Everyone should aim to eat, move, and snooze for the betterment of their body and mind. That’s why good habits around sleep, diet, and exercise are dubbed the “big three” healthy lifestyle factors. Together, they reduce the risk of conditions like depression and anxiety. And conversely, deficiencies in any or all of these behaviors can negatively impact mood and outlook.

But of these three factors, can you guess which is the strongest predictor of mental well-being? You don’t have to—we already know the answer from research published in Frontiers in Psychology. It’s sleep.

More specifically? It’s sleep quality, followed closely by sleep quantity. This suggests that, while you should, of course, prioritize all three for optimal health and longevity, taking extra care to work on your sleep habits could be the most beneficial strategy for keeping your spirits high and minimizing stress, worry, and mood dips.

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The Methodology

Researchers from the department of psychology at the University of Otago, in Dunedin, New Zealand, surveyed more than 1,100 young men and women from New Zealand and the U.S. Participants were given an online survey measuring their sleep, exercise, and nutritional habits.

The study also included “outcome measures of depressive symptoms, measured by the Center for Epidemiological Depression Scale (CES-D), and well-being (measured by the Flourishing Scale).” And the researchers controlled for covariates (like demographics, ethnicity, and body mass index, among other factors).

The Findings

The results revealed that sleep quality, or how well they sleep, followed closely by sleep quantity, or how much they sleep, were the largest indicators of depression levels and overall well-being, or “flourishing.” (Inadequate, shallow, and/or interrupted sleep, for instance, has been associated with increased risk of mood disorders and emotion regulation in children and adolescents.) According to the published paper, “Individuals who slept inside the range of 8 to 12 hours per night (not more or less) and who had better sleep quality reported fewer depressive symptoms.”

Falling just behind sleep is physical activity, the second highest predictor of depressive symptoms. Exercise releases endorphins that help raise your spirits and boost energy, and regular physical activity has been shown to help treat depression and anxiety. On the other hand, lack of activity is associated with poorer mental health in adults. Diet, though crucial, appeared to be the weakest indicator of depressive symptoms and low well-being out of the three. “Only one dietary factor—raw fruit and vegetable consumption—predicted greater well-being, but not depressive symptoms when controlling for covariates,” the authors noted.

The Caveat

In these studies, it’s important to note whether the results are causal or correlational. (Causal means that one behavior directly leads to an outcome, while correlational merely points to a relationship between the behavior and outcome.) Since the measurements in this study were self-reported via survey and only observed, not changed or tested in any way, all results are purely correlational. But the patterns revealed in the analysis offer an intriguing insight into the potential hierarchy of modifiable lifestyle behaviors. Going forward, these findings may help guide future research and treatment for mood disorders to focus on maximizing sleep quality to improve mental health, particularly in adolescents.

As for how this affects you? Take this as yet another reminder not to skimp on valuable sleep, keep up that steady fitness routine, and eat as many fresh, unprocessed foods as you can.


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