In her interesting book, The Balance Within: The Science Connecting Health and Emotions, Esther Sternberg describes how the brain’s hormonal stress response balances susceptibility to inflammatory and infectious diseases. Stress stimulates hormones that repress immune cell functions that cause inflammation. Hence a rat strain that reacts more to stress is less susceptible to a common type of inflammatory disease than a rat strain that reacts less to stress. A small-scale evalution of human subjects by means of a controlled stress test found that persons with a higher stress response are less likely to suffer from a particular type of autoimmune disease. On the other hand, chronic stress is associated with greater susceptibility to infectious disease. A good balance of stress-related hormones is needed to keep the immune system active (not too much stress hormones), but not over-active (not too little stress hormones).
Humans’ behavioral response to their genetic/developed stress response creates an additional problem of balance across biology and experience. Persons consciously or unconsciously aware that they react strongly to stress (become highly distressed) have a strong biological incentive to avoid stressful situations. Thus persons with a relatively high stress-response may respond by adopting a low-stress lifestyle. Correlation between degree of stress-response and inflammatory disease in health surveys might not be negative because of this life-historical behavioral response. An important challenge for persons with a high stress-response is to find a satisfying lifestyle with a moderate amount of stress. That seems to be the kind of lifestyle that provides the best biological circumstances for avoiding both inflammatory and infectious diseases.