Getting stressed now and again may be good for your health, according to new research. But long-term stress can damage the bodyís immune system.
Research by Dr Suzanne Segerstrom and Dr Gregory Miller published in the journal Psychological Bulletin examined some 300 scientific papers on stress involving almost 19,000 people.
They found that a short burst of stress, such as that caused by giving a speech, may strengthen the body's immune system by triggering the immune system-boosting 'fight or flight' instinct that dates back to when early man was threatened by predators.
But long-term stress such as an injury or trauma that caused permanent or life-changing damage, such as having a long term disability, losing a partner or spouse or being abused as a child, appeared to wear out the immune system, leaving people more prone to infections.
The longer that stress persists, the more the immune system is hit by potentially damaging changes. First the defences of individual cells are broken down, and then the broader immune function.
"Stressors with the temporal parameters of the fight-or-flight situations faced by humans' evolutionary ancestors elicited potentially beneficial changes in the immune system,Ē the researchers said.
"The more a stressor deviated from those parameters by becoming more chronic, however, the more components of the immune system were affected in a potentially detrimental way."
The researchers from the University of Kentucky, USA, and University of British Columbia, Canada, also found the immune systems of older people and people who are already ill are more vulnerable to the negative effects of bad stress and more prone to stress-related change.