Sleep quality is the strongest predictor of depressive symptoms and well-being in young people, more so than other commonly cited health factors such as a good diet, physical activity and sleep quantity, new research determined. 

In a paper published in Frontiers in Psychology on Dec. 10, a team of researchers from New Zealand studied a total of 1,111 young adults between 18-25 years old, investigating whether sleep, physical activity or diet were more important in predicting depressive symptoms and well-being. The participants, who were based in New Zealand and the U.S., answered an online survey that measured their typical sleep quantity and quality, their physical activity and their consumption of different types of food. 

Shay-Ruby Wickham, a Ph.D. student at the University of Otago in New Zealand and lead author of the paper, told The Academic Times that other research has studied each behavior alone, but that the behaviors are not often grouped together. “Previous research has examined each of these behaviors in isolation of each other, but we wanted to examine whether one of these behaviors may be more important than the others in predicting depressive symptoms and well-being in young adults,” Wickham said. 

Sleep, physical activity and diet have long been associated with health in young adults, but which of these three behaviors most strongly predicts mental health and well-being is not well studied or understood, according to the researchers. 

“Sleep is a fundamental part of good mental health and well-being, yet is often one of the first things we compromise when life gets busy,” Wickham said. “Our research identified three modifiable health behaviors that correlated with better mental health and well-being in young adults: getting good quality sleep, exercising and eating more raw fruits and vegetables, in that order.”

Wickham and the other researchers found that sleep quality was the strongest predictor of depressive symptoms and well-being, followed by sleep quantity and physical activity. Raw fruit and vegetable consumption was the only dietary factor that predicted greater well-being, but not depressive symptoms.

The research also took into account the participants’ demographics, socioeconomic status, body mass index, alcohol use, smoking, health conditions and measures of depressive symptoms and well-being. Depressive symptoms were measured by the Center for Epidemiological Depression Scale, a 20-item self-ranking questionnaire, and well-being was measured by the Flourishing Scale, an eight-item self-ranking questionnaire.

Sleep quantity has been associated with increased depression and negative affect, or the experience of distressing emotions, in clinical populations, but sleep quality generally does not receive the same attention in academic research as quantity, the authors noted.

In the study, Wickham and the other researchers found that on average, participants slept approximately seven hours per night, rated their sleep quality at the “a little or somewhat refreshed” level, and engaged in physical activity approximately three days per week. 

The ideal sleep quantity was between 8-12 hours per night. Depressive symptoms were lowest for young adults who slept 9.7 hours per night, and “flourishing” was highest for young adults who slept eight hours per night.

If an individual slept for less than eight hours or more than 12, he or she was associated with higher depressive symptoms and lower “flourishing.” The researchers did not find any significant differences based on where the participant lived. 

Dietary factors were not found to predict depressive symptoms, which the authors noted was an unexpected finding. And unhealthy food consumption in general did not significantly predict mental health or well-being. Participants reported eating an average of approximately three servings of fruit and vegetables per day, which is less than the recommended five servings per day.

“Knowing the importance of each of these lifestyle behaviors, singularly or in combination with each other, and the hierarchical order of importance will inform mental health interventions at both the population and individual level,” the authors said in the study.

“Health promotion interventions targeting sleep, diet and exercise within young adult populations may help to promote optimal mental health and well-being within this at-risk population, as targeting one individual behavior may not always improve other health behaviors,” they continued.

The authors suggested that future research in this area should use objective measures such as accelerometer data to track hours of sleep and physical activity. Further studies could also dig deeper into exercise, and examine whether intensity and duration of physical activity have different effects than frequency of physical activity alone.

“Future lifestyle interventions targeting sleep quality may be most beneficial at improving mental health and well-being. However, physical activity and diet should not be disregarded, particularly as they also uniquely predicted differences in depressive symptoms ... and well-being,” the authors said.

The study, “The Big Three Health Behaviors and Mental Health and Well-Being Among Young Adults: A Cross-Sectional Investigation of Sleep, Exercise, and Diet,”was published in Frontiers in Psychology on Dec. 10. Shay-Ruby Wickham of the University of Otago was the lead author. Natasha A. Amarasekara, Adam Bartonicek and Tamlin S. Conner, all of the University of Otago, served as co-authors.