How does stress weaken the immune system?

Kent Holtorf, MD
Endocrinology Diabetes & Metabolism
Current research suggests that a low immunity due to stress can set up the body for a vicious cascade of events. If the body can no longer keep a virus or bacteria in check, whether it is Epstein Barr virus, Cytomegalovirus, human herpesvirus 6 (HHV6), mycoplasma or Lyme, a cycle of dysfunction can occur that involves the centers in the brain that control hormone production, pain and the sleep cycle, as well as suppression of energy production (mitochondria dysfunction) and the immune system. This results in a multi-system illness that requires a multi-system treatment.
A study from Ohio State University suggests that exposure to acute stress triggers an increase in the number and activity of T cells -- a type of white blood cell that seeks and destroys infectious germs and viruses. This response makes evolutionary sense: The sight of a predator provokes fear, which in turn prepares the immune system to resist infection from a possible injury. So, is what’s good for the caveman good for the corporate exec? Yes and no. Limited bouts of stress can do your body good, not only helping you resist infection in the short term but also enhancing immune activity for weeks and even months, according to research. Stress in short doses can also help promote longevity by preventing damaged proteins from accumulating in the body. Chronic stress, on the other hand, can aggravate arthritis, increase abdominal fat, accelerate aging on a cellular level and ultimately undermine your immune system.
Anthony L. Komaroff, MD
Internal Medicine
Based on studies in people, some researchers report that stressful situations can reduce various aspects of human 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 researchers speculate that long-term stress releases an ongoing 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 a major hurricane 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.
Dr. Kathleen Hall
Preventive Medicine
Sheldon Cohen, Ph.D., professor of psychology at the Carnegie Mellon University, gave 400 people a questionnaire designed to quantify the amount of stress they were under. He then exposed them to nose drops containing cold viruses. Ninety percent of the stressed subjects caught a cold. They had elevated levels of corticotrophin releasing factor, which interferes with the immune system.
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Many people would be surprised that the immune system, the gastrointestinal tract and stress interact, but that is what the most recent of a number of studies shows. In a study on mice, researchers demonstrated that psychological stress causes almost immediate changes to the gut bacterial population, and that some of these affected sub-populations strongly influence the effect that stress has on immunity.

In the study, the researchers exposed mice to social disruption, which is known to cause increases in circulating cytokines (hormones of the immune system), which themselves induce enhanced reactivity in the immune system. The researchers found that social disruption altered bacterial counts of some gut bacteria sub-populations, particularly when the bacteria were assessed immediately after stress exposure. Stress exposure increased the relative abundance of bacteria in the genus Clostridium, which often causes prolonged and severe diarrhea.

Not only does stress affect the gut bacterial population, but these organisms are also required for activation of the immune system. Furthermore, we can now see that stress, via its effect on gut bacteria, and hence the immune system (IL-6) can change brain function. We know this because IL-6 activates a certain enzyme (IDO), which actually "steals" or siphons off, tryptophan from its normal metabolic pathway (i.e. conversion into serotonin and then melatonin) and instead converts it into chemicals that increase activity of glutamate (in depression) at an excitatory -- and sometimes toxic -- receptor (NMDA) in the brain. The result of all of this is increased depression, anxiety, and reduced memory. In mice this effect can take months to reverse.

The upshot is that stress, the gut, the brain and the immune system are really intimately linked, and inseparable.
Alice Domar
When we are first confronted with stress, our immune system is enhanced. But the effect is short-lived, according to Robert Sapolsky’s book Why Zebras Don’t Get Ulcers. After an hour, stress begins to have the opposite effect and suppresses immunity. If you develop serious, long-term stress, the immune system can plummet between 40 and 70 percent below normal.
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Susan S. Blum, MD
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Stress directly suppresses your immune cells so they don’t respond well to an invading virus or bacteria. Cortisol also directly lowers an immunoglobulin in your digestive tract that keeps the good bacteria happy and other bacteria and yeast at bay. This imbalance in your gut can hurt your killer T-Cell army which needs healthy gut bacteria to mature properly.

Dr. David L. Katz, MD, MPH
Preventive Medicine

Hormones and the immune system are directly linked. Hormonal imbalance leads to imbalances in white blood cell production, and the behavior and communication that allow white blood cells to function.

Dr. Michael Roizen, MD
Internal Medicine
We know that hazardous chemicals, too much sun, and radioactivity can age your immune system and increase your risk of cancer. Stress clearly weakens our immune response -- the death of a loved one, for example, measurably decreases the number of T cells (a kind of white blood cell that is important for immune defenses) in the bloodstream for as long as a year after the event. Even small but chronic nagging stresses such as the toilet fixture that won't stop running weakens the immune response. These nagging stresses and major life event stresses clearly age the immune system.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.