Study participants who had a positive emotional style weren't infected as often and experienced fewer symptoms compared to people with a negative emotional style, say Sheldon Cohen, Ph.D., of Carnegie Mellon University and colleagues, writing in the July issue of Psychosomatic Medicine.
Cohen's team interviewed 334 healthy volunteers three evenings a week for two weeks to assess their emotional states. The volunteers described how they felt that day in three positive-emotion areas: vigor, well-being and calm. They were also questioned about three categories of negative feelings: depression, anxiety and hostility.
Other scientists have speculated that people who typically report experiencing negative emotions are at greater risk for disease and those who report positive emotions have less risk, says Cohen.
After their assessment, each volunteer got a squirt in the nose of a rhinovirus -- the germ that causes colds. The researchers kept the subjects under observation for five days to see whether or not they became infected and how they manifested symptoms.
"We found that experiencing positive emotions was associated with greater resistance to developing a common cold," Cohen reports. "Increases in positive emotional styles were linked with decreases in the rate of clinical colds, but a negative emotional style had no effect on whether or not people got sick."
A positive emotional style actually had no effect on how often volunteers were infected (as measured by replication of the virus) but produced fewer signs and symptoms of the illness, says Cohen. This suggests that inflammatory chemicals produced by the body may link the positive emotional style with colds.
Further analysis revealed that good health practices and lower levels of certain hormones did not account for the link between positive emotional style and illness.
Since the average person catches two to five colds a year, developing psychological risk profiles and considering ways to enhance positive emotion might reduce the risk of colds -- and by extension, other infectious diseases.
The study was supported by grants from the National Institute of Mental Health and the John D. and Catherine T. MacArthur Foundation Network on Socioeconomic Status and Health.
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