Objective: To investigate associations between key modifiable lifestyle behaviours (sleep; physical activity; fruit, vegetable and sugar sweetened beverage consumption; screen time; alcohol use and tobacco use) and mental health among early adolescents in Australia.

Method: Cross-sectional self-report data from 6,640 Year 7 students (Mage:12.7[0.5]; 50.6% male, 48.9% female, 0.5% non-binary) from 71 schools in New South Wales, Queensland and Western Australia were analysed using multivariate linear regression adjusting for sociodemographic factors and school-level clustering.

Results: All examined behaviours were associated with anxiety, depression and psychological distress (p≤0.001), with the lowest mental health symptom scores observed in participants who slept 9.5–10.5 hours per night; consumed three serves of fruit daily; consumed two serves of vegetables daily; never or rarely drank sugar-sweetened beverages; engaged in six days of moderate-to-vigorous physical activity per week; kept daily recreational screen time to 31–60 minutes; had not consumed a full standard alcoholic drink (past six months); or smoked a cigarette (past six months).

Conclusion: Targeting modifiable risk behaviours offers promising prevention potential to improve adolescent mental health; however, further longitudinal research to determine directionality and behavioural interactions is needed.

Implications for public health: While Australian Dietary, Movement and Alcohol Guidelines target physical health, findings indicate similar behaviour thresholds may offer mental health benefits.