Optimistic people are better at handling stress and the "stress hormone" cortisol tends to be more stable in people with more positive personalities.
The study, by Concordia University's Department of Psychology, tracked 135 older adults (aged 60+) over six years, and involved collecting saliva samples five times a day to monitor cortisol levels.
This age group was selected because older adults often face a number of age-related stressors and their cortisol levels have been shown to increase.
Participants were asked to report on the level of stress they perceived in their day-to-day lives, and self-identify along a continuum as optimists or pessimists.
Each person's stress levels were then measured against their own average.
Measuring the stress levels against participants' own average provided a real-world picture of how individuals handle stress because individuals can become accustomed to the typical amount of stress in their lives.
Joelle Jobin, a PhD candidate in clinical psychology who co-authored the study with her supervisor Carsten Wrosch and Michael Scheier from Carnegie Mellon University, says "for some people, going to the grocery store on a Saturday morning can be very stressful, so that's why we asked people how often they felt stressed or overwhelmed during the day and compared people to their own averages, then analyzed their responses by looking at the stress levels over many days."
She also notes that pessimists tended to have a higher stress baseline than optimists, but also had trouble regulating their system when they go through particularly stressful situations.
"On days where they experience higher than average stress, that's when we see that the pessimists' stress response is much elevated, and they have trouble bringing their cortisol levels back down. Optimists, by contrast, were protected in these circumstances," Jobin said.
While the study generally confirmed the researchers' hypotheses about the relation between optimism and stress, one surprising finding was that optimists who generally had more stressful lives secreted higher cortisol levels than expected shortly after they awoke (cortisol peaks just after waking and declines through the day).
The study is published in the American Psychological Association's Health Psychology journal.