Any time we're in a situation beyond our control, the brain releases two hormones, cortisol and adrenalin, which allow us to engage our fight-or-flight response - without them, we would not recognize or react to danger. But when a brain is constantly stressed, confronted with a daily onslaught of overwhelming situations, it begins to pump out these hormones in excess, throwing off the body's other systems and overpowering the immune system.
Even people who believe they thrive on stress or accept it as part of their chosen profession have a physical response to it they can't control.
Research has shown that high levels of cortisol and adrenalin change the way the body stores fat, leading to higher rates of obesity, and increase its production of cholesterol and insulin, which cause heart disease and diabetes. They even change us on a cellular level, wearing away the telomeres that protect our chromosomes and causing us to age more rapidly.
These changes aren't reversed when a person decides to slow down. "Once you are a hyper-secreter of cortisol, you always will be," Dr. Lupien says.
In addition to being found in saliva, cortisol can be measured in an individual's hair, where the hormone's build up can be tracked over months. Many scientists believe these diagnostic tools can help predict, and possibly prevent, a range of serious health problems.
Consider this: Last month, two researchers at the University of Western Ontario said they have found that hair samples from men who recently suffered heart attacks showed their cortisol levels were elevated for three months before being hospitalized.
Attempts are being made around the world to uncover how health problems are triggered by the way we work.
Harvard researcher Lisa Berkman recently studied 400 employees at four nursing homes in Boston to examine the impact different types of supervisors can have.
"The stunning thing we found was that managers who scored very low on creativity in managing work-family conflicts had employees who scored much higher in terms of their cardiovascular risk," she says. "They were more likely to have diabetes, they were more likely to have hypertension, they were more likely to be overweight, than people with managers who were more adaptive."
Similarly, the renowned Whitehall Study has tracked 18,000 members of the British civil service since the 1960s, and found that employees' health varies profoundly according to how they are treated. People who have less control over their jobs and feel overextended or without support have a markedly higher incidence of obesity, higher prevalence of underlying illness, higher blood pressure and increased risk of heart disease.
"Your whole lifestyle, everything about your health, is influenced by these worries, anxieties, the lack of a support system in your job, in your life," says Bruce McEwen, a neuroscientist at New York's Rockefeller University who is considered the godfather of stress research. "This is something that has a disproportionate effect on our health-care systems and on our productivity."
STRESS, THE NEW SMOKING?
The problem has become so profound that governments are starting to take notice.
Last month, the U.S. Department of Health and Human Services made stress the focus of its annual campaign to raise awareness of a vital mental-health issue.
And this month, European MPs voted to extend fully paid maternity leave to five months, as a way of easing the burden on young families.
China, meanwhile, has responded to growing concern over public health by reinstating mass calisthenic routines that were launched by Mao in 1951 but dropped in the lead up to the 2008 Olympic Games.
Lisa Raitt, the federal Minister of Labour, is currently doing cross-country public round tables on the issue of mental health and the workplace, and says work-life balance is emerging as a serious problem.
"The worst thing possible is for someone to get so unbalanced that they have to go on long-term disability or take sick days or go to work and just go through the motions," she says. "It is one of the biggest issues we have out there in the workplace."