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Ongoing hassles at work are a real threat to health because they can raise blood pressure over the long term – right?

Wrong.

While no one disagrees that a fight with the boss can send blood pressure skywards for an hour or so, the most comprehensive review of the literature on the subject ever conducted finds little evidence that day-to-day work woes affect chronic blood pressure, one way or the other.

"It's long been a cherished notion that chronic stress in this case, job stress contributes to hypertension. It's time to set the record straight, however," says Dr. Samuel J. Mann, professor of clinical medicine at Weill Medical College of Cornell University and a hypertension specialist at NewYork-Presbyterian Hospital/Weill Cornell Medical Center in New York City.

"When you realize that doctors may be advising patients to quit or change jobs to help them avoid hypertension, it's clear that this misconception can have life-altering effects," Dr. Mann points out.

His review of dozens of studies on the subject, published in the May issue of Current Hypertension Reviews, finds that the evidence that workplace stress has a lasting effect on blood pressure is very weak and very inconsistent.

His review was spurred, in part, by a very rigorous study published in 2003 by a team of French researchers in the prestigious journal Hypertension.

That study found no effect of job strain on hypertension. "So, I wondered, if this very large, well-conducted trial found nothing, why did smaller trials sometimes say otherwise?" Dr. Mann said.

In his review, Dr. Mann analyzed data from 48 studies on job stress and blood pressure, all published in English-language journals from 1982 to 2004. Overall, more than 100,000 people were included in the trials. Dr. Mann found that most studies actually found no relationship between job stress and blood pressure, and that findings were very weak in most of the studies that did report a relationship.

"For example, researchers would sometimes find no overall effect of job stress on blood pressure, but would then report a relationship limited to a small subgroup of the study population," he said.

"The trouble was that if any specific subgroup was particularly susceptible, you'd expect to see that subgroup crop up across studies. None did."

In other studies, the authors would focus on a weak relationship found between blood pressure and one measure of job stress, while ignoring the absence of a relationship with all other job stress measures assessed.

Another flaw? Inexplicably, some studies found that job strain affected diastolic blood pressure the bottom number in a reading but didn't affect the systolic pressure (the top number) at all. In fact, two studies neglected to even mention systolic pressure.

"This is all very odd, since clinicians know that systolic pressure varies more widely than diastolic pressure. It's also a more reliable marker of cardiovascular risk compared to diastolic readings," Dr. Mann says. "The omission of systolic pressure in those studies' data is troubling," he adds.

Finally, most trials that have looked at potential remedies for chronic stress particularly stress reduction techniques found that they did not lower blood pressure levels. "This suggests, of course, that the job stress wasn't causing the hypertension in the first place," Dr. Mann says.

He stressed that he in no way disagrees with the notion that clashes with co-workers can boost blood pressure over the short-term minutes or hours. "Furthermore, reliable studies have shown that ongoing difficulties at work can contribute to coronary artery disease," Dr. Mann adds. "That appears to be true, but blood pressure does not seem to be the link between the two."

So, if the evidence suggests otherwise, why does the idea that job strain is a contributor to high blood pressure persist among researchers, clinicians and the general public?

"Mainly because there is no doubt that stress can elevate blood pressure in the moment. But the corollary that recurring stress leads to sustained blood pressure elevation has not been demonstrated, despite decades of research that aimed to prove it. It's hard not to think that many researchers for a variety of reasons have a vested interest in keeping this notion alive, and that they publish articles that strain to support their view," Dr. Mann says.

"However, as scientists, we need to get better at weeding out faulty data and prove that, in this case at least, the 'emperor has no clothes.'"