October 16, 2011

the stress connection

Modern medicine, which once treated the connection between emotions and physical health with skepticism, has come to appreciate the closely linked relationship of mind and body. A wide variety of maladies, including stomach upset, hives, and even heart disease, are linked to the effects of emotional stress. But although the relationship between stress and immune function is being studied by a number of different types of scientists, so far it is not a major area of research for immunologists.

Studying the relationship between stress and the immune system presents difficult challenges. For one thing, stress is difficult to define. What may appear to be a stressful situation for one person is not for another. When people are exposed to situations they regard as stressful, it is difficult for them to measure how much stress they feel, and difficult for the scientist to know if a person’s subjective impression of the amount of stress is accurate. The scientist can only measure things that may reflect stress, such as the number of times the heart beats each minute, but such measures also may reflect other factors.

Most scientists studying the relationship of stress and immune function, however, do not study a sudden, short-lived stressor; rather, they try to study more constant and frequent stressors known as chronic stress, such as that caused by relationships with family, friends, and co-workers, or sustained challenges to perform well at one’s work. Some scientists are investigating whether ongoing stress takes a toll on the immune system.

But it is hard to perform what scientists call “controlled experiments” in human beings. In a controlled experiment, the scientist can change one and only one factor, such as the amount of a particular chemical, and then measure the effect of that change on some other measurable phenomenon, such as the amount of antibodies produced by a particular type of immune system cell when it is exposed to the chemical. In a living animal, and especially in a human being, that kind of control is just not possible, since there are so many other things happening to the animal or person at the time that measurements are being taken.

Despite these inevitable difficulties in measuring the relationship of stress to immunity, scientists who repeat the same experiment many times with many different animals or human beings, and who get the same result most of the time, hope that they can draw reasonable conclusions.

Some researchers place animals into stressful situations, such as being trapped in a small space or being placed near an aggressive animal. Different functions of their immune systems, and their health, are then measured under such stressful conditions. On the basis of such experiments, some published studies have made the following claims:

* Experimentally created “stressful” situations delayed the production of antibodies in mice infected with influenza virus and suppressed the activity of T cells in animals inoculated with herpes simplex virus.
* Social stress can be even more damaging than physical stress. For example, some mice were put into a cage with a highly aggressive mouse two hours a day for six days and repeatedly threatened, but not injured, by the aggressive mouse — a “social stress.” Other mice were kept in tiny cages without food and water for long periods — a “physical stress.” Both groups of mice were exposed to a bacterial toxin, and the socially stressed animals were twice as likely to die.
* Isolation can also suppress immune function. Infant monkeys separated from their mothers, especially if they are caged alone rather than in groups, generate fewer lymphocytes in response to antigens and fewer antibodies in response to viruses.

Many researchers report that stressful situations can reduce various aspects of the cellular immune response. A research team from Ohio State University that has long worked in this field suggests that psychological stress affects the immune system by disrupting communication between the nervous system, the endocrine (hormonal) system, and the immune system. These three systems “talk” to one another using natural chemical messages, and must work in close coordination to be effective. The Ohio State research team speculates that long-term stress releases a long-term trickle of stress hormones — mainly glucocorticoids. These hormones affect the thymus, where lymphocytes are produced, and inhibit the production of cytokines and interleukins, which stimulate and coordinate white blood cell activity. This team and others have reported the following results:

* Elderly people caring for relatives with Alzheimer’s disease have higher than average levels of cortisol, a hormone secreted by the adrenal glands and, perhaps because of the higher levels of cortisol, make fewer antibodies in response to influenza vaccine.
* Some measures of T cell activity have been found to be lower in depressed patients compared with nondepressed patients, and in men who are separated or divorced compared with men who are married.
* In a year-long study of people caring for husbands or wives with Alzheimer’s disease, changes in T cell function were greatest in those who had the fewest friends and least outside help.
* Four months after the passage of Hurricane Andrew in Florida, people in the most heavily damaged neighborhoods showed reduced activity in several immune system measurements. Similar results were found in a study of hospital employees after an earthquake in Los Angeles.

In all of these studies, however, there was no proof that the immune system changes measured had any clear adverse effects on health in these individuals.

Taken from: http://www.health.harvard.edu/flu-resource-center/how-to-boost-your-immune-system.htm

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