Sleep Quality, Not Just Hours, May Predict Young Adults' Mental Health Best

Between 2018 and 2019, more than 1,100 young adults in the United States and New Zealand sat down to an online survey about how they were feeling and how they lived. They were between 18 and 25. They were asked about their mood and wellbeing, what they ate, how much they exercised, and how they slept. They were also asked how refreshed they usually felt when they woke up, a question that is an established marker of good sleep quality.

The answers were analysed by researchers at the University of Otago in New Zealand, led by Shay-Ruby Wickham of Otago Medical School. Their aim was to put sleep, diet and exercise into a single analysis and see which one best predicted mental health. Earlier studies had mostly looked at one factor at a time, even though in real life the three are tangled together. The team noted that research examining all three behaviours together is limited.

Sleep quality came out on top. It was the strongest predictor of good mental health, ahead of physical activity, which ranked second, and ahead of diet. Wickham called this surprising, because sleep recommendations tend to focus on quantity rather than quality. The familiar advice is to get eight hours.

Hours still showed a pattern. People who slept close to 10 hours a night reported fewer depressive symptoms, while those who slept under 8 hours or more than 12 reported more. On diet, eating moderate servings of raw fruit and vegetables each day was associated with better wellbeing.

The participants were a varied group. Some ate vegetarian or vegan diets, some were taking antidepressants for existing conditions, and fewer than a third identified as male. The researchers adjusted their analysis to account for those differences.

The study's limits are plain. Nobody's sleep, exercise or diet was changed, so the results show links between behaviours and outcomes, not causes. Everything rests on self-reported answers rather than direct observation or health assessments. Some parts of the questionnaire used a single question, a choice meant to encourage more people to respond, so the authors say more comprehensive measures are needed.

The researchers suggest, cautiously, that young adults prioritise good sleep, and that future lifestyle interventions targeting sleep quality may do the most for mental health and wellbeing. They also say diet and exercise should not be disregarded, describing them as secondary but still significant factors. Young adulthood is a period of big shifts in routine, work, living situations and sleep patterns, which is part of why the question matters.

The Otago team has begun analysing data from a separate study of young New Zealand adults, who were assessed daily for two weeks on wellbeing, lifestyle, diet, sleep and exercise. That work has not yet been peer reviewed. The current research was published in Frontiers in Psychology. Practical suggestions for better sleep quality include a wind-down routine after dark, putting screens away and dimming lights before bed.