More bad news for late-shift workers: Their odd hours may be raising their risk of heart attack and stroke.
So says a new, large-scale study in the British Medical Journal that adds these two problems -- which fit into a broader category known as vascular disease -- to the previously known risks of shift work. Previous research had suggested that working the graveyard shift, the swing shift or any irregular shift other than the traditional 9-to-5 is linked to high blood pressure, diabetes and obesity.
British and Canadian researchers analyzed the findings of 34 studies that included more than 2 million people who had work schedules including anything other than regular daytime hours. They found that shift work was linked to a 23 percent increased risk of heart attack and a 5 percent increased risk of stroke. Those working night shifts seemed to be at the highest risk.
The study authors said it pays for workers to know that their jobs may put them at increased risk.
"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," they wrote in the report.
A variety of factors -- not just the shift work itself -- could be culprit in increasing the risk of heart attack and stroke for people in those occupations. A lack of sleep, poor eating habits and lower levels of physical activity could plague those who work irregular hours and drive up the risk of vascular disease.
Dr. Robert Bonow, professor of medicine at Northwestern University Feinberg School of Medicine and past president of the American Heart Association, said it's possible that people working jobs requiring shift work may be economically disadvantaged and have less access to health care -- two factors generally associated with unfavorable health outcomes.
However, the study authors noted that the increased risk of vascular events was still present even when they accounted for things like unhealthy eating, smoking and socioeconomic status -- evidence that something about the nature of shift work other than poor health behaviors might be at play.
But what could it be? One possibility is disruption in circadian rhythm, a feature inherent in shift work. These disruptions can certainly have an effect on heart rate and blood pressure -- two measures intimately tied to vascular health, said Dr. Carl Lavie, a cardiologist at Ochsner Medical Center in New Orleans.
Since shift work is a necessary evil for more than a third of the working population, it is unreasonable to think that everyone can simply change their schedules.
"My advice would be to exercise and make sure their fitness is at a high level, and then I'd treat their risk factors vigorously," Lavie said. He added that if you are a shift worker it is important to recognize that treatments you might be getting for blood pressure control, weight control and cholesterol may be more important for you than someone at a lower risk.
Bonow agreed. "There's somewhat of a signal here, and people who do shift work should be aware that their risk factors should be identified and managed."