Researchers in the field of psychoneuroimmunology (PNI) study the ways in which the immune system and the nervous system communicate with each other and impact people's mental and emotional health. Even though the field is relatively new, many studies have been designed to examine the influence of immune and nervous systems on the psychological consequences of stress. PNI research suggests that chronic stress can lead to or exacerbate mood disorders such as depression and anxiety, bipolar disorder, cognitive (thinking) problems, personality changes, and problem behaviors.
Stress and Depression
Byproducts of stress hormones can act as sedatives (chemical substances which cause us to become calm or fatigued). When such hormone byproducts occur in large amounts (which will happen under conditions of chronic stress), they may contribute to a sustained feeling of low energy or depression. Habitual patterns of thought which influence appraisal and increase the likelihood that a person will experience stress as negative (such as low self-efficacy, or a conviction that you are incapable of managing stress) can also increase the likelihood that a person will become depressed.
It is normal to experience a range of moods, both high and low, in everyday life. While some "down in the dumps" feelings are a part of life, sometimes, people fall into depressing feelings that persist and start interfering with their ability to complete daily activities, hold a job, and enjoy successful interpersonal relationships. The term Major Depression is used to describe such periods of extended, unremitting and profound depression. Symptoms of Major Depression may include: sleep problems; fatigue; appetite changes; feelings of worthlessness, self-hate, and guilt; an inability to concentrate or make decisions; agitation, restlessness, and irritability; withdrawal from typical pleasurable activities; and feelings of hopelessness and helplessness. Depression is also associated with an increase in suicidal thinking and suicidal actions, and may make a person more vulnerable to developing other mental disorders. For more information about Major Depression, please see our Major Depression topic center. Additional information about Suicide can be found in our Suicide Topic Center.
Stress and Bipolar Disorder
Chronic and/or severe stress can also negatively affect people with Bipolar Disorder. This illness, also known as manic depression or bipolar affective disorder, involves dramatic shifts in mood, energy level, and behavior from the highs of mania (one pole) to the lows of major depression (the opposite pole).
Mania is characterized by a euphoric (joyful, energetic) mood, hyper-activity, a positive, expansive outlook on life, an inflated sense of self-esteem, and a sense that most anything is possible. When in a manic state, individuals with bipolar disorder tend to experience a decreased need for sleep, racing thoughts, rapid speech (wherein the words won't come out fast enough to keep up with their racing thoughts) and heightened distractibility. Manic individuals typically show poor judgment and impulsivity, and are prone to engaging in risky or dangerous behaviors and activities.
Individuals with Bipolar Disorder shift from ("cycle" is the term used by mental health professionals) Mania to the symptoms of Major Depression, which we described above. Bipolar individuals who are in a depressed state often lose interest in things that used to give them pleasure; develop sleep problems; constantly feel tired and fatigued; and have distressed, negative, and unhappy moods, irritability, a short temper, and/or agitation. In addition, anger, guilt, failure and hopeless feelings may be experienced.
People with Bipolar Disorder cycle between manic and depressed mood states over the course of days, weeks, or months. This mood cycling disrupts everyday functioning; affecting energy, activity levels, judgment, and behavior. Stress can trigger either a depressive or manic mood state in someone with a genetic vulnerability to Bipolar Disorder. Stress can also worsen a Bipolar mood episode once it has begun, increasing it's intensity and/or extending it's duration across time. For more information about Bipolar Disorder, please see our related topic center.
Stress and Anxiety Disorders
Some people who are stressed may show relatively mild outward signs of anxiety, such as fidgeting, biting their fingernails, tapping their feet, etc. In other people, chronic activation of stress hormones can contribute to severe feelings of anxiety (e.g., racing heartbeat, nausea, sweaty palms, etc.), feelings of helplessness and a sense of impending doom. Thought patterns that lead to stress (and depression, as described above) can also leave people vulnerable to intense anxiety feelings.
Anxiety or dread feelings that persist for an extended period of time; which cause people to worry excessively about upcoming situations (or potential situations); which lead to avoidance; and cause people to have difficulty coping with everyday situations may be symptoms of one or more Anxiety Disorders. Anxiety Disorders (such as Generalized Anxiety Disorder, Post traumatic Stress Disorder or Panic Disorder) are one of the most commonly diagnosed mental disorders today. You can read more about the Anxiety Disorders by visiting our Anxiety Disorders Topic Center. Specialized Information on Post Traumatic Stress Disorder appears here.
Stress and Cognitive Functioning
The continuous presence of stress hormones in the body may alter the operation and structure of some aspects of the nervous system. More specifically, stress hormones may decrease the functioning of neurons (brain cells) in a region of the brain known as the hippocampus (a part of the brain that is important for laying down new long-term memories) and in the frontal lobes (the part of the brain that is necessary for paying attention, filtering out irrelevant information, and using judgment to solve problems). As a result, people who are chronically stressed may experience confusion, difficulty concentrating, trouble learning new information, and/or problems with decision-making.
Stress and Personality Changes
The term personality is used to describe the consistent individual patterns of thoughts, emotion, and behavior that characterize each person across time and situations. Each individual's personality is thought to be influenced by both an inherited "genetic" component (usually called temperament) and by their interactions with the environment. Some people experience personality changes in response to stress hormones, which are part of their internal environment. The following changes in personality are not uncommon to observe in people who are stressed:
- Aggressive feelings and behavior
- Decreased interest in appearance
- Decreased concern with punctuality
- Obsessive/compulsive behavior (trying to cope with unwanted repeated thoughts or obsessions, by engaging in compulsive behavior rituals such as counting, checking, washing, etc.)
- Reduced work efficiency or productivity
- Lying or making excuses to cover up poor work
- Excessive defensiveness or suspiciousness
- Problems in communication
- Social withdrawal and isolation
- Impulsivity (expressed as impulse buying, gambling, sexual behavior, or similar)