The best way to lower the risk of heart attack and stroke associated with shift work is to keep the usual risk factors - such as blood pressure, cholesterol, weight and diabetes - under control, experts say.
"Given the commonness of shift work in modern industrialised nations, and industrialising nations, many heart attacks and strokes are likely directly attributable to the effects of shift work," said lead researcher Dr Daniel Hackam, a clinical pharmacologist at the Stroke Prevention and Atherosclerosis Research Centre in London, Ontario, Canada.
Screen shift workers
Employers and employees must be aware of this problem, as should doctors and others who see shift workers, he said.
"Shift workers should receive cardiovascular risk factor screening and prevention, and this should be ongoing and regular," Hackam added.
Particular attention should be paid to risk factors that may be worsened by shift work, such as blood pressure, cholesterol and diabetes, he noted.
"Since we are now in a 24/7 society, this problem is not likely to go away any time soon," Hackam pointed out.
The report was published online in the BMJ.
How the study was done
To look at the connection between heart attack, stroke and shift work, Hackam's group analysed 34 studies that included more than 2 million people.
This process of pooling results from different studies is called a meta-analysis, and is used by researchers to uncover patterns that are consistent across a large population.
Among the people in these studies, more than 17 000 had some kind of cardiovascular problem. More than 6,500 had heart attacks and almost 1 900 had strokes, the research showed.
Hackam's team found that shift workers had a nearly 25% increased risk of having a cardiovascular problem, a 23% increased risk of a heart attack and a 5% increased risk of a stroke when compared to non-shift workers.
People working night shifts had the highest risk of a coronary event (41%), they added.
Although the increased risks are small, because many people are shift workers the number of people at risk is substantial, the researchers explained.
What the study showed
In Canada, for example, almost 33% of workers were shift workers in 2008-2009. In all, during that time, 7% of heart attacks, 7% of all coronary events and almost 2% of strokes could be attributed to shift work, the investigators noted.
While this type of study can show an association between two factors, it does not prove a cause-and-effect relationship.
Dr Gregg Fonarow, a professor of cardiovascular medicine at the University of California, Los Angeles, said that "a number of prior studies have suggested that working outside of regular daytime hours may be associated with an increased risk of cardiovascular events and stroke."
This new study finds shift work is associated with a higher risk of coronary events and stroke, he noted. But an increase in all-cause mortality with shift work was not seen.
"While the increase in cardiovascular risk was modest, with as many as 15 million Americans working full-time on evening shift, night shift or other irregular schedules, these findings may have important public health implications," Fonarow said.
"Individuals with these types of work schedules should recognise the potential increase in risk for cardiovascular events and stroke, and take proactive steps to improve their cardiovascular health," he added.
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For more on heart disease, visit the U.S. National Library of Medicine.
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