Hans Selye's definition of stress and chronic stress effects

Stress refers to a state of tension that the mind and the body are subjected to in response to real or perceived threats. The term stress was originally coined by the Canadian endocrinologist Hans Selye in 1936, who defined stress as "the non-specific response of the body to any demand for change" [AIS] There is no one single definition for the term and a generally accepted definition of stress is "a condition or feeling experienced when a person perceives that demands exceed the personal and social resources the individual is able to mobilize." [AIS] During his experimental studies on animal subjects, Selye noted that exposing animals to irritant and dangerous physical or chemical stimulus (such as heavy noise, glaring light, etc.) resulted in a common spectrum of pathologic response that included stomach ulcerations, adrenalin overload, lymph tissue shrinkage, etc. Selye also coined the term stressors, which refer to the stimuli and proved that prolonged or chronic exposure to stress stimuli resulted in the manifestation of diseases such as arthritis, heart attack, stroke, kidney failure etc. In the test subjects. This finding added a new perspective to the composite etiology of diseases. [AIS] An overview of stress with a brief discussion of stress induced homeostatic mechanisms would help us better understand the subject.

Stress (A subjective experience)

Stressors have varied effects on different people and so stress is regarded as a subjective phenomenon. An interesting example would be the roller coaster ride and how it is perceived differently by different people. While for some the roller coaster would be a joy ride for others it would be a nightmare. [AIS] Though stress is widely regarded as a negative phenomenon, research has shown that stress within a certain threshold is very beneficial and productive for the person. This positive stress is what Selye defined as eustress. [AIS] Participation in a sports meet for instance would create stress but it prepares the body for the event and helps the athlete achieve his peak potential. So moderate levels of stress can be very stimulating. Chronic stress on the otherhand is overwhelming stress, which the adaptive mechanisms of the body cannot handle resulting in total breakdown of the nervous system. Chronic stress is involved in the etiology of a wide variety of diseases and is thought to hasten biological aging.

Chronic Stress

Stress responses or what is called as the adaptive mechanisms, can be both beneficial (in the short run) as well as detrimental. (In the long run) A study by Gregory E. Miller, Ph.D and colleagues from the Washington University compared the effects of chronic stress on immune system. For the study, the researchers compared 25 parents of children undergoing treatment for cancer with 25 healthy parents who served as the control group. After obtaining the initial blood samples, the researchers took periodic salivary cortisol measurements for two days. Results from the study clearly indicated that parents of cancer children had high levels of stress compared to the control group. One important finding of the study was that the parents of the cancer children had lower sensitivity to glucocorticoid hormone, which is involved in the anti-inflammatory mediation process by controlling the production of pro-inflammatory cytokines interleukin-1B, interleukin-6 and tumor necrosis factor. Dr. Miller, the chief researcher of the study says, "These findings suggest a novel mechanism through which psychological stress could influence the onset and/or progression of conditions that involve excessive inflammation, like allergic, autoimmune, cardiovascular, infectious and rheumatologic illnesses," [Gregory E. Miller, 2002]

A more recent study in which Dr. Miller was also a co researcher revealed stress-induced alterations in immunological mechanisms. For this study, the researchers again compared cancer caregivers (high level of stress) with a control group of individuals without such stress. The researchers found that even among the caregivers who had comparable cortisol levels with the control group individuals, there was a distinct change in the immune system response. It was found that gene expression of the monocytes were significantly altered among the caregivers such that they had a reduced response to anti-inflammatory effects of cortisol. They were also found to be more responsive to the pro-inflammatory factor 'kappa B, keeping them in what is known as the 'immunologically activated state'. As Dr. Miller explains, "caregivers have similar cortisol levels as controls, their cells seem to be 'hearing' less of this signal. In other words, something goes awry in caregivers' white blood cells so they are not able to 'receive' the signal from cortisol that tells them to shut down inflammation." [Gregory E. Miller, 2008] The researchers conclude that this stress induced immunologically activated state might predispose them to many diseases such as diabetes, depression and other cardiac conditions.

Several studies have implicated stress in the development of metabolic syndrome (chandola et.al, 2006) and coronary heart diseases (Bunker et.al, 2003). One research studied the relationship between occupational stress and cardiovascular mortality. This longitudinal study observed 812 employees (545 men, 267 women) working at a metal industry in Finland. All the subjects were free of any cardiovascular complications during the baseline test conducted in 1973. Subsequent examinations were conducted at 5 years and 10 years from the baseline examination. The study utilized the 'job strain model' and the 'effort reward imbalance model' to find the association between job related stress and cardiovascular mortality. The national mortality register (1973-2001) was consulted. The study revealed that employees with high job stress as indicated by high demands, lower control had a 2.2 times (95% confidence interval 1.2 to 4.2) higher cardiovascular mortality risk compared to fellow employees with low job related strain. When the data was assessed using the effort reward model, it showed that employees who had effort reward imbalance had a 2.4 times (1.3 to 4.4) increased risk for cardiovascular mortality. The data also revealed higher serum cholesterol levels and BMI levels among stressed employees at 5 and 10-year follow up examinations. These findings strongly suggest that work related stress could be a high risk factor for cardiovascular diseases. [M Kivimaki, 2002]

Stress Management

Since chronic stress and the accumulation of high levels of stress hormones are very dangerous and predispose a person to a wide array of stress induced diseases, it is essential to destress our body and mind regularly. Exercises are considered the first choice treatment in the management of stress and in the control of stress related disorders. A recent study by Duke University medical research center revealed that exercises not only relive depression and distress but also bring about positive changes in important physiological markers of cardiovascular disease. For this study 134 stable cardiac patients were recruited and assigned randomly into three different groups. The exercise group received 35 minutes of aerobic training 3 times a week for 16 weeks while the 'stress management group' received stress management therapy for 1.5 hours once a week for 16 weeks. The third group, which also served as the control group, received only regular pharmacological intervention. At the end of the study period, the researchers conducted ultrasound-imaging study of the brachial artery before and after the application of a tourniquet to record endothelial dialation. The results siuggested that the experimental subjects (both exercise group as well as behavioral therapy group) achieved a 25% improvement in 'flow mediated dialation' compared to the control group that received only medical treatment. James Blumenthal, the lead researcher reported, "To our knowledge, this is the first study to show that stress management might reduce cardiovascular risk in part through beneficial effects on vascular endothelial function," [Blumenthal J, 2005]

Conclusion

Stress is part of our life and there are elaborate coping mechanisms to deal with it. Stress causes various physiological changes in the body, which have to be controlled within a short period of time to restore homeostasis. We are still a long way from understanding with any certainty the biological mechanisms linking stress and diseases, and the reasons why some people handle stress better than others. What we are aware is that a complex interplay of neurotransmitters, hormones, and several modulatory mechanisms are involved both in preparing the body to deal with a stressful situation and in maintaining the homeostasis of the body. However, when these coping mechanisms become stretched for prolonged periods of time we suffer the consequences of stress induced illness. Chronic stress problem should be carefully managed. A combination of regular exercises with behavioral therapy is ideal in the treatment of stress.