CHAMPAIGN, Ill. -- People who are the most optimistic tend to be better sleepers, a study of young and middle-aged adults found.

More than 3,500 people ages 32-51 were included in the study sample. The participants included people in Birmingham, Alabama; Oakland, California; Chicago; and Minneapolis.

The research was led by Rosalba Hernandez, a professor of social work at the University of Illinois.

"Results from this study revealed significant associations between optimism and various characteristics of self-reported sleep after adjusting for a wide array of variables, including socio-demographic characteristics, health conditions, and depressive symptoms," Hernandez said.

Participants' levels of optimism were measured using a 10-item survey, which asked them to rate on a five-point scale how much they agreed with positive statements such as "I'm always optimistic about my future" and with negatively worded sentences such as "I hardly expect things to go my way."

Scores on the survey ranged from six (least optimistic) to 30 (most optimistic).

Participants reported on their sleep twice, five years apart, rating their overall sleep quality and duration during the prior month. The survey also assessed their symptoms of insomnia, difficulty falling asleep and the number of hours of actual sleep they obtained each night.

A subset of the participants was part of an ancillary sleep study based in Chicago and wore activity monitors for three consecutive days - including two weeknights and one weekend night. Participants wore the monitors on two occasions a year apart.

The monitors collected data on their sleep duration, percent of time asleep and restlessness while sleeping.

Hernandez and her co-authors found that with each standard deviation increase - the typical distance across data points - in participants' optimism score they had 78% higher odds of reporting very good sleep quality.

Likewise, individuals with greater levels of optimism were more likely to report that they got adequate sleep, slumbering six to nine hours nightly. And they were 74% more likely to have no symptoms of insomnia and reported less daytime sleepiness.

According to a 2016 report by the Centers for Disease Control and Prevention, about 1 in 3 U.S. adults fails to get adequate sleep, escalating their risks of many chronic diseases.

"The lack of healthy sleep is a public health concern, as poor sleep quality is associated with multiple health problems, including higher risks of obesity, hypertension and all-cause mortality," Hernandez said. "Dispositional optimism - the belief that positive things will occur in the future - has emerged as a psychological asset of particular salience for disease-free survival and superior health."

Although a significant and positive association was found between optimism and better-quality sleep, Hernandez suggested that the findings should be interpreted cautiously.

While the scientists aren't sure of the exact mechanism through which optimism influences sleep patterns, they hypothesize that positivity may buffer the effects of stress by promoting adaptive coping, which enables optimists to rest peacefully.

"Optimists are more likely to engage in active problem-focused coping and to interpret stressful events in more positive ways, reducing worry and ruminative thoughts when they're falling asleep and throughout their sleep cycle," Hernandez said.

The findings, published recently in the journal Behavioral Medicine, bolster those of a prior study, in which Hernandez and her co-authors found that optimists ages 45-84 were twice as likely to have ideal heart health.

Kiarri N. Kershaw, Juned Siddique, Honghan Ning, and Donald M. Lloyd-Jones, all of Northwestern University; Julia K. Boehm of Chapman University; Laura D. Kubzansky of Harvard University; and Ana Diez-Roux of Drexel University co-wrote that study. That paper was published in the journal Health Behavior and Policy Review in 2015.

The sample for the current study was drawn from the Coronary Artery Risk Development in Young Adults study, which explored the development and progression of cardiovascular disease risk factors in a U.S. sample of non-Hispanic white and African American adults.