Everyday in my medical practice, I see people experiencing health problems generated or worsened by stress.  In her book, The Cure Within, Harvard historian Anne Harrington tells the story of how scientists discovered stress’s harmful effects. 

The story begins with a physiologist named Walter Cannon.  Cannon was using newly developed X-ray technology to study peristalsis—the intestinal movements needed for digestion.   As Harrington writes:

“Cannon found that whenever his experimental animals—mostly cats—became distressed or enraged, their peristaltic activity was inhibited.  This led to new questions:  Why should distress or rage inhibit peristalsis? What did emotions and digestion have to do with each other?

To answer these questions, Cannon agitated cats by having dogs sniff and bark at them.  He then drew blood from the agitated cats and compared it with blood taken cats who had not been threatened.  Cannon found that the blood of the frightened cats contained a chemical adrenin (today called epinephrine or adrenaline).  Injecting adrenin into an animal resulted in higher blood pressure and glucose levels, inhibition of digestion, and dilation of the pupils.  Considering this data, Cannon had the insight that the physiologic changes he noted in the animals he stressed would be useful for either fighting or fleeing from an enemy.  

As Harrington writes, 

“Cannon’s next move was key.  He noted that human beings have the same capacity as other animals for fight or flight reactions;  we too have homeostatic systems to help us regulate the use of these reactions in response to environmental challenges and threats.  In the modern era, however, Cannon suggested that life had become so fast paced, so uncertain, and consequently so anxiety-provoking that many people went through their days as if they were cats faced with dogs perpetually barking at them.  With their ’emergency’ responses thus chronically stimulated, there were few opportunities for homeostatic mechanisms to restore their physiologies to a resting state.

The work of physician and biochemist Hans Selye further advanced our understanding of stress.  Selye was working with other scientists to identify a new female sex hormone.  He injected extract from the ovaries of freshly slaughtered cows into female rats, studying how their bodies responded.  When Selye performed autopsies on “he was disappointed to see there had been no change in their sex organs.  However they did all suffer from a curious triad of symptoms;  peptic ulcers, enlarged adrenal glands; and shrunken immune tissues.”  When Selye injected the extracts of other organs such as kidneys and spleens into the rats, he noticed the same response.  “Then he had a new thought:

Perhaps what the rats were experiencing was not a specific response to a specific agent but a nonspecific response to the trauma of having a noxious substance injected into their bodies.  He began to wonder if other kinds of trauma would result in the same outcome–and experimented by making life very unpleasant for many rats.  Some were put on the roof of the medical buildings in the winter; some were put down in the heat of the boiler room; some underwent an operation in which their eyelids were sewn back and they were exposed to bright lights; some were placed inside barrel-like, revolving treadmills powered by an electric motor that forced them into a state of complete exhaustion.  ‘It gradually turned out,’ he later said, ‘that no matter type of damage I inflicted on an experimental animal, if it survived long enough and the stressor was sufficiently strong, the typical combination would be produced: adrenal hyperactivity, lymphatic atrophy, and peptic ulcers.’ ”  

Selye named the rats’ response to their burdensome conditions “stress” and wondered if it could be behind many of the common, but poorly understood health disorders that occur in humans.  He took his stress theory to a wide variety of audiences, including doctors, the military, and the public at large.  The idea caught on, generating more and more fruitful research into stress’ effects on our bodies.