HealtH eFFects oF stress

IIPart

5.4 HealtH eFFects oF stress

Stress causes mobilisation of the entire organism. When the mechanisms and effects of stress were being discovered in the 1980s, stress was estimated to lead to more than 14,000 physicochemical changes in an organism (Wilson and Schneide, after Asterita 1985). Attempts at summarising these changes are no longer made, because, starting from the molecular level, virtually no aspect of the organism is free from stress-induced changes. Therefore, stress is a risk factor for many diseases of very diverse origins (Johnson 1990; Dallman et al. 2004, 2007; Marmot and Shipley 1996;

Walker et al. 1999; Widerszal-Bazyl 2005; Kreis and Bodeker 2007; Herbert et al.

2006; Jedryka-Góral et al. 2002; Bland et al. 2000; Nilsson 2007).

26S + 1NS

1NS 0 0

500 1000

A (pg/ml) 15002000

2500 3000 3500

5 15

Time (min)

30 5 15

NS

Figure 5.6 Adrenaline concentration in the blood during a 30-minute exposure to novel stress (1NS) and a response to the same event after previous long-term exposure to another stress situation (26S + 1NS). (Reprinted with permission from Konarska, M. 1995. Response of the Sympathetic-Adrenal Medullary System to the Test Stress of the Chronically Stressed Rat.

Habil. Diss. (abstract in English). Warsaw: CIOP.)

96 Handbook of Occupational Safety and Health Epidemiological studies have found a distinct correlation between the stress- inducing factors of life and work and the incidence of the following conditions:

Metabolic disorders (vascular atherosclerosis, obesity, and diabetes).

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Invasive diseases caused by both bacteria and viruses (tuberculosis and

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neoplastic diseases)

Regulatory diseases (hypertension and coronary heart disease)

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Psychological disorders (depression, anxiety, insomnia, and chronic fatigue

•

syndrome)

Under substantial stress, adrenaline and other catecholamines exert a significant influence on the reactivity of the circulatory system by increasing the heart rate and the arterial blood pressure; hyperactivity and a substantial level of variabil- ity in circulatory reactions under chronic stress, particularly in the case of genetic predisposition to hypertension, may become a direct cause for the development of

‘resistant’ hypertension, which is caused by hypertrophy of the blood vessel muscle tissue. The causes of hypertension include changes in the activity of hormones such as angiotensin and renin, which participate in the kidneys’ control of sodium and the volume of bodily fluids.

During long-term stress, corticosteroids influence the concentration of insulin and balance of carbohydrates and lipids, leading to changes that cause metabolic diseases such as obesity, diabetes, and atherosclerosis.

Corticosteroids and catecholamines (mainly adrenaline) activate many metabolic paths through glycogenolysis, causing an increase in the production of coenzyme A molecules (Co-A; one-carbon fragments), which serve as building blocks for the synthesis of endogenous cholesterol.

In the sphere of psychogenic reactions, the role of corticosteroids in the develop- ment of chronic fatigue syndrome, conservation withdrawal reactions, depression, insomnia, and neurodegenerative diseases, such as Alzheimer’s or Parkinson’s dis- ease has been confirmed (Walker 2007; Rydstedt et al. 2007a,b; Dallman et al. 2004, Dallman et al. 2007).

Studies have also confirmed a correlation between the increased secretion of corticosteroids and invasive diseases. Excessive secretion of these hormones leads to reduced immunity due to disturbances in the production of immunological fac- tors like cytokines and antibodies, as well as a decrease in the activity of immune cells (T and B lymphocytes), phagocytes, and other cytotoxic cells. This results in a general decrease in immune system activity (Walker et al. 1999; Jedryka-Góral et al. 2002).

Since the 1980s, studies on the physiological and biomedical stress mechanisms have focused on processes caused by stress at the cellular level, initiated by the discovery of ‘thermal shock proteins’ (HSP family), identified by Alfred Tissiers (1917–2003) after accidental exposure of cells to a high temperature. These proteins appeared in cells in response to stress or diverse toxic factors, such as infections, toxins, hypoxia, and dehydration. The production of thermal shock proteins is a cellular-level reaction to stress, common in all living organisms—plants and animals.

It confirmed the thesis of unity of the entire living world, proposed in the nineteenth

The Physiology of Stress 97 century by Cannon; at the same time, it confirmed the thesis of nonspecific reaction to stress, a component of Selye’s theory that had been criticised for many years.

The discovery of thermal shock proteins has enabled valuable research using simple animal and plant organisms as models, as well as tissue and cell cultures, which has drawn universal conclusions regarding the mechanisms of the emergence (and treatment) of many genetic and metabolic diseases in humans.

The common fruit fly Drosophila melanogaster has contributed to genetics and medicine (such research was awarded a Nobel prize in 1933, for mechanisms of inheritance of qualities, and in 1995, for control of genetic congenital defects) and today serves as a ‘research model’ for studies on the influence of stress on the aging processes. These are manifested by the accelerated shortening of telomeres and apoptosis, that is, programmed cell death—a process, which, when disturbed, leads to the development of neoplasms.

In neurophysiology, studies on protein aggregation in Alzheimer’s and Parkinson’s diseases have been conducted using the nematode Caenorhabditis elegans (such a study was awarded a Nobel Prize in 2006 for the study of control of information flow in the genes). This small, transparent organism has 959 somatic cells and 16,757 genes; about 51% of its genes are identical to those of humans, including those responsible for neurodegenerative processes. The result of this research is of great practical significance, as it will allow the determination of pharmacological methods to stop the basic disease mechanisms that are triggered by stress and other factors.

Many years of research have shown that prolonged stress may also be a signifi- cant risk factor for diseases, across civilisations, just as are genetic factors, age, and individual traits.

For instance, 25 years of socioepidemiological research conducted within the framework of the Whitehall or Workhealth II programmes (projects in the European Union) proved that the long-term effects of stress cause disorders of the circula- tory and immune systems (Marmot and Shipley 1996; Kreis and Bodeker 2007).

The societies of Central and Eastern Europe have been undergoing a process of fast socioeconomic and cultural transformation and have recently served as models for such research. The research shows that the main risk factors include socioeconomic changes resulting in higher levels of stress at work due to increased competitiveness, uncertain employment, and decreased control (Widerszal-Bazyl 2003; Cox et al.

2000). According to forecasts, there will be an epidemic increase in the incidence of diseases of the circulatory system, obesity, and depression; these will be the main causes of early deaths (Siegrist 2001; 2007) until 2020. In Russia, the increase in the death rate since 1989 has already totalled about 400,000 per year (Williams 2007), whereas in Hungary, the mortality of men aged 40–69 has increased from 12.2% to 16.2% (Kopp 2007).

All aspects of research on stress, including biomedical, psychological, and psy- chosocial, have been combined into a single field of research that deals with the biol- ogy of happiness and positive well-being. During a conference on stress in Budapest in 2007, Andrew Streptoe presented the results of a meta-analysis indicating that the death rate in a population of several thousand people dominated by positive emo- tions and pro-health behaviours was lower than the average by almost 19% (Streptoe 2007). These correlations are associated with psychobiological reactions activated by

98 Handbook of Occupational Safety and Health the CNS, including neuroendocrinological, immunological, inflammatory, and circu- latory responses. The results of research in this field underline the need to engage in activities aimed at the promotion and shaping of pro-health behaviours.