Stress and the immune system

"In the last twenty years or so, research has begun to support the theory that letting go of suppressed emotions can be beneficial to the physical body. This is especially true of stress, because so many studies have focussed on how that particular emotional state affects the body. One of the landmark stress studies was published in the New England Journal of Medicine in 1991*. In this study, 420 men and women first took surveys on a variety of factors, including their stress levels. Then, some of the subjects were given a nasal spray that contained saline, while the rest were given a nasal spray that contained the common cold virus (don't worry, they were all told ahead of time that this would be happening, although they did not know which spray they would get). Can you guess what happened?The ones who reported being more stressed initially developed a full-on cold, while the ones who reported being less stressed initially were better able to fight it off. Of all the factors listed in the surveys, stress was the only one that made a significant difference in the outcome. In other words, this study showed that holding on to stress makes you more vulnerable to developing disease.

Since this groundbreaking study, hundreds of other studies have shown that stress is associated not only with the common cold but also with more serious things like heart disease, autoimmune disorders, and cancer. It is still difficult for researchers to prove whether stress by itself can cause cancer, mostly because it would be unethical to make one group purposefully relaxed and then see which developed cancer. However, what researchers know for certain is that stress weakens the immune system, and the immune system plays a key role in detecting and removing cancer cells from the body."
Kelly A. Turner, in Radical Remission – Surviving Cancer Against All Odds

*Psychological stress and susceptibility to the common cold.