It is well known that chronic stress and illness are related. For example, psychological stress in humans raises the risk of heart disease, colds and flu. And chronic stress in animals is also well known to lead to diseases such as upper respiratory or lower urinary tract infections.
But how does such stress lead to illness? New research published recently in the Proceedings of the National Academy of Sciences (1) found that the adrenal hormone cortisol plays a critical role in the illness caused by stress.
Released in greater amounts in times of stress, cortisol helps suppress the body’s immune response to infections, suppressing inflammation responses like coughing, sneezing, or fever. But when levels of cortisol remain high, the body may become less sensitive to it — a condition called cortisol or glucocorticoid "resistance."
So in other words, when we are stressed out, we overproduce cortisol, making our immune system incapable of turning "off" the inflammation response. If we're exposed to a virus while we are also dealing with chronic stress, the study found that we'd also be much more likely to get sick and suffer from more intense symptoms (1).
In other words, many of the symptoms of a cold, for example, are not caused directly by the virus, but rather, they're caused by the inflammatory response to the infection. We want the body to produce enough of inflammation to fight off the infection, but not so much that we experience worsened symptoms.
The Bottom Line:
Chronic stress may raise the risk of sickness by creating a state of resistance to the hormone cortisol, which, in turn, interferes with appropriate regulation of inflammation. Because inflammation plays an important role in the onset and progression of a wide range of diseases, this model may have broad implications for understanding the role of stress in health.
Although we do no know if the same phenomenon of stress-induced cortisol resistance exists in animals, it is certainly possible. We certainly do know that physical and psychological stress can induce disease in domestic animals (2-4).
- Cohen S, Janicki-Deverts D, Doyle WJ, et al. Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk. Proceedings of the National Academy of Sciences (PNAS) 2012; ,doi:10.1073/pnas.1118355109.
- Westropp JL, Kass PH, Buffington CA. Evaluation of the effects of stress in cats with idiopathic cystitis. American Journal of Veterinary Research 2006;67:731-6.
- McCobb EC, Patronek GJ, Marder A, et al. Assessment of stress levels among cats in four animal shelters. Journal of the American Veterinary Medical Association 2005;226:548-555.
- Stephens DB. Stress and its measurement in domestic animals: a review of behavioral and physiological studies under field and laboratory situations. Advanced in Veterinary Science and Comparative Medicine 1980;24:179-210.