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Putting in those extra hours at the office could be raising your blood pressure, according to a new study.

Researchers from the University of California, Irvine, have found that working longer hours is directly associated with hypertension, even after adjusting for biological risk factors such as gender and ethnicity.

“We know that males, for example, or African Americans, are more likely to have hypertension. But once we controlled for that, what we found was that the number of hours people worked per week was still independently and significantly associated with higher rates of hypertension,” said Dean Baker, senior author of the study and director of UC Irvine's Center for Global Occupational and Environmental Health.

From 55,000 households surveyed at random as part of the 2001 California Health Interview Survey, the study — published today in the American Heart Association journal Hypertension — analyzed the information of 24,000 adults who worked more than 11 hours a week.

Compared with those working between 11 and 39 hours a week, people who put in between 40 and 51 hours were 17-per-cent more likely to report hypertension. Those who worked more than 51 hours were 30-per-cent more likely.

That is significant, Dr. Baker said, because hypertension is known to drastically increase the risk of heart attack and stroke.

The authors cite several possible reasons why working longer hours leads to hypertension, including shorter recovery time (and less sleep), poor eating habits, lack of exercise and longer exposure to psychosocial factors, such as job strain, in the work environment.

Because of the study's large size, the researchers were able to analyze data of people in very different jobs, from corporate executive to assembly-line attendant. Dr. Baker said it was clerical and blue-collar workers who reported higher rates of hypertension.

“If you go back 20 or 25 years ago, the classic concept of occupational stress was that the executive and the professionals who have a lot of time demands on them were the ones who had high blood pressure. But when people started looking at it closely, that's not actually true.”

It turns out that people in jobs that place high demands on them but give them low control over the conditions have more stress.

Sheldon Tobe, a nephrologist at Sunnybrook Health Sciences Centre in Toronto and a researcher for the Heart and Stroke Foundation of Ontario, said that phenomenon is consistent with a study he conducted earlier this year looking at rates of hypertension among health-care professionals.

“The longer hours are only going to affect a minority of people, although a significant minority,” he said, noting the examples of an operating-room nurse and an air-traffic controller.

“It's high job demand and low job decision-making. Even if he or she wants to go to the bathroom, they have to put up their hand.”

And while Canadians are seeing an increase in hypertension rates, many people still do not know they have high blood pressure, because often there are no symptoms.

“If you're feeling stress at work and you're working long hours, see your family physician and have your blood pressure measured,” Dr. Tobe said. “No one should panic from this, but it is just more and more evidence that stresses in our environment really do have an impact on us.”