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The Concept Of Stress
In daily life, the concept of ‘stress’ is frequently used without a precise definition. However, a common meaning of stress is a condition characterized by, for example, a high work pace, complex problem solving, time pressures, or conflicts between different demands, that is, a condition in which one feels that the demands exceed what one can manage.
In scientific research, the concept of ‘stress’ is not only used both as a stimulus and as a response but also as an interaction between the individual and the environment. Responses to stress involve psychological, behavioral, and bodily components. Stress responses can be induced not only by psychological and psychosocial factors but also by physical (noise, heat, cold, vibration) and biological conditions (exhaustion, infections). Human and animal responses to stress have developed during evolution and contributed to adaptation to various environmental conditions. In animals, the evolutionary principles are still very important. In humans today, however, evolution is not supposed to determine life or death; humans try to protect individuals with major handicaps or chronic diseases in order to give all individuals a chance to spread their genes. It has taken millions of years for the present physiological stress systems to evolve. From a human historical perspective, it is obvious that past environmental conditions quite different from the present ones have formed these response patterns. During the last ten thousand years, human living conditions have undergone dramatic changes, which have accelerated in speed in the recent centuries. The increase in the world population, migration, farming, and technological developments are just a few examples of this. From an evolutionary perspective, this is a very short period in which evolution provides no significant influence on the functioning of human bodily systems. Considering that relatively small adjustments of the human body and biological functions through natural selection or mutations would take thousands of years, from a biological perspective, human beings today are very much the same as they were a hundred thousand years ago.
In order to describe under which conditions stress responses may arise, a number of models have been proposed. All of these models have received empirical support in terms of relations to biological markers of stress, for example, stress hormone secretion, but also in terms of prediction of stress-related health outcomes, such as cardiovascular disorders.
According to one model, psychological stress is caused by an imbalance between perceived environmental demands and the individual’s perceived resources to cope with these demands. This means that individual differences in coping abilities and in their interpretation of the situation will determine their stress responses. Based on these appraisal models of stress, not only overstimulation in terms of, for example, a heavy workload or time pressure, but also lack of stimulation can induce imbalance and stress. Understimulation may occur when individuals are unable to use their education, skills, abilities, resources, and experiences. Examples of individuals who may be suffering from this kind of stress are those who are unemployed, retired, on sick-leave, and those who have simple, repetitive, and monotonous work tasks.
Another model of stress, the Cognitive Activation Theory of Stress (CATS), has also been influential. According to the CATS model, stress is defined as ‘a negative expectancy outcome.’ Stress will occur in a threatening or demanding situation when individuals expect that their actions are not likely to eliminate the threat or help in coping with situational demands. In other words, if one believes that any action will lead to failure, ‘hopelessness’ would be experienced whereas if one expects that there is no causal relation between one’s actions and outcome, feelings of ‘helplessness’ would be experienced. In so doing, stress will be reduced only when actions and threats are linked by an individual’s expectancy of a positive response outcome, that is, successful coping.
A third and very well-known model of stress is the Demand-Control Model, which has been used frequently during the last three decades to describe stress in the work environment. According to this model, high demands combined with lack of influence and control will cause high job strain. High demands combined with a high level of control and influence, however, would contribute to an active and stimulating work situation. Lack of social support has been added as a third factor contributing to stress. Social support involves instrumental and emotional help and appreciation from colleagues and managers. The Demand-Control Model was initially developed to identify stress in industrial work and has been found very useful to predict elevated health risks among workers. In some modern work situations, characterized by information handling and informal work conditions, work stress is likely to be induced in a more complex way. In such jobs, the worker has to define the work tasks and set qualitative and quantitative limits for work performance.
Siegrist (2002) developed a more recent occupational stress model, which is known as the Effort-Reward Imbalance (ERI) model. This model is relevant for identifying stress in the modern work environment. According to this model, the employee has formed a contract with the employer, in which both parties have certain expectations. The employee is expected to carry out a specific work task, and the employer is expected to compensate the employee by some kind of reward. The reward is usually monetary but it could also involve career opportunities, appreciation by colleagues and managers, and occupational status. Stress is induced when this contract is broken and the employee’s effort is not adequately rewarded. Characteristics of the employee can also contribute to additional health risks. For example, overcommitted individuals will put increasing effort into their work in order to make sure that they fulfill all possible expectations than those who are not overly committed.
Health Problems In Modern Society
In the beginning of the twentieth century, infectious diseases such as pneumonia, diphtheria, and epidemics were common reasons for death. However, in the industrialized countries today, there has been a shift in the causes of death to diseases with a more complex background, such as cardiovascular disorders and cancer. Myocardial infarctions, stroke, and other cardiovascular diseases cause the death of almost 50% of the population, and various forms of cancer cause the death of about a third of the population. In less developed countries, such as in several countries in Africa, infectious diseases such as acquired immunodeficiency syndrome (AIDS), malaria, diphtheria, and pneumonia are still common causes of death. In these countries, women as well as their infants are also at risk of dying during childbirth.
However, the major health problems affecting the working population in the industrialized countries today are nonfatal disorders with a complex and multifactorial etiology, where stress seems to play an important role. Although these disorders cause absenteeism from work, illness, and an enormous economic societal burden, they may not necessarily increase mortality. For instance, women generally report more health problems than men, but women usually live longer.
In Europe, America, Australia, and in many countries in Asia, musculoskeletal disorders, such as neck, shoulder, and back pain, and various mental illnesses, such as chronic fatigue, burnout syndromes, depression, memory impairment, and sleeping problems, are dominating health problems. In addition, behavioral disorders such as drug addictions (alcohol, narcotics) and eating disorders (obesity, bulimia, anorexia) are important public health problems. Among other frequently reported health problems are headaches, gastrointestinal disorders (e.g., irritable bowel syndrome), infections, and type 2 diabetes.
Socioeconomic Status And Health
A typical feature of these disorders is that social, psychological, and behavioral factors interact with exposure to different physical and social environments (Sapolsky, 1998). Considerable health differentials can be found between as well as within countries since health is closely linked to social position, education, income, and income distribution. The mechanisms behind these relationships have been investigated and discussed extensively, but are not yet fully understood (Marmot, 2004).
The association between socioeconomic status (SES) and health exists in all parts of the world (O¨ stlin, 2004). Individuals with higher education, income, and occupational status are almost always healthier and living longer than individuals with lower education, income, and occupational status. In economically poor countries, lack of medical care, inadequate nutrition, polluted water, sub- standard housing, and poor sanitary conditions are important explanations for these health differentials, but in affluent societies other factors linked to SES, such as relative deprivation, life style behaviors (smoking, alcohol, unhealthy food, lack of exercise, violence, etc.), work conditions, and access to social networks are likely to be more important (Adler et al., 1999). Indeed, understanding the developmental pathways of these various stress-related factors in various communities worldwide could lead to a better understanding of the link between SES and health.
In a recent review summarizing findings on social position and the physiological mediators of the SES– health relationship in different species, Sapolsky (2005) concluded that stress-induced health problems related to social position depend on the stability of the social hierarchy. In relatively stable social hierarchies such as among humans, rats, and mice, where subordinates are exposed to social stressors and low availability of social support, low social rank gives rise to a particular psychophysiological profile. An association based on a reverse causal order is unlikely. Based on his review, psychophysiological profiles of single animals do not predict their subsequent ranks in social groups. In social groups where dominance has to be repeatedly and physically defended (e.g., among male chimpanzees), high social status is associated with elevated physiological arousal and increased risk for adverse health.
Since humans may belong to a number of different hierarchies, social position or rank is more difficult to determine than in animals. For example, an individual in a low-status job or with a low level of education may be a top player in the local football team or receive a lot of prestige as a musician or as a performing artist. In addition, early-experienced SES has been linked to health over time. Parents’ SES seems to influence their children’s health status during childhood as well as adulthood. Thus, describing the physiological mechanisms linking SES to health can be expected to be more complex in humans than in animals. Measures of social position, income, education, and rank in social hierarchies may also differ. Nevertheless, the SES–health associations are very consistent in humans (Marmot, 2004).
Bodily Responses To Stress
Mental stress causes bodily reactions. By signals from the cortex, other centra in the brain, such as thalamus, hypothalamus, and hippocampus, are influenced and, in turn, send signals via nerves, hormones, and/or the immune system to other centra and, eventually, to all parts of the body. These bodily responses include the cardiovascular, the immune, and the gastrointestinal systems, the muscles, sleep, and healing processes, to name only a few. Via feedback mechanisms, the brain is informed about these bodily responses and thus regulates various systems in order to keep, for example, an adequate heart rate or blood pressure. However, under certain conditions, such as under chronic stress, these regulatory mechanisms might fail and initiate vicious circle processes through which inadequate or exaggerated responses will contribute to negative health outcomes. For example, an increase in heart rate due to stress may enhance the individual’s perception of stress and thus induce an additional increase in heart rate, as well as other biological changes. Two neuroendocrine systems are of particular importance in coping with stressful conditions: the sympathetic adrenal medullary system (SAM) and the hypothalamic pituitary adrenocortical (HPA) axis.
The SAM system is activated by sympathetic nerve stimulation from the hypothalamus. It stimulates the adrenal medulla to secrete the two catecholamines epinephrine and norepinephrine into the blood stream. Elevated epinephrine levels in the blood will increase heart rate, cause vasodilation of the arteries in the muscles and the brain, and stimulate lipolysis, that is, the release of energy in terms of glucose and lipids into the blood. Norepinephrine is also a transmitter substance in the sympathetic nervous system. During activation of this system, norepinephrine will be released into the blood from sympathetic nerve endings. It is important to mention that it also has an important role in controlling blood pressure homeostasis by vasoconstriction of the blood vessels. During stress, vasoconstriction of the blood vessels will cause a redistribution of blood from the gastrointestinal system and the skin to the muscles and the brain, as well as contribute to an increased supply of energy and oxygen to the cells. This will happen in less than a minute after stress exposure, and this energy mobilization will increase the individual’s possibilities to survive by fight and flight in a threatening situation. Both, epinephrine and norepinephrine can be measured in blood and in urine.
The HPA axis is also activated by signals from the cortex. By means of the hypothalamus and hippocampal formation, the pituitary is affected by hormonal signals (corticotropin releasing factor, CRF) and responds by increasing the secretion of ACTH (adrenocorticotropin hormone). Through the blood stream, ACTH will stimulate the adrenal cortex to secrete cortisol. It takes about 30 min after exposure to a stressful situation for the cortisol level to reach its peak. Cortisol affects the metabolism in the cells and has an important role in controlling the immune system (antiinflammatory effects). Moreover, this system prepares the organism for sustained stress exposure. Cortisol can be measured in blood, urine, and saliva.
In an acute stress situation, for example, in response to a sudden physical threat, the elevated levels of stress hormones will start a series of bodily responses. There is an increase in heart rate and blood pressure and a rapid release of energy from the liver in terms of glucose and lipids into the blood stream, metabolic activity is attenuated (decreased salivary production and gastrointestinal activity), reproductive activity is reduced (decreased secretion of sex hormones), and some of the immune functions are activated during an acute stress response. In addition, pain sensitivity is reduced, pupils are dilated, concentration will narrow in on the immediate threat (tunnel vision), and certain memory systems will be strengthened. As a result, more energy to the muscles and the brain will increase physical and mental capacity. Reduced pain sensitivity will make the individual capable to continue to fight or run, even in the case of tissue damage, and increased coagulation will reduce bleeding. By remembering under which circumstances the threat appeared, the individual will also have a better chance to avoid similar threats in the future. In conclusion, this well-orchestrated series of actions in various systems will increase the individual’s mental and physical resources to cope with an acute physical threat, but it is less adequate or may even be harmful during mentally induced stress. In addition, the responses to chronic or long-term stress may be quite different, and sometimes even the opposite series of actions can occur. Chronic stress may cause increased pain sensitivity and impaired immune and memory functions. During chronic stress, activity in the HPA axis is particularly important.
Stress As A Health-Promoting Or Health-Damaging Factor
In modern society, exposure to mental and psychosocial stress is probably more common than exposure to physical threats. Under conditions of psychological stress, an increase in heart rate, blood pressure, and blood lipid levels may be more harmful than protective. For example, it has been reported that psychological strain contributes to cardiovascular disorders. In addition, psychosocial stress conditions in terms of economic difficulties, relational problems, unemployment or threat of unemployment, unsatisfactory working conditions, to name a few, are usually more long-lasting than physical threats or demands. In response to physically exhausting work, it is possible to take a break in order to rest and recover, whereas psychosocial problems exist steadily over time and may influence the individual continuously. Today, just as psychological stress exposure is more common than physical threats, individuals are more likely to experience long-term or chronic stress induced by psychosocial conditions rather than by physical demands or threats.
In ancient times, it is likely that acute threats to survival, induced by confrontations with dangerous animals, human enemies, hunting, extreme weather conditions, and so forth, were the dominating sources of stress. Between these acute stress episodes and moments with sufficient access to food, it is possible that individuals had more time to sleep, rest, and recover. Lack of artificial light also made it necessary to be inactive or sleep during a large part of the day. Although human beings are rather resistant and can survive under long-term stressful conditions, there is likely to be an upper limit for each individual beyond which stress-related symptoms start to appear. For long-term health and survival, an adequate balance is necessary between energy mobilization and rest and recovery. As pointed out by Sapolsky (1998), animals living in their natural habitats, such as zebras on the savannah, are unlikely to develop stress-related disorders. He explains that animals do not spend time on rumination after a stressful event by thinking about what could have happened if they had not escaped from a lion or another predator. Animals are also less likely to anticipate and become stressed by possible future threats. As a consequence, after an acute stressful event, animals will unwind rapidly and change from catabolic (energy mobilization) to anabolic processes, such as eating, digesting, healing, mating, and sleeping.
In order to describe when stress responses are health protective versus health damaging, McEwen (1998) and others have proposed the Allostatic Load Model. Allostasis refers to bodily responses necessary for adjustment, protection, and survival. An adequate economic and healthy response to acute stress exposure means a rapid activation of the allostatic systems in order to cope with the stressor and, at the end of the stress exposure, a rapid return to baseline in order to be able to rest and recover. According to the Allostatic Load Model, health problems may be caused by too frequent activation of the allostatic systems or by an inability to shut off these responses. Also an inadequate (blunted) response, due to dysregulation or exhaustion of a system, may cause health problems because an inability to mobilize resources by one system may cause compensatory overactivation of other systems.
Sympathetic arousal is considered to reflect an active ‘defense reaction’ (fight-or-flight), whereas activation of the HPA axis is representing a ‘defeat reaction.’ In species living in relatively stable social hierarchies, subordination has been linked to activation of the HPA axis (secretion of cortisol or hydrocortisone in primates and corticosterone in rodents) (Sapolsky, 2005). It has been suggested that the HPA axis is influenced by social position even in humans, where the SAM system is involved, too (Cohen et al., 2006). Such findings, however, are not consistent (Kristenson et al., 2004).
In conclusion, the physiological stress systems have evolved due to their protective role in human and animal development. These systems are also necessary for survival today, but as indicated above, the threats and demands of modern society can be quite different from conditions that faced our ancestors. The mobilization of energy induced by the bodily responses to stress will enhance resources for ‘fight or flight,’ but is less adequate in situations requiring mental problem solving or an ability to deal with conflicting information, to name only a few.
Sympathetic activation involves elevated blood pressure and heart rate, and increased cholesterol levels. Sustained sympathetic activation is considered to contribute to coronary heart disease. Dysregulation or hyperactivity of the HPA axis contributes to a number of health problems, such as coronary heart disease, type 2 diabetes, reduced immune function, and memory impairment.
An association between stress and coronary heart disease has been demonstrated in a number of studies. In the 1970s, men characterized by the stress-related type
A behavioral pattern, that is, time urgency, impatience, hostility, and competitiveness, were found to be at significantly greater risk of developing a myocardial infarction compared to their more relaxed type B counterparts, independent of other physical risk factors such as hypertension, blood lipid levels, cigarette smoking, and diabetes. Type A individuals have also been found to respond to stress with more elevated stress hormones and cardiovascular responses. Work stress as measured by the Demand-Control Model or the Effort-Reward Imbalance Model has also been linked to cardiovascular illness in prospective studies (Siegrist, 2002).
The mechanisms linking psychosocial stress and behavior to cardiovascular disorders, such as myocardial infarction, have been investigated extensively. The following series of events has been suggested:
- Psychosocial stress will cause an increase in blood pressure and heart rate, as well as a release of energy in terms of glucose and free fatty acids into the blood stream.
- Frequent or chronic elevation of the blood pressure will contribute to structural changes in the arteries, for example in the coronaries supplying blood to the heart itself (myocardium).
- High blood pressure will lead to thicker and stiffer walls of the blood vessels and a smaller diameter (lumen) will reduce the blood flow, which will, due to higher vascular resistance, increase the blood pressure even more.
- A high heart rate and elevated blood pressure may cause damage to the inner walls (endothelium) of the blood vessels, particularly where a vessel branches off.
- Fatty acids will be built into the walls at these places on the blood vessels and form foam cells in the intima (atherosclerosis).
- The high level of blood lipids during stress will enhance the atherosclerotic process.
- A narrowing of the coronary arteries due to thicker walls and atherosclerosis will reduce the blood to the myocardium. The individual will feel pain (angina) when exposed to physical and mental effort requiring more energy and oxygen to the heart.
- Blood clotting (coagulation) increases during stress and will in combination with atherosclerosis further increase the risk of a myocardial infarction, that is, a complete obstruction of the blood flow to parts of the heart muscle.
- Furthermore, atherosclerotic arteries have been found to respond paradoxically to stressful demands by vasoconstriction rather than by vasodilation (Harris and Matthews, 2004).
Behavioral factors influenced by stress, such as unhealthy food habits (fast food, lack of vegetables and fruit), sedentary behavior, cigarette smoking, and alcohol abuse, will contribute to cardiovascular risk and to the metabolic syndrome (see below).
Early stress exposure and responsivity to stress may determine the function of the stress systems later in life as illustrated in animal studies (Adler et al., 1999). It has also been found that elevated blood pressure reactivity at the age of 20 may predict increased risk of hypertension 20 years later.
High cortisol levels cause an accumulation of fat in the central parts of the body, due to the high density of cortisol receptors on the fat cells. In addition, cortisol contributes to a decrease in the secretion of anabolic hormones, such as sex and growth hormones, which reduces muscle mass in men and contributes to fat distribution from hips and buttocks to the abdominal region (visceral fat) in women. This visceral fat is rich in energy, and free fatty acids are readily released into the blood. In heavy physical work this resource supports the muscles with energy, but in response to psychosocial stress the same release of lipids into the blood increases the atherosclerotic process. Patients suffering from Cushing’s syndrome, a condition caused by very high cortisol levels, demonstrate all these effects in a dramatic way. However, similar but less extreme effects can be seen in individuals exposed to long-term stress. By reducing cortisol levels, some of these processes can be reversed. It has also been suggested that cortisol mediates the effect of the intra-uterine environment on adult circulatory disease, but the evidence is contradictory.
Overactivity of the HPA axis causes insulin resistance and thus contributes to type 2 diabetes. The body responds with increased insulin secretion, which may not be enough to compensate for this effect. Consequently, the cells’ uptake of glucose from the blood will be reduced and they will lack energy. The combination of high blood pressure, high lipid levels, and abdominal fat is commonly referred to as the metabolic syndrome (Grundy et al., 2005), which is linked to cardiovascular disease as well as to type 2 diabetes. Life style factors such as cigarette smoking, a high-fat diet, and sedentary behaviors are also associated with this syndrome.
An additional consequence of long-term stress and chronic overactivity of the HPA axis is impairment of the immune system, with increased risk of infections and delayed healing processes. Cohen (2005) has performed a series of controlled experiments in order to demonstrate how susceptibility to the common cold increases with the amount of chronic psychosocial stress in a dose–response fashion, and that this association is mediated by impaired immune functions. It has also been shown that chronic stress and depression contribute to a more rapid deterioration of the immune system of HIV patients, reducing the time before AIDS develops. Social support seems to have the opposite effect. It not only increases the time before AIDS develops but also reduces the risk of viral infection irrespective of stress level (Cohen, 2005).
Cortisol serves as a reliable marker of HPA activity in humans. Measurements from saliva, in particular, have several advantages as they reflect plasma levels and contain free (active) cortisol where the concentration is unrelated to saliva flow. Another benefit is that samples can be stored at room temperature for up to three weeks. Saliva samples are also easy to collect without interfering with the participants’ normal environment or causing any pain or discomfort. The cortisol-awakening response and the difference between morning and evening levels seem to be of particular importance. Chronic stress and depression have been found to be associated with a flatter diurnal curve, attenuated responses to stress, and elevated baseline levels. High SES and psychological well-being seem to reduce HPA activity (Ryff et al., 2004), but the results are inconsistent. Specific conditions such as burnout syndromes and posttraumatic stress disorders have been found to be associated with suppressed cortisol levels.
The role of stress in gastrointestinal disorders such as irritable bowel syndrome and ulcers has been discussed for a long time. When a bacterium, Helicobacter pylori, was found to be responsible for the development of stomach ulcers, the role of stress in this disorder was questioned. However, most do not develop ulcers despite the fact that they have this bacterium, and some individuals develop ulcers without Helicobacter pylori. According to Sapolsky (1998), the gastrointestinal system (saliva production, stomach function, and intestinal activity) is not prepared to digest food after a period of stress because the mucous membrane in the stomach is thinner. The release of hydrochloric acid in response to food intake is therefore likely to damage the inner walls of the stomach and give the helicobacter a chance to invade the stomach wall.
Memory impairment (episodic memory) is also caused by high cortisol levels due to a breakdown of the dendrite connections between the neurons of the hippocampal formation in the brain. By reducing cortisol levels, these connections are reestablished and memory functions can be restored.
Despite considerable improvements of the physical work environment such as less heavy lifting and better ergonomic conditions, musculoskeletal disorders (MSD) remain a major health problem and constitute one of the most important reasons for long-term sick leave from work. In addition, neck, shoulder, and back pain are common not only in heavy physical work but also in jobs requiring very little physical strength but which may be psychologically stressful, such as work at a computer and light assembly work. This indicates that other factors, such as mental and psychosocial stress, are likely to play an important role in these disorders, a notion that is supported by epidemiological studies showing that work stress may predict MSD. In order to explain how long-term but low muscular activity may develop into muscular pain problems, a number of different models have been proposed (Lundberg and Melin, 2002). One of these models, the Cinderella Hypothesis, is based on an orderly recruitment of motor units in the trapezius muscle, covering the neck, shoulders and upper part of the back, in response to increased muscular force. At low levels of force, motor units with low thresholds are activated first and remain activated until complete relaxation of the muscle. Under long-term and low levels of muscle activity, these motor units may become exhausted and various degenerative processes may start that eventually lead to pain conditions. Recently, it has been demonstrated that mental stress may activate the same motor units as physical demands and, consequently, it may keep these low threshold motor units active even in the absence of biomechanical work. As mental and psychosocial stress can be long-lasting, this may be an important factor for the development of muscle pain in psychologically stressful but physically light work. Additional reasons for the development of muscle pain due to psychological stress are the lack of time for healing of damaged muscle fibers that are constantly active and the lack of adequate signals of fatigue when very little muscular capacity is used. Under such conditions, the individual may continue to work until a chronic pain syndrome develops, without any awareness of motor unit exhaustion.
Muscle pain associated with psychological factors at the workplace can be explained by a blocking of pauses in muscle activity unrelated to the actual biomechanical work being performed. This will reduce restitution and contribute to sustained activity in low-threshold motor units. This is consistent with data showing that women unable to relax during breaks at work, and women with few ‘EMG-gaps,’ were more likely to develop pain syndromes (trapezius myalgia) during their first year in a new job involving repetitive tasks than their counterparts in the workplace (Veiersted et al., 1993).
Additional explanatory models for stress-induced muscle pain are based on the following:
- the effects of stress-induced hyperventilation on blood pH-levels (alkalosis) leading to muscle tension and increased sensitivity to stress hormones;
- the interaction between nerves and stretching of blood vessels in the muscle, contributing to the secretion of substances increasing pain sensitivity;
- stress-induced dysfunction of the muscle spindles regulating muscle force and coordination of movements, which may start a vicious circle of successively increased muscle tension and an accumulation of pain-inducing substances.
Because the responses to stress are part of a dynamic process, single measures showing high or low levels of stress hormones are usually not sufficient to identify health risks. Chronic stress seems to change the regulation of various physiological processes rather than causing high or low activity in specific systems. This could happen due to excessive and/or long-term stress hormone secretion, combined with high or low regulation of receptor sensitivity.
Whereas some disorders, such as hypertension, atherosclerosis, hyperlipidemia, and diabetes, can be diagnosed reliably by medical examinations and laboratory tests, a large number of disorders, termed as subjective health complaints or medically unexplained symptoms, cannot be objectively confirmed. Muscular pains, stomach discomfort, headaches, and various psychological problems (depression, chronic fatigue, burnout syndrome, sleep problems) can only be measured by self-reports. Similarly, in medical examinations of these disorders, the physician has to make the diagnosis on the basis of the patient’s subjective reports. These disorders usually have a multifactorial etiology and represent the most common reasons for absence due to sickness from work. Stress is assumed to play an important role in the development of subjective health complaints.
Gender Differences In Stress-Related Health
Women generally report more health problems, seek more medical care, and use more medication than men. Yet women usually live longer, which may seem like a health paradox. It is important to mention that gender differences in longevity vary between countries. The most pronounced gender difference, of about 13 years, is seen in Russia. In other European countries and in North America, the corresponding gender differences vary between four and eight years. In poor countries, where women are at great risk of dying during childbirth, there are smaller or no gender differences in longevity, and in some countries, men may even live longer than women. The ‘health paradox’ in most countries may be due to other reasons than the nonfatal health problems affecting people in daily life.
In industrialized countries in Europe and North America, men’s shorter life span is due to a number of factors, such as life style, work conditions, risk behaviors, and biological factors, many of which are stress-related. Women usually eat healthier food, exercise more, and less often drink excessive amounts of alcohol. Cigarette smoking has, until recently, been more common among men than among women, and continues to be the case in many countries. However, in Europe and North America smoking has decreased among men and increased (or remained common) among women, which is reflected in an increasing incidence of death from lung cancer among women. On the other hand, men are still dying from lung cancer and cardiovascular disorders due to decades of cigarette smoking. With regard to work conditions, men are more often exposed to hazardous conditions at the job whereas fatal accidents at work are rather unusual among women. In addition, men more often expose themselves to various risks and neglect to use protective means or follow proper safety instructions for dangerous equipment, not only at work but also in traffic. As a consequence, men die more often than women due to accidents, particularly in car and motorcycle accidents. Men also commit suicide more often than women, although suicide attempts are more common among women. Compared with men, women also seem to be more attentive to minor symptoms. Combined with seeking medical care and the more frequent use of medication, this may protect women from more serious diseases. However, another important explanation for why men die earlier than women is gender differences in age when cardiovascular diseases appear. Although women die of myocardial infarctions, strokes, or other cardiovascular disorders about as often as do men, they seem to be somewhat protected before menopause. Specifically, before the age of 50, myocardial infarctions are 3–4 times more common among men than women. After menopause, when women’s estrogen production ceases, their risk of cardiovascular diseases increases and, consequently, they often contract and die due to cardiovascular diseases when they are older than do men.
With regard to gender differences in nonfatal health problems, a number of factors are likely to contribute, such as biological factors, violence, and work conditions. From a stress perspective, gender differences in type of job and work tasks, as well as in total workload, may be of importance for health. Women and men often have different types of jobs and even when they have the same job they often do different tasks. For example, as physicians, women are often working within emotionally demanding specialties, such as geriatrics and psychiatry, where patients remain for long periods of time because they recover slowly or not at all, whereas men work within surgery and cardiology, where treatment usually is more efficient and rapid and the long-term emotional load therefore is likely to be less pronounced.
Women more often than men are performing repetitive tasks, which are associated with lack of unwinding after work and with health problems such as upper extremity disorders. As lack of rest and recovery seems to be an important health risk, these findings seem relevant for gender differences in health. Occupations dominated by women are also often characterized by low control and lack of autonomy, which according to the Demand-Control Model are likely to induce job strain and health problems.
With regard to total workload, unpaid work from household duties and child care may in some cases contribute to work overload and lack of opportunities for rest and recovery, a situation which is more common for women than for men. Despite women’s equal participation in the paid work force, women still carry the primary responsibility for child care and other unpaid duties at home. Consequently, the total workload (sum of paid and unpaid work) of full-time-employed women is greater than that of men, particularly in families with children.
Women’s employment per se is generally associated with positive health consequences, but there may be a limit at which the combined load from paid and unpaid work responsibilities becomes a health problem. For example, in a recent study comparing paid and unpaid workload in matched groups of full-time-employed men and women, it was found that more women than men had a total workload exceeding 80 hours per week and that women reported more conflicts between paid and unpaid work. Also in these matched groups, women reported significantly more symptoms than men. In recent years, the prevalence of stress-related health problems has increased dramatically in many industrialized countries and the gender differences have become even more pronounced.
In order to compare stress and work conditions in men and women, several studies have been performed on fulltime-employed and highly educated women and men matched for age, occupation, education, and number of children (Lundberg, 2002). Measurements of stress levels during and after work show that there are no pronounced gender differences during work. However, men generally unwind rapidly at the end of the work day, whereas women’s physiological stress levels remain high for hours after work. Both women and men report a peak total workload between 35 and 40 years of age. As would be expected, the number of children at home was found to be of considerable importance for the total workload in terms of hours per week. In families with no children at home, the total workload was about the same, that is, a little more than 60 hours per week. However, in families with three or more children, women’s total workload was almost 90 hours and men’s total workload was about 70 hours. The conflict between demands increased and the control over household work decreased with an increase in number of children at home.
In families with small children at home, the number of extra hours in paid work (overtime) has been associated with elevated epinephrine levels during weekends in women but not in men. Moreover, women who regularly work more than 50 hours per week were found to have twice as high cortisol levels in the morning during the weekend compared with women working fewer hours. In a study of 600 000 male and 400 000 female workers it was found that overtime at work (10 hours or more per week) was associated with elevated risk of myocardial infarction during a one year follow-up for women but not for men. However, in a study of telework among women and men, it was found that men had significantly higher epinephrine levels than women in the evening after working from the home but not when working at the office, indicating that men continued to work in the evening when working from the home.
The influence of mental stress on women’s muscular tension seems to be enhanced in repetitive physical work. Jobs combining mental and physical demands, for example, data entry and assembly work, which are often held by women, may in turn form a particular risk for the development of neck and shoulder disorders. Although biomechanical factors and mental stress seem to contribute to muscle tension in both men and women, lack of influence over the work–rest balance, repetitive work tasks, and unpaid work responsibilities may contribute to keep women’s stress levels and muscle tension elevated off the job as well. Furthermore, women generally report more sleeping problems than men. As sleep is the most important form of rest, where many important anabolic processes are activated, lack of sleep may contribute to the allostatic load in women.
Research indicates that the stress of employed women is determined by an interaction between conditions at work and conditions at home, whereas men respond more selectively to the specific stress situations at work. Men’s stress levels seem to be determined by their actual stress exposure at work, which means that they are better able to relax compared with women when they come home in the evening and during weekends. The most stress-inducing factors may consist of the anticipation of future commitments and events. This is consistent with the fact that stress from paid and unpaid work interacts more for women than for men and that women’s occupational stress may not always be seen in terms of elevated physiological stress levels at work, but may just as well be reflected in elevated physiological arousal at home. Indeed, total workload, role conflicts, responsibilities, and family issues influence women’s life and stress responses in a complex way.
In conclusion, the different roles occupied by men and women are likely to have negative as well as positive health consequences. Work overload and role conflicts are assumed to add to the ‘wear and tear’ of the organism according to the Allostatic Load Model. However, occupying different roles may also increase social and economic status and serve as a buffer against stress-related ill health. Yet, one role may also ‘spill over’ into other roles. Therefore, public health efforts to improve health gaps between men and women need to incorporate both family and work life.
There are considerable individual differences in sensitivity to stress exposure. Although an overwhelming amount of research has been focused on psychosocial factors contributing to ill health, some studies have been performed in order to investigate factors contributing to good health and protection against stress. Social support and high social status are examples of factors known to protect against stress-related disorders.
Ryff et al. (2004) have identified six factors contributing to ‘positive health’ or ‘psychological well-being’: self-acceptance, positive relations with others, autonomy, environmental mastery, personal growth, and purpose in life.
These factors are measured by the Ryff Psychological Well-Being Scale. High scores on this scale are associated with physical and mental health, longevity, and a buffer against stressful life events. As mentioned above, psychological well-being has also been linked to biological markers.
Sense of coherence (SOC) is another concept used to describe factors contributing to good health. Conceptually, it includes perceptions of the environment as structured, predictable, and understandable. A well-known instrument measuring dimensions of manageability, meaningfulness, and comprehensibility has been developed for measuring SOC. In recent studies, it has been shown that women with high SOC have lower systolic blood pressure, better lipid profiles, and lower allostatic load.
Stress is a major health problem in most industrialized countries today. Part of the population seems to suffer from stress induced by work overload, time pressures, and too much responsibility, whereas another part of the population is suffering from stress induced by unemployment, economic problems, and understimulation. Whatever the underlying cause, stress influences various bodily functions that are at times health protective and at others health damaging. Short-term stress exposure is usually not a health risk, whereas long-term stress exposure, even on a low level, may contribute to symptoms by influencing various bodily organs and functions. Stress may also influence health indirectly by various risk behaviors such as unhealthy food habits, lack of physical exercise, cigarette smoking, drug abuse, accidents, and suicide.
By definition, stress means activation of physiological systems and mobilization of energy, that is, a catabolic response, which in the long run has to be balanced by anabolic processes. The human body is rather robust and may be activated rather frequently, intensely, and for long periods of time without health problems. However, sooner or later, these processes have to be replaced by anabolic processes, such as digestion, healing, rest, and reproduction. The long-term balance between catabolic and anabolic processes becomes critical for health. Research indicates that women and individuals in low-status positions are at particular risk of stress-related disorders. Today, it is possible that lack of relaxation is an even more important health problem than the absolute level of mental and physical stress exposure.
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