(CBS News) Working the overnight shift may dramatically increase your risk for a heart attack, new research suggests.
Shift work is defined as employment outside of a traditional "9 to 5" daytime schedule, including regular evening or night shifts, rotating or split shifts that can vary in time depending on the day or week and other irregular work schedules.
Previous research has linked such shifts to a raised risk for health problems including obesity and diabetes, because the inconsistent shifts - which are often economically necessary for some industries such as transportation - disrupt the body's natural sleep cycle, the circadian rhythm and work-life balance.
Now, the largest study of shift work to date that looked at heart health has found that workers may face an increased risk for heart problems such as strokes and heart attacks.
For the new research, published online July 26 in British Medical Journal, scientists analyzed results from 34 earlier studies involving more than 2 million people. Out of those, about 17,350 had some sort of heart event with 6,600 having a heart attack and 1,850 having an ischemic stroke, caused by lack of oxygen to the brain.
A closer look found such heart problems were more common in shift workers: They were 24 percent more likely to experience a coronary event, 23 percent more likely to have a heart attack and 5 percent more likely to suffer a stroke. The risk increases remained the same after ruling out the study participants' unhealthy behaviors.
Night-shift workers were found to fare worst, with a 41 percent increase in risk of having a coronary event. Shift workers, however, were not more likely to die from any cause compared with their daytime-working counterparts.
Study author Dr. Daniel G. Hackman, assistant professor of medicine at the University of Western Ontario in Canada, told WebMD that while the studies he and his team reviewed were observational and only suggested an association between heart problems and shift work, "the relationship is probably causal."
The study's authors say their research could lead to more targeted screening programs to identify health risks in shift workers in addition to programs to educate workers on their risk.
"If you are a shift worker, know your cardiovascular risk factors cold," Hackman said. "Go see your family doctor and get an annual physical. And ask for measurement of your blood pressure, waist circumference, cholesterol, triglycerides and fasting blood sugar."
This isn't the first study to find that shift workers face health risks from their varying schedules. Recent research finds that shift workers may decrease their metabolism and experience spikes in blood sugar after eating,.
A recent poll from the National Sleep Foundation found one in five pilots make a serious error at work because they are tired.
Jan White, research and information services manager at the Institution of Occupational Safety and Health in the U.K. told the BBC that risks can go beyond heart problems, raising psychological and substance abuse risks.
"It can result in disturbed appetite and digestion, reliance on sedatives and, or stimulants, as well as social and domestic problems," White said. "These can affect performance, increase the likelihood of errors and accidents at work and even have a negative effect on health.