An expert at the Ohio State University College of Medicine has shed new light on this connection by reviewing research investigating how stress can wreak havoc on the body.
Psychologist Janice K. Kiecolt-Glaser points out that the field of psychoneuroimmunology (PNI) investigates how stress and negative emotions like depression and anxiety affect a person's health.
Over the last three decades, researchers have uncovered a number of ways that stress adversely affects human health, and specifically, how stress can damage our immune system.
Numerous studies have also shown that stressed individuals show weaker immune responses to vaccines.
Kiecolt-Glaser observes: "The evidence that stress and distress impair vaccine responses has obvious public health relevance because infectious diseases can be so deadly."
The reviewer further highlights the fact that stress and depression have been found to increase the risk of getting infections, and to result in delayed wound healing.
Kiecolt-Glaser says that inflammation is the body's way of removing harmful stimuli, and it also starts the process of healing, via release of a variety of chemicals called proinflammatory cytokines, such as interleukin-6.
However, says the reviewer, too much inflammation can be damaging and has been implicated in the development of many age-related diseases, including Alzheimer's Disease, Parkinson's disease, arthritis, and Type II diabetes.
According to Kiecolt-Glaser, the production of proinflammatory cytokines can increase due to negative emotions and psychological stressors.
It was found in a recent study that men and women, constantly under stress because they served as caregivers to spouses with dementia, had a four times larger annual rate of increase in serum interleukin-6 levels as compared to individuals without caregiving responsibilities.
The changes in interleukin-6 levels among former caregivers did not differ from current caregivers, even following the death of the impaired spouse, indicating that chronic stress might cause the immune system to age quickly.
Kiecolt-Glaser notes: "These stress-related changes in inflammation provide evidence of one mechanism through which stressors may accelerate risk of a host of age-related diseases."
The reviewer stresses the need for taking into account people's environment when studying the link between stress and health.
She says that diets may modify interactions between psychological and immunological responses.
She further points out that environmental toxins like pesticides and air pollutants can have extremely negative effects on the immune system, and these effects may be intensified in stressed individuals, increasing their risk for developing allergies, asthma, and viral infections.
She also says that to most effectively tackle the questions raised by recent PNI research, cross-discipline training needs to be emphasized for students.
According to her, psychology students who gain a strong foundation in areas such as biology and physiology will be able to enter into powerful collaborations with scientists conducting immunology research.
Kiecolt-Glaser feels that the questions answered by these collaborations will advance PNI as well as psychology in general.
"By providing key data on how stressful events and the emotions they evoke get translated into health," she suggested, "psychology will assume a more dominant role in the health sciences, in health promotion, and in public health policy."