about risk factor modification. Screening programmes for modifiable risk factors in shift workers have yielded substantial burdens of treatable risk factors, including dyslipidaemia, smoking, glucose intolerance, and hypertension. Shift workers should be educated about cardiovascular symptoms in an effort to forestall or avert the earliest clinical manifestations of disease”.
This finding is not surprising and adds to the already existent database of evidence that suggests that shift work increases cardiovascular events. It is hoped that this new study helps to convince the medical community to encourage risk factor reduction in shift workers. Shift work has long been suspected to prevent normal circadian rhythms, impair normal sleep patterns, and disrupt work-life balance. Our industrialized society needs shift workers to remain a fully productive economy. Future studies are needed to determine how to modify shift schedules to decrease their associated cardiovascular risk. In addition, we should work to identify those individuals who are more vulnerable to the effects of shift work in order to prevent cardiovascular events by decreasing other modifiable risk factors.
Manav V. Vyas et al. “Shift work and vascular events: systematic review and meta-analysis” BMJ 2012: 345 doi: 10.1136/bmj.e4800