Does an optimistic attitude boost one’s immune system? University of Kentucky psychologist Suzanne Segerstrom has been studying this subject for years, and her latest research, just published in the journal Psychological Science, provides evidence of a link between upbeat expectations and immunological strength.
In a study of 124 first-year law students, Segerstrom and her co-author, Sandra Sephton, examined the relationship between personal optimism and cell-mediated immunity (CMI), which plays a central role in protecting against viral infections. At five points over the course of the school year — in August, October, December, January and February — participants answered a series of questions and had their CMI measured through a simple skin test.
To gauge their optimism level, they were asked to what degree they agreed with a series of statements, including “I will be less successful than most of my classmates” and “It’s unlikely that I will fail.” A separate survey measured the level of positive and negative emotions they were feeling at that point in time.
The end-of-year results were decisive. “Changes in CMI across time correlated with changes in optimism,” the researchers report. “When optimism increased, so did CMI. When optimism decreased, so did CMI.”
Looking deeper into the data, Segerstrom found an increased level of positive emotions predicted increases in cell-mediated immunity. However, shifts in an individual’s level of negative emotions such as depression and anxiety did not predict changes in CMI.
This suggests a simple lack of tension or worry isn’t sufficient to prompt an immune system response. Rather, this positive physiological change appears to require actual happiness to kick in.
“This dynamic relationship between expectancies and immunity has positive implications for psychological interventions to improve health — particularly those that increase positive affect,” the researchers conclude. Indeed, it suggests the practitioners of positive psychology, who study ways people can cultivate healthy emotions such as contentment and hope, are onto something important.
Segerstrom cautions that this study did not focus on underlying or “dispositional” levels of optimism. Her previous research suggests a naturally upbeat disposition “often correlates with better cellular immunity under normal circumstances.” But it has also been linked to lowered immunity during times of extreme stress.
In contrast, this study measured “situational expectancies” — the belief that you’re likely to succeed at a specific goal. According to Segerstrom, that sort of focused optimism is linked to a rise in short-term positive emotions, and those, “in turn, are associated with more robust immunity.”
In other words, the Little Engine That Could was a disease-free diesel.