CHICAGO, Aug. 8 (Xinhua) -- A study of young and middle-aged adults posted on the website of the University of Illinois (UI) on Wednesday found that people who are the most optimistic tend to be better sleepers.

The researchers at UI studied more than 3,500 people aged 32-51. The participants included people in Birmingham, Alabama; Oakland, California; Chicago; and Minneapolis.

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 of least optimistic to 30 of 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.

The researchers found that with each standard deviation increase, the typical distance across data points, they had 78 percent higher odds of reporting very good sleep quality in participants' optimism score.

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 percent more likely to have no symptoms of insomnia and reported less daytime sleepiness.

"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," said Rosalba Hernandez, a professor of social work at UI.

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.

While the researchers 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.

The findings have been published in the journal Behavioral Medicine.