The big six modifiable factors for youth mental health

Six modifiable factors may hold the key to improving the mental health of Australian adolescents, write PhD candidate Scarlett Smout and Dr Lauren Gardner from the Matilda Centre at the University of Sydney.

As many doctors would know, rates of youth mental disorders have increased markedly over the past two decades. Our recently published study in the Australian and New Zealand Journal of Public Health found that 16.4% of the 6640 Year 7 students that participated across New South Wales, Queensland and Western Australia had moderate to severe anxiety symptoms and 16.7% had moderate to severe symptoms of depression.

Social determinants such as gender, socio-economic status, and educational opportunities drive inequities in mental ill-health and access to treatment. Although it’s crucial that we see policy reform to address these drivers, we must also prioritise prevention at an individual level.

The Big 6 modifiable domains

We would all love to find a silver bullet for youth mental health – with sole blame often placed on screen time – but the reality is that young peoples’ lives, strengths and risks are complex and varied. The growing evidence base in “lifestyle medicine” suggests that for adolescents, six key modifiable domains play a role in both physical and mental health.

We call these the “Big 6”: diet, physical activity, sleep, sedentary recreational screen time, alcohol use and tobacco use; and in our study, which is, to our knowledge, the largest of its kind in Australia, we found significant associations between each of the Big 6 and depression, anxiety, and psychological distress symptoms.

A proxy for privilege?

You might be thinking “but these behavioural differences could be functioning as a proxy for social and demographic differences”. Indeed, there is evidence that these behaviours are associated with social determinants.

So, in our analysis we controlled for effects of gender identity, age, cultural and linguistic diversity, relative family affluence and school affluence to look at associations between the Big 6 and mental health over and above these social determinants.

We also examined links between the social determinants themselves and mental health, finding that female-identifying and culturally and linguistically diverse adolescents had significantly higher symptoms of anxiety, depression, and psychological distress.

We found that adolescents from the highest family affluence and attending a school in the highest Index of Community Socio-educational Advantage (ICSEA) tertile had significantly lower symptoms of depression and psychological distress, but we didn’t find a difference for anxiety.

Our study found no significant differences in mental disorder symptoms between adolescents in regional versus major city areas.

Study findings: the Big 6 and mental health

First up, it’s important to note that this analysis is cross-sectional so we can’t draw conclusions about whether the Big 6 caused changes in mental health symptoms. We can, however, compare mental health symptoms between adolescents with different behaviours to find associations.

Diet

We narrowed diet to three areas: sugar-sweetened beverage (SSB) consumption, as SSBs are the leading source of added sugar in adolescents’ diets; daily fruit servings; and daily vegetable servings.

Adolescents who “never/rarely” drank SSB had the lowest mental disorder symptoms, with 24% lower anxiety symptoms, 49% lower depression symptoms, and 31% lower psychological distress symptoms compared with those who drank high amounts (≥ 14 cups per week).

Adolescents who consumed three serves of fruit daily had the lowest symptoms, with 14% lower anxiety symptoms, 37% lower depression symptoms, and 22% lower psychological distress compared with those who consumed less than one serve of fruit daily.

For vegetables, adolescents who had two serves daily had the lowest symptoms, with 14% lower anxiety, 34% lower depression, and 21% lower psychological distress compared with those who consumed less than one serve of vegetables daily.

Physical activity

The lowest mental disorder symptoms were observed in adolescents that engaged in six days of moderate to vigorous physical activity (for ≥ 60 minutes per day) in a typical week.

They had an average anxiety score 12% lower, depression score 37% lower, and psychological distress score 30% lower than adolescents who reported zero days of 60 minutes or more of moderate to vigorous physical activity.  

Sleep duration

Young people who slept an average of 10–10.5 hours per night had the lowest anxiety scores – 30% lower than those who slept for less than five hours.

Adolescents who slept 9.5–10 hours per night had the lowest depression and psychological distress scores (64% and 48% lower respectively) compared with those who slept for less than five hours.

The recommended sleep for young people aged 12–13 years is 9–11 hours, so it is encouraging that the sleep durations associated with lowest symptoms fall within that range.

Screen time

Sedentary recreational screen time varied widely across the cohort.

Young people who kept within 31–60minutes per day faired best, with 22% lower anxiety, 57% lower depression, and 48% lower psychological distress symptoms than those who engaged in eight or more hours per day.

But – perhaps more attainably – those who kept screen time within 1.5–2 hours (meeting the guidelines of ≤ 2 hours per day) still had substantially lower anxiety, depression and psychological distress symptoms.

Alcohol

Young people who had not consumed a full standard alcoholic drink in the previous six months had 20% lower anxiety symptoms, 38% lower depression symptoms, and 28% lower psychological distress symptoms than those who had drank.

Smoking

Young people who had not smoked a cigarette in the previous six months had 29% lower anxiety, 49% lower depression, and 39% lower psychological distress than those who had smoked.

Small differences matter

Adolescents getting even 30 minutes more sleep or one day more moderate to vigorous physical activity had lower psychological distress symptoms. And it was not always the case that the highest possible amounts of healthy behaviours and lowest possible levels of unhealthy behaviours aligned with the lowest mental disorder symptoms.

Modelling the Big 6 together

We analysed all the behaviours together in three models: one for anxiety, one for depression, and one for psychological distress. Sleep, screen time, and tobacco use remained significant predictors in all three models. Moderate to vigorous physical activity was also a significant predictor of psychological distress and depression but not anxiety. And fruit consumption and sugary drink consumption were significant predictors of depression only. This suggests that targeting all six behaviours might be more effective in improving mental health than focusing on them individually.

What’s next?

While this study has shown that the Big 6 may offer potential prevention targets for adolescent mental health, we need further research to establish to what extent these behaviours cause or result from symptoms.

In the interim, we know that the majority of adolescents don’t meet the Australian guidelines for diet and physical activity, screen time, and sleep. So, empowering young people to get closer to these guidelines is a step towards improving their physical – and potentially mental – health. Adolescents can find information on the Big 6, mental health, and help seeking in the Kids Helpline Self-care guide, ReachOut, and Positive Choices.

Supportive environments

Although adolescents can make changes to the Big 6 themselves, human behaviours are influenced by the environments in which we live, work and play. There are many changes that can be made at a policy- and community-level to create supportive environments for the Big 6. For diet, possible solutions include fiscal measures (eg, taxations on sugar and subsidies on fruit and vegetables); for physical activity, green space and active transport can be made more accessible (eg, improved bike lanes, pedestrian routes); for alcohol and smoking, packaging and taxation measures have shown great success, but vaping is a new challenge, with developing evidence on the best system-level approaches.

Screen time and sleep are two areas where individual- and family-level approaches may be most effective, although school bans on personal electronic devices may help, and some have suggested pushing back school start times to be better match adolescent sleep patterns; however, we believe both solutions require more evidence. 

But all this should not downplay the role that medical professionals can have in improving the Big 6 among adolescent patients. Speaking to your patients about the Big 6 behaviours and supporting them to make even small changes could help them reach a healthier and happier future.

In summary, we cannot draw conclusions about whether these six behaviours caused mental health symptoms, were the result of mental health problems, or both. Nonetheless, our study provides an important addition to the potential ways we can all help improve the mental health of young people.

Scarlett Smout is a final year PhD candidate at the University of Sydney. She wishes to acknowledge her PhD supervisors Dr Katrina Champion, Professor Nicola Newton and Dr Lauren Gardner who co-authored the ANZJPH study.

The statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of the AMA, the MJA or InSight+ unless so stated. 

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