How Does Stress Affect the Immune System?
A little bit of stress is good. Short-term stress, or the "fight or flight response", gives us the energy, speed, and concentration necessary to get out of sticky situations. Prolonged stress, however, is not something our body is meant to deal with. One part of the body that is particularly susceptible to the effects of chronic stress is the immune system.
The Stress Response
The hypothalamus, a tiny, pea-sized gland deep within the brain, is responsible for initiating the hormonal cascade of the stress response. Communicating through neural impulses and the release of hormones, the hypothalamus alerts the adrenal glands to jump into action. The adrenal glands lie on top of the kidneys and can release massive amounts of hormones very quickly. The two most important hormones it releases in response to stress are adrenaline and cortisol. Adrenaline causes blood pressure and heart rate to increase, speeding the delivery of oxygen to the muscles. Cortisol causes blood sugar levels to rise as well as improves the brain's ability to utilize glucose. Cortisol also has the ability to suppress immune, digestive, and reproductive function.
Most stressful situations can be resolved relatively quickly. The hypothalamus and adrenal glands respond by decreasing the amount of hormones they release, allowing heart rate, blood pressure, and the function of suppressed systems to be restored to normal. Some kinds of stress, however, can prevent this quick, down-regulation of the stress response. Trouble at work or with close family relationships can prevent stress hormone levels from returning to normal, often resulting in harmful effects on the body from chronically suppressed function.
Stress and the Immune System
The immune system is comprised of a group of specialized cells and proteins whose main function is to keep foreign organisms and objects out of the body. The immune system organizes its activities based on how much and what parts of it are needed. Cortisol, in particular, can affect this organization, causing the suppression of some parts of the immune system while allowing others to run rampant.
Stress and the Immune System: The Specifics
One of the more powerful cell types of the immune system is the T cell. While there are several variants of this cell, they are all responsible for dictating the attack against foreign organisms. Cortisol has a suppressive effect on T cells, causing immune responses to certain viruses and bacteria to proceed more slowly. This is why college students are most prone to viral infections during the week of final exams.
Another immune cell affected by stress is the neutrophil. A type of white blood cell, neutrophils are like the work horses of the immune system; they're constantly on the look-out for locations of infection where they engulf and kill foreign particles and microorganisms. Chronic stress allows the ratio of neutrophils to lymphocytes (e.g. T cells) to become unbalanced. As a result, potentially harmful inflammation is allowed to remain unchecked, causing tissue damage and pain.