Research published in Psychosomatic Medicine (March 1999;61:175–180) found that stress can worsen the symptoms of a cold or the flu. The study involved 55 subjects who were injected with influenza A virus. Before exposure, participants completed questionnaires assessing their perceived stress levels. They were then quarantined and closely monitored.
Researchers measured mucus production, evaluated symptom severity, and analyzed levels of interleukin-6—a protein involved in immune and inflammatory responses. Subjects reporting the highest levels of stress experienced more severe symptoms, produced more mucus, and had significantly higher interleukin-6 levels than those reporting lower stress.
Additional evidence comes from research published in Epidemiology (May 2001;11:345–349). This study surveyed more than 1,100 staff members and students at a Spanish university, examining multiple forms of psychological stress. Individuals who perceived themselves as stressed were more likely to develop a cold than those who did not report stress. The highest incidence of colds was observed in pessimistic individuals—those with a consistently negative outlook on life.
