After controlling for such factors as smoking, alcohol consumption and physical activity, the researchers found that people working between 41 hours and 48 hours had a 10 percent higher risk of stroke than those working a more normal schedule of 35 to 40 hours a week. Those working 49 hours to 54 hours, had a 27 percent higher risk; and those working 55 or more hours, a scary 33 percent greater risk.
“Long working hours are not a negligible occurrence,” Urban Janlert, a researcher from the Umea University in Sweden, wrote in a commentary. Janlert pointed out that in many countries, a high percentage of workers put in more than 50 hours a week — which probably puts them at risk for devastating events such as stroke or conditions including heart disease.
Janlert said he wondered whether long working hours is an “avoidable cause of stroke” and called the study the “strongest indication of a causal association.” Prevention of stroke and heart disease has focused almost exclusively on measures such as diet, exercise and medicine. But studies similar to this one have shown that work conditions can also be critically important.
“Essentially, if long working hours present a danger to health, it should be possible to change them, which is not always the case with other work environmental factors,” Janlert wrote.
Study author Mika Kivimaki, a professor of epidemiology and public health, and her colleagues found a similar but more modest link between working long hours and an increased risk of coronary heart disease in a separate meta-analysis they conducted. Those who worked 55 hours or more a week had a 13 percent increased risk of a new diagnosis, hospitalization or death from heart disease.
“The pooling of all available studies . . . allowed us to investigate the association between working hours and cardiovascular risk with greater precision than has previously been possible,” Kivimaki said in a statement.
Concern over the impact of long hours on a person’s health has been growing in recent years. Earlier this month, a study in the journal Occupational & Environmental Medicine by researchers at Harvard and the Centers for Disease Control and Prevention found that working more than 40 hours a week and regularly engaging in heavy lifting may adversely impact a woman’s ability to become pregnant.
Research participants consisted of 1,739 female nurses who wanted to conceive, and those who worked more than 40 hours took 20 percent more time to get pregnant compared with those working 21 to 40 hours.