Researchers conducted an interesting experiment 🔬: they gave subjects nasal drops 👃💧 that contained a common "cold" virus 🤧 or a placebo solution 💊 and then quarantined them 🚪 to check for infection 🦠 and cold symptoms 🤒. Before the nasal drops were administered 💉, the subjects had filled out questionnaires 📝 to assess their stress 😰. Of these subjects, 47% of those with high stress 📈😟 and 27% of those with low stress 📉🙂 developed colds 🤧.
Other studies 📚 have produced two related findings 🔍. First, people who are under chronic, severe stress ⏳😖 are especially vulnerable to infection 🦠. Second, people who show high reactivity ⚡ to stress are at greater risk ⚠️ to respiratory infections 😮💨 when stressed than less reactive people. What is it about stress that leads to illness ❓🤒
The causal sequence between stress and illness 🔄 can involve either of two routes: (1) a direct route ➡️, resulting from the changes stress produces in the body's physiology 🧬, or (2) an indirect route ↪️, affecting health through the person's behavior 🧍♂️. Let's look first at the behavioral route 👇.
Stress, Behavior and Illness 🧠➡️🤒
Stress 😰 can affect behavior 🧍♀️, which, in turn, can lead to illness 🤧 or worsen an existing condition ⚠️. We can see the behavioral links 🔗 between stress and illness 🤒 in many stressful situations 😵, such as when a family undergoes a divorce 💔👨👩👧. In many cases during the first year ⏱️ following the separation, the parent who has the children 👩👧 is less available and responsive 💬❌ to them than she or he was before—a situation described as "diminished parenting" 🚸. Behavioral changes 🔄 during stressful times ⏳😟 often make conditions for all family members 👨👩👧 less healthful 🥗❌, with haphazard meals 🍔, less regular bedtimes 🌙❌, delays in getting medical attention 🏥⏳, and failures to follow physician's recommendations 🧑⚕️❌, for example.
Research 📚 has shown that people who experience high levels of stress 📈😰 tend to perform behaviors that increase their chances of becoming ill 🤒 or injured 🤕. For instance, they consume more alcohol 🍺, cigarettes 🚬, and coffee ☕ than people who experience less stress 🙂. Consumption of these substances ⚠️ has been associated with the development of various illnesses 🦠. In addition, behavioral factors 🧠, such as alcohol use 🍺 and carelessness 😵, probably play a role in the relatively high accident rates 🚗💥 of people under stress 😰. Studies 📊 have found that children 👶 and adults 🧑 who experience high levels of stress 📈 are more likely to suffer accidental injuries 🤕 at home 🏠, in sports activities 🏃♂️, on the job 🏭, and while driving a car 🚘 than individuals under less stress 📉🙂.
Stress, Physiology and Illness 🧬🤒
Stress 😰 produces many physiological changes 🔄 in the body 🧍♂️ that can affect health 🏥, especially when stress is chronic ⏳ and severe ⚠️. In one of our previous lectures 📘, we discussed the concept of allostatic load ⚖️ in which the strain involved in adapting repeatedly 🔁 to intense stressors 😖 produces wear and tear 🛠️ on body systems 🧠❤️ that accumulate over time ⏱️ and lead to illness 🤒. Clear connections 🔗 have been found between illness 🤧 and the degree of reactivity ⚡ people show in their cardiovascular ❤️, endocrine 🧪, and immune 🛡️ systems when stressed 😰.
Cardiovascular System Reactivity and Illness ❤️⚡
Cardiovascular reactivity ❤️⚡ includes any physiological change 🔄 that occurs in the heart ❤️, blood vessels 🩸, and blood 🩸 in response to stressors 😰.
Research 📚 has demonstrated links 🔗 between chronically high cardiovascular reactivity 📈❤️ and the development of CHD 💔 and hypertension ⬆️🩸. For example, high levels of job stress 💼😵 are associated with high blood pressure ⬆️ and abnormally enlarged hearts ❤️📏, and people's laboratory reactivity 🔬 to stress in early adulthood 👶➡️🧑 is associated with their later development of high blood pressure ⬆️. The heightened blood pressure reactivity ⚡🩸 that people display in laboratory tests 🧪 appears to reflect their reactivity in daily life 🌍.
Stress 😰 produces several cardiovascular changes ❤️ that relate to the development of CHD 💔. For instance, the blood 🩸 of people who are under stress 😟 contains high concentrations of activated platelets ⚠️ and unfavorable levels of lipids 🧈, such as cholesterol 🧬. These changes in blood composition 🩸 tend to promote atherosclerosis 🧱—the growth of plaques 🧈 (fatty patches) on artery walls 🩸.
As these plaques build up 📈, they narrow and harden the arteries 🩸🧱, thereby increasing blood pressure ⬆️ and the likelihood of a heart attack ❤️💥 or stroke 🧠💥. Prospective studies 📊 have found that people who display high cardiovascular reactivity ⚡❤️ to stressors 😰 show faster progression 🚀 of atherosclerosis than those with lower reactivity 📉, especially if they experience chronic, severe stress ⏳⚠️ in their lives.
Endocrine System Reactivity and Illness 🧪😰
Part of reactivity ⚡ involves activation of the hypothalamus—pituitary—adrenal axis 🧠➡️🧪, which releases endocrine hormones 🧬—particularly catecholamines ⚡ and corticosteroids 💊—during stress 😰. The increased endocrine reactivity 📈 that people display in these tests 🧪 appears to reflect their reactivity in daily life 🌍. One way in which high levels ⬆️ of these hormones 🧬 can lead to illness 🤒 involves their effects on the cardiovascular system ❤️. For example, an intense episode of stress 😖 with extremely high levels ⬆️ of these hormones can cause the heart ❤️ to beat inconsistently ⚠️ and may lead to sudden death ☠️. In addition, chronically high levels ⏳ of catecholamines ⚡ and corticosteroids 💊 appear to increase atherosclerosis 🧱.
Stephen Manuck 👨🔬 and his colleagues 🧪 have demonstrated this link 🔗 between stress and atherosclerosis in research with monkeys 🐒. In one study, some of the subjects were relocated periodically to different living groups, thereby requiring stressful social and psychological adjustments to retain their dominant social status: the remaining subjects stayed in stable groups. Regardless of whether the monkeys' diets 🍽️ had high or low levels of cholesterol, the stressed subjects 😰 who had to retain their dominant status developed greater atherosclerosis 🧱 than the subjects in the low stress condition 😌. This effect of stress is probably very similar in humans 🧍♂️. Disruptions of soldiers' social status in boot camp affect endocrine reactivity. And as we saw earlier, people with chronically high stress are more likely to develop atherosclerosis than those with less stress. But social support 👥❤️ may help: people with high levels of social support tend to exhibit lower endocrine reactivity ⚡ than people with less support.
Immune System Reactivity and Illness 🛡️🤒
The release of catecholamines ⚡ and corticosteroids 💊 during arousal affects health in another way: some of these hormones impair the functioning of the immune system 🛡️. For example, increases in cortisol and epinephrine are associated with decreased activity of T cells 🧬 and B cells 🧬 against antigens. This decrease in lymphocyte activity 🦠❌ appears to be important in the development and progression of a variety of infectious diseases 🤧 and cancer 🎗️. Among women diagnosed with breast cancer, those with high levels of killer-T-cell activity exhibit less spread of the cancer to surrounding tissue than those with low levels of lymphocyte activity.
Immune processes also protect the body 🛡️ against cancers that result from excessive exposure to harmful chemical or physical agents called carcinogens ☢️, which include radiation ☢️ (nuclear, X, and ultraviolet types), tobacco tars 🚬, and asbestos. Carcinogens can damage the DNA 🧬 in body cells, which may then develop into mutant cells and spread.
When mutant cells develop, the immune system 🛡️ attacks them with killer T cells. Actually, the body begins to defend itself against cancer even before a cell mutates by using enzymes to destroy chemical carcinogens or to repair damaged DNA 🧬🔧. Research has shown that high levels of stress 😰, however, reduce the production of these enzymes ⚠️ and the repair of damaged DNA.
Psychoneuroimmunology 🔄🧠🛡️
We have seen earlier that psychological and biological systems are interrelated 🔄—as one system changes, the others are often affected. The recognition of this interdependence and its connection to health and illness led researchers to form a new field of study called psychoneuroimmunology 🔄. This field focuses on the relationships between psychosocial processes 🧠 and the activities of the nervous 🧠, endocrine 🧪, and immune 🛡️ systems. These systems form a feedback loop 🔄: the nervous and endocrine systems send chemical messages in the form of neurotransmitters ⚡ and hormones 🧬 that increase or decrease immune function, and cells of the immune system produce chemicals, such as ACTH, that feed information back to the brain 🧠. The brain appears to serve as a control center to maintain a balance ⚖️ in immune function, since too little immune activity 🦠 leaves the individual open to infection and too much activity may produce autoimmune diseases ⚠️.
Emotions and Immune Function 🙂😞🛡️
People's emotions—both positive 🙂 and negative 😞—play a critical role in the balance of immune functions 🛡️. Research has shown that pessimism, depression 😞, and stress 😰 from major and minor events are related to impaired immune function 🛡️⬇️. For example, studies have compared immune variables of caregiver spouses 👩⚕️ of Alzheimer's disease patients with matched control subjects. One study found that the caregivers had lower immune function 🛡️⬇️ and reported more days of illness 🤧 over the course of about a year. Other studies have confirmed caregivers' reduced immune function and found that men's immune systems are more vulnerable than women's to care-giving stress and that care-giving does not seem to impair immune responses when new brief stressors occur.
Positive emotions 🙂 can also affect immune function, giving it a boost 🛡️⬆️. In the study by Arthur Stone and his coworkers, adult men kept daily logs 📝 of positive and negative events and gave saliva samples for analyses of antibody content. Negative events 😞 were associated with reduced antibodies only for the day the events occurred, but positive events 🙂 enhanced antibody content 🛡️⬆️ for the day of occurrence and the next two.
Some stressful situations start with a crisis 💔, and the ensuing emotional states tend to continue and suppress immune processes over an extended period of time ⏳. This was demonstrated with healthy elderly individuals 👴👵 who were taking part in a longitudinal study of the aging process. The subjects were asked to contact the researchers as soon as they were able if they experienced any major crisis, such as the diagnosis of a serious illness in or the death of a spouse or child. Fifteen subjects did so. A month after the crisis ⏱️, and again several months later, the researchers assessed the subjects' cortisol and lymphocyte blood concentrations 🩸, recent diets, weights, and psychological distress 😰.
Because the subjects were already participating in the longitudinal study, comparable data were available from a time prior to the crisis. Analysis of these data revealed that lymphocyte concentrations, caloric intake, and body weight decreased ⬇️, and cortisol concentrations and psychological distress increased ⬆️ soon after the crisis. By the time of the last assessment several months later ⏳, however, all of these measures had returned almost to the pre-crisis levels.
When people are reacting to short-term, minor events, such as doing difficult math problems ➕➖ under time pressure ⏰, changes in the number and activity of immune cells occur for fairly short periods of time—minutes or hours ⏱️, and some measures even improve. The degree of change seems to vary with the event's intensity, duration, and type—such as whether the event is interpersonal 👥 or nonsocial. Long-lasting and intense interpersonal events seem to produce especially large immune reductions ⬇️. Of course, immune system reactivity varies from one person to the next, but a person's degree of response to a type of event seems to be much the same when tested weeks apart. This suggests that an individual's reaction to specific stressors is fairly stable over time ⏳.
Psychosocial Modifiers of Immune System Reactivity 👥🧠
We saw earlier that psychosocial factors in people's lives may modify the stress they experience. Such factors seem to affect immune system responses 🛡️, too. For instance, social support 👥❤️ affects the immune function of people under long-term, intense stress ⏳😰. People who have strong social support 👨👩👧 have stronger immune systems 🛡️⬆️ and smaller immune impairments in response to stress than others with less support. Research has also demonstrated that physical exercise 🏃♂️ and psychotherapy 🧑⚕️ to reduce stress can enhance immune function 🛡️⬆️ in people infected with the AIDS virus.
A related psychosocial modifier involves describing one's feelings 🗣️✍️ about stressful events. An experiment with college student subjects 👨🎓 examined the effect of expressing such feelings on blood concentrations 🩸 of antibodies against the Epstein-Barr virus 🦠, a widespread virus that causes mononucleosis in many of those who are infected. The students were randomly assigned to three conditions that met in three weekly 20-minute sessions ⏱️ when they either described verbally 🗣️ or in-writing ✍️ a highly stressful event they had experienced or wrote about a trivial (non-stress-related) topic, such as the contents of their bedrooms 🛏️.
The subjects in each condition had the same level of immune control 🛡️ against the virus before the start of the study. But analysis of blood samples 🩸 taken a week after the last session revealed that immune control improved substantially ⬆️ in the verbal condition 🗣️, moderately in the written condition ✍️, and declined slightly in the control (trivial topic) condition. The influence of optimism 🙂 on immune function appears to depend on whether the stress is short-term ⏱️ or chronic ⏳.
Lifestyles and Immune Function 🥗🏃♂️😴
Do people's lifestyles affect the functioning of their immune systems 🛡️? Some evidence suggests that they do. People with generally healthful lifestyles 🥗🏃♂️😴—including exercising 🏃♂️, getting enough sleep 😴, eating balanced meals 🥗, and not smoking 🚭—show stronger immune functioning 🛡️⬆️ than those with less healthful lifestyles. Other studies have found that sleeping poorly 😴❌ impairs immune function 🛡️⬇️ the next day and people who smoke 🚬 are more susceptible to catching colds 🤧.
Summary 📌
In summary, stress 😰 affects health 🏥 in two ways. First 1️⃣, stress can affect health-related behaviors 🍺🚬, such as alcohol and cigarette use. Second 2️⃣, it produces changes in the body's physical systems 🧠❤️🛡️, as when the endocrine system 🧪 releases catecholamines ⚡ and corticosteroids 💊, which can cause damage to the heart ❤️ and blood vessels 🩸 and impair immune system functioning 🛡️⬇️. The physical effects of intense stress can even lead to sudden death ☠️. Psychoneuroimmunology 🔄🧠🛡️ is a new field of study that focuses on how psychosocial processes 🧠 and the nervous, endocrine 🧪, and immune 🛡️ systems are interrelated 🔄.
Stress 😰 also plays a role in many psychophysiological disorders ⚠️, such as ulcers, asthma 😮💨, tension-type and migraine headache 🤕, rheumatoid arthritis, and several skin disorders. In addition, stress is implicated in the development of hypertension ⬆️🩸, CHD 💔, and cancer 🎗️. We will study these psychophysiological disorders in detail in our later coming lectures 📘.