In prehistoric times, the physical changes in response to stress were an essential adaptation for meeting natural threats. Even in the modern world, the stress response can be an asset for raising levels of performance during critical events such as a sports activity, an important meeting, or in situations of actual danger or crisis.

If stress becomes persistent and low-level, however, all parts of the body's stress apparatus (the brain, heart, lungs, vessels, and muscles) become chronically over- or under-activated. Such chronic stress may produce physical or psychological damage over time. Acute stress can also be harmful in certain situations, particularly in individuals with preexisting heart conditions.

Psychological Effects of Stress

Studies suggest that the inability to adapt to stress is associated with the onset of depression or anxiety. In one study, two-thirds of subjects who experienced a stressful situation had nearly six times the risk of developing depression within that month.

Some evidence suggests that repeated release of stress hormone produces hyperactivity in the HPA system, and disrupts normal levels of serotonin, the nerve chemical that is critical for feelings of well-being. Certainly, on a more obvious level, stress reduces the quality of life by reducing feelings of pleasure and accomplishment. In addition, relationships are often threatened in times of stress.

Nevertheless, some stress may be beneficial. For example, some research has suggested that stress may be a risk factor for suicide. However, a 2003 study found a higher risk for suicide only in women reporting both low and very high stress. Those with moderate stress levels had the lowest risk.

Heart Disease

The effects of mental stress on heart disease are controversial. Stress can certainly influence the activity of the heart when it activates the automatic part of the nervous system that affects many organs, including the heart. Such actions and others could theoretically affect the heart badly in several ways:

Sudden stress increases the pumping action and rate of the heart, while at the same time causing the arteries to constrict (narrow). This restricts blood flow to the heart. A 2002 study suggested that such actions may be responsible for some cases of acute stress that have been associated with a higher risk for serious heart problems. These problems include heart rhythm abnormalities and heart attacks, and even death in people with heart disease.
Emotional effects of stress alter the heart rhythms, which could pose a risk for serious arrhythmias (rhythm abnormalities) in people with existing heart rhythm disturbances.
Stress causes blood to become stickier (possibly in preparation of potential injury), increasing the likelihood of an artery-clogging blood clot.
Stress appears to impair the clearance of fat molecules in the body, raising blood-cholesterol levels, at least temporarily.
Chronic stress may lead to the production of immune factors called cytokines. Cytokines produce a damaging inflammatory response, which is now believed to be responsible for damage to the arteries. Such damage contributes to heart disease.
Studies have reported an association between stress and hypertension (high blood pressure), which may be more pronounced in men than in women. According to some evidence, people who regularly experience sudden spikes in blood pressure (caused by mental stress) may, over time, develop injuries in the inner lining of their blood vessels. In one 20-year study, for example, men who periodically measured highest on the stress scale were twice as likely to have high blood pressure as those with normal stress.

Evidence is still needed to confirm any clear cut relationship between stress and heart disease. For example, a 2002 study in Scotland found no greater risk for actual heart disease or heart events even in men who reported higher mental stress. In fact, higher stress was associated with fewer heart events. Men with high stress levels did tend to complain of chest pain and to go to the hospital for it more often than those with lower stress. They also went to the hospital more often.

Evidence has linked stress to heart disease in men, particularly in work situations where they lack control. The association between stress and heart problems in women is weaker, and there is some evidence that the ways women cope with stress may be more heart-protective. In one study, men were more apt than women to use alcohol or eat less healthily in response to stress than women, which might account for their higher heart risks from stress. Different stressors may affect genders differently. In one study, work stress was associated with a higher risk for heart disease in men, but marital stress -- not work stress -- was associated with more severe heart disease in women with existing heart problems.

Stress Reduction and Heart Disease. Studies in 2001 and 2002 suggest that treatments that reduce psychological distress improve long-term outlook in people with heart disease, including after a heart attack. Some evidence indicates that stress management programs may reduce the risk of heart attacks by up to 75% in people with heart disease. Specific stress management techniques may help some problems but not others. For example, acupuncture in one study helped people with heart failure but had no effect on blood pressure. Relaxation methods, on the other hand, may help hypertensive individuals.

Stroke

One survey revealed that men who had a more intense response to stressful situations, such as waiting in line or problems at work, were more likely to have strokes than those who did not report such distress. In some people, prolonged or frequent mental stress causes an exaggerated increase in blood pressure. In fact, a 2001 study has linked for the first time a higher risk for stroke in adult white men and elevated blood pressure during times of stress.

Effect on the Immune System

Chronic stress affects the immune system in complicated ways, and may produce various effects.

Susceptibility to Infections. Chronic stress appears to blunt the immune system's response to infections, and may even impair a person's response to immunizations. Several studies have shown that people under chronic stress have low white blood cell counts and are vulnerable to colds. And once any person catches a cold or flu, stress can make symptoms worse. People who carry the herpes virus or HIV may be more susceptible to viral activation following exposure to stress. Even more serious, some research has found that HIV-infected men with high stress levels progress more rapidly to AIDS when compared to those with lower stress levels.

Inflammatory Response. Some evidence suggests that chronic stress triggers an over-production of certain immune factors called cytokines, which in excess levels can have very damaging effects. In fact, such findings may partly explain the association between chronic stress and numerous diseases, including heart disease and asthma.

Cancer

Current evidence does not support the idea that stress causes cancer or recurrence in cancer survivors. For example, a 2002 study reported no association between stressful life events and recurrence in women who had been treated for breast cancer. Nevertheless, some animal studies suggest that lack of control over stress (not simply stress itself) had negative effects on immune function and contributed to tumor growth. Although stress reduction techniques have no effect on survival rates, studies show that they are very helpful in improving a cancer patient's quality of life.

Gastrointestinal Problems

The brain and intestines are strongly related, and are controlled by many of the same hormones and parts of the nervous system. Indeed, some research suggests that the gut itself has features of a primitive brain. It is not surprising then that prolonged stress can disrupt the digestive system, irritating the large intestine and causing diarrhea, constipation, cramping, and bloating. Excessive production of digestive acids in the stomach may cause a painful burning.

Irritable Bowel Syndrome. Irritable bowel syndrome (or spastic colon) is strongly related to stress. With this condition, the large intestine becomes irritated, and its muscular contractions are spastic rather than smooth and wave-like. The abdomen is bloated, and the patient experiences cramping and alternating periods of constipation and diarrhea. Sleep disturbances due to stress can make irritable bowel syndrome even worse.

Peptic Ulcers. It is now well-established that most peptic ulcers are either caused by the H. pylori bacteria or the use of nonsteroidal anti-inflammatory (NSAID) medications (such as aspirin and ibuprofen). Nevertheless, studies still suggest that stress may predispose someone to ulcers, or sustain existing ulcers. Some experts estimate that social and psychological factors play some contributing role in 30 - 60% of peptic ulcer cases, whether they are caused by H. pylori or NSAIDs. In any case, some experts believe that the anecdotal relationship between stress and ulcers is so strong that attention to psychological factors is still warranted.

Inflammatory Bowel Disease. Although stress is not a cause of inflammatory bowel disease (Crohn's disease or ulcerative colitis), there are reports of an association between stress and symptom flare-ups. One study, for example, found that while short term (past month) stress did not significantly exacerbate ulcerative colitis symptoms, long term perceived stress tripled the rate of flare-ups compared to patients who did not report feelings of stress.

Eating Problems

Stress can have varying effects on eating problems and weight.

Weight Gain. Often stress is related to weight gain and obesity. Many people develop cravings for salt, fat, and sugar to counteract tension and, therefore, gain weight. Weight gain can occur even with a healthy diet, however, in some people exposed to stress. In addition, the weight gained is often abdominal fat, a predictor of diabetes and heart problems.

The release of cortisol, a major stress hormone, appears to promote abdominal fat and may be the primary connection between stress and weight gain. Cortisol is a glucocorticoid, and glucocorticoids, along with insulin, appear to be responsible for stress-related food cravings. A 2005 study showed that such hormonally induced cravings for "comfort foods" may have a biological benefit for managing stress. Ingestion of comfort foods appears to reduce the negative hormonal and behavioral changes associated with stress, which might lessen the impact of stress on an individual. However, the long-term health risks of carrying excess abdominal fat are significant.

Weight Loss. Some people suffer a loss of appetite and lose weight during periods of stress. In rare cases, stress may trigger hyperactivity of the thyroid gland, stimulating appetite but causing the body to burn up calories at a faster than normal rate.

Eating Disorders. Chronically elevated levels of stress chemicals have been observed in patients with anorexia and bulimia. Some studies, however, have not found any strong link between stress and eating disorders. More work is needed to determine if changes in stress hormones are a cause or result of eating disorders.

Diabetes

Chronic stress has been associated with the development of insulin-resistance, a condition in which the body is unable to use insulin effectively to regulate glucose (blood sugar). Insulin-resistance is a primary factor in diabetes. Stress can also exacerbate existing diabetes by impairing the patient's ability to manage the disease effectively.

Pain

Researchers are attempting to find the relationship between pain and emotion, but the area is complicated by many factors, including effects of personality types, fear of pain, and stress itself.

Muscular and Joint Pain. Chronic pain caused by arthritis and other conditions may be intensified by stress (according to a study on patients with rheumatoid arthritis, however, stress management techniques do not appear to have much effect on arthritic pain). Psychological distress also plays a significant role in the severity of back pain. Some studies have clearly associated job dissatisfaction and depression to back problems, although it is still unclear if stress is a direct cause of the back pain.

Headaches. Tension-type headache episodes are highly associated with stress and stressful events. Sometimes the headache doesn't even start until long after a stressful event is over. Some research suggests that tension-type headache sufferers may actually have some biological predisposition for translating stress into muscle contractions. Among the wide range of possible migraine triggers is emotional stress (although the headaches often erupt after the stress has eased). One study suggested that women with migraines tend to have personalities that over-respond to stressful situations.

Sleep Disturbances

The tensions of unresolved stress frequently cause insomnia, generally keeping the stressed person awake or causing awakening in the middle of the night or early morning. In fact, evidence suggests that stress hormones can increase during sleep in anticipation of a specific waking time.

Sexual and Reproductive Dysfunction

Sexual Function. Stress can lead to diminished sexual desire and an inability to achieve orgasm in women. Stress response can also cause temporary impotence in men. Part of the stress response involves the release of brain chemicals that constrict the smooth muscles of the penis and its arteries. This constriction reduces the blood flow into and increases the blood flow out of the penis, which can prevent erection.

Premenstrual Syndrome. Some studies indicate that the stress response in women with premenstrual syndrome may be more intense than in those without the syndrome.

Fertility. Stress may even affect fertility. Stress hormones have an impact on the hypothalamus gland, which produces reproductive hormones. Severely elevated cortisol levels can even shut down menstruation. One interesting small study reported a significantly higher incidence of pregnancy loss in women who experienced both high stress and prolonged menstrual cycles. Another reported that women with stressful jobs had shorter periods than women with low-stress jobs.

Effects on Pregnancy. Old wives' tales about a pregnant woman's emotions affecting her baby may have some credence. Stress may cause physiologic alterations, such as increased adrenal hormone levels or resistance in the arteries, which may interfere with normal blood flow to the placenta. Maternal stress during pregnancy has been linked to a higher risk for miscarriage, lower birth weights, and increased incidence of premature births. Some evidence also suggests that stress experienced by expectant mothers can even influence the way in which the baby's brain and nervous system will react to stressful events. Indeed, one study found a higher rate of crying and low attention in infants of mothers who had been stressed during pregnancy.

Memory, Concentration, and Learning

Stress affects the brain, particularly memory, but the effects differ significantly depending on whether the stress is acute or chronic.

Effect of Acute Stress on Memory and Concentration. Studies indicate that the immediate effect of acute stress impairs short-term memory, particularly verbal memory. On the plus side, high levels of stress hormone during acute stress have been associated with enhanced memory storage and greater concentration on immediate events.

Effect of Chronic Stress on Memory. If stress becomes chronic, sufferers often experience loss of concentration at work and at home, and they may become inefficient and accident-prone. In children, the physiologic responses to chronic stress can clearly inhibit learning. Chronic stress in older people may play an even more important role in memory loss than the aging process. In one study, for example, older adults with low stress hormone levels tested as well as younger adults in cognitive tests: those with higher stress levels tested 20 - 50% lower.

Studies have connected long-term exposure to excess amounts of cortisol (a major stress hormone) to shrinking of the hippocampus, the brain’s memory center. For example, two studies reported that groups who suffered from post-traumatic stress disorder (Vietnam veterans and women who suffered from sexual abuse) displayed up to 8% shrinking of the hippocampus. It is not yet known if this shrinking is reversible.

Other Disorders

Allergies. Stress has been related to skin allergies. In fact, some research suggests that stress, not indoor pollutants, may actually be a cause of the so-called sick-building syndrome. Sick-building syndrome produces allergy-like symptoms, such as eczema, headaches, asthma, and sinus problems, in office workers.

Skin Disorders. Stress plays a role in worsening numerous skin conditions, including hives, psoriasis, acne, rosacea, and eczema. Unexplained itching may also be caused by stress.

Unexplained Hair Loss (Alopecia Areata). Alopecia areata is hair loss that occurs in localized (individual) patches. The cause is unknown, but stress is suspected as a player in this condition. For example, hair loss often occurs during periods of intense stress, such as mourning.

Teeth and Gums. Stress has now been implicated in increasing the risk for periodontal disease, which is disease in the gums that can cause tooth loss.

Substance Abuse

People under chronic stress often turn to alcohol abuse or tobacco use for relief. The damage these self-destructive habits cause under ordinary circumstances is compounded by the physiological effects of stress itself. Many people also resort to abnormal eating patterns or passive activities, such as watching television. The results of a national survey, released in February 2006, show that: "Americans engage in unhealthy behaviors such as comfort eating, poor diet choices, smoking and inactivity to help deal with stress."

Alcohol affects receptors in the brain that reduce stress. Lack of nicotine increases stress in smokers, which creates a cycle of dependency on smoking. One study indicated that nicotine has calming effects in women but not in men. In fact, in the study, smoking increased aggression in men.

The cycle is self-perpetuating: a sedentary routine, an unhealthy diet, alcohol abuse, and smoking all promote heart disease. They also interfere with sleep patterns, and lead to increased rather than reduced tension levels. Drinking four or five cups of coffee, for example, can cause changes in blood pressure and stress hormone levels similar to those produced by chronic stress. Animal fats, simple sugars, and salt are known contributors to health problems.

Review Date: 10/25/2006
Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital