Emerging and prevailing determinants of population mental health

Abstract

To mitigate the mental health burden during and after the COVID-19 pandemic, both emerging and prevailing determinants of population mental health need to be addressed. This thesis aimed to identify major determinants by assessing how emerging and prevailing determinants may influence population mental health.

Mental health consequences of COVID-19 pandemic have been well-documented. However, the quality of studies has varied substantially. I therefore conducted a systematic review and meta-analysis to critically appraise and synthesise the evidence on mental disorders, risk factors, and vulnerable groups following COVID-19 and past epidemics (n=255 studies from 50 countries). The meta-analysis showed that one in five randomly selected adults had a current mental disorder during COVID-19. This review also established that longitudinal studies with pre-pandemic data are very much needed but lacking.

Accordingly, I conducted the first longitudinal study to examine the evolution and risk factors of population mental health under a COVID-19 elimination strategy without lockdowns (11 follow-ups from 2020–2021, n≥1000). The appropriate pandemic response has been questioned in global populations. Concerns over the elimination strategy include the potential trade-off with the economy and public health, particularly the mental health impact of more stringent interventions. However, changes in mental disorders under the elimination strategy have been rarely assessed. Population mental health remained largely stable in Hong Kong during the elimination strategy when sustained periods of zero local cases were attained. Using population attributable fractions, I estimated that risk of COVID-19 infection, life disruptions, financial loss, loneliness, and political changes each contributed to common mental disorders during COVID-19. Thus, this study provided empirical support that saving lives, protecting the economy, and safeguarding population mental health may not need to be in conflict during a pandemic. The elimination strategy could therefore be an appropriate initial pandemic response.

For prevailing determinants of population mental health, I focused on childhood neglect due to the rising number of left-behind children worldwide. The long-term association of childhood neglect with mental disorders is unclear due to strong confounding from childhood environment. Using a sibling study (n=1106, from 505 sibling groups), I showed that childhood neglect was associated with current common mental disorders in adults, independently of shared childhood environment. This could suggest potential long-term mental consequences in millions of left-behind children and other children who experienced neglect during COVID-19.

Lastly, I also assessed the protective role of family harmony, as resilience factors are crucial to mitigating the mental health toll of COVID-19 pandemic but are scarcely reported. I first showed that survey mode and question wording had little effect on the associations of family harmony with related attributes in a randomised factorial trial (n=956), and further examined family harmony as an effect modifier for childhood neglect.

In conclusion, I provided causally robust estimates on COVID-19 pandemic and childhood neglect as major determinants of population mental health. As such, syndemic interactions between emerging and prevailing determinants could result in an even greater mental health burden. Ongoing monitoring and multilevel interventions targeting these determinants are therefore needed to protect population mental health.