People working night shifts had the highest risk of a coronary event (41 percent), 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.
In Canada, for example, almost 33 percent of workers were shift workers in 2008-2009. In all, during that time, 7 percent of heart attacks, 7 percent of all coronary events and almost 2 percent 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 recognize 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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