Up to one in four jobs are "high strain," and people in these lines of work may be at increased risk of stroke, according to a new analysis of past research.

Based on studies that included nearly 140,000 participants, researchers found an overall 22 percent higher stroke risk among those in high-strain jobs versus low-strain occupations. In some cases, the risk was elevated by up to 58 percent.

Previous studies of work stress and stroke had been inconsistent, senior author Dr. Dingli Xu of Southern Medical University in Guangzhou, China, told Reuters Health.

Plenty of research has linked job strain to heart disease in general and high blood pressure in particular, he and his coauthors note in Neurology. Using a well-established formula, these kinds of studies usually define high-strain jobs as those with high demands and little control over decision-making.

Xu's team considered the data from six studies involving a total of 138,782 participants who were followed for three to 17 years. They used an existing system to classify job stress based on demands, such as time pressure, mental load or coordination, and control, such as the worker's ability to decide when or how they complete tasks.

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According to these categories, passive jobs, like janitors or manual laborers, have low demands and low control. Low stress jobs, like architects or scientists, have low demand and high control. Active jobs, like doctors, teachers and engineers, have high demand and high control.

None of those types of jobs were tied to an increase in stroke risk in the new study, but people with high stress jobs involving high demand and low control, like waitresses and nurses, were 22 percent more likely to suffer a stroke than people with low stress jobs.

The risk was 33% higher among women in high-strain jobs compared to those in low-strain jobs. And in both sexes, the risk of ischemic stroke - which is usually caused by a clot that blocks blood flow to the brain - was 58 percent greater in the high strain jobs group compared to those in low-strain jobs. The other common form of stroke, hemorrhagic, which is caused by a broken blood vessel in the brain, was less linked to job strain.

The inconsistency of past studies in finding links between job strain and stroke risk may be caused by "different methods used to evaluate work stress, different psychological responses in men and women and different social culture with the studied populations," Xu told Reuters Health by email.

The original studies accounted for some factors, like sex and age, but did not account for important risk factors like high blood pressure or cholesterol levels.

"I think that everyone intuitively knows that stress increases illness in general, and this shows work stress increases stroke risk," said Dr. Jennifer J. Majersik with the University of Utah in Salt Lake City, who wrote an editorial accompanying the new study.

But other factors like smoking, high blood pressure and diabetes are still "off the chart more important," she told Reuters Health.

In modern society, stress from work may be the most important source of psychological strain, but perceived stress of certain jobs may be different in different countries, due to the effect of different social culture, Xu said.

Most patients believe that stress contributed to their stroke, and based on this analysis, that is likely accurate, Majersik said.

Although this was not tested, it makes sense that increasing control in high-stress jobs could relieve some strain and may mitigate some stroke risk, she said.

"Things like telecommuting, flexible work hours, allowing decision making to not be as top heavy, allowing people to make decisions about their own jobs," would be an amazing public health intervention, she said.