Impact of COVID-19 pandemic on mental health: An international study

Context and Objectives

The COVID-19 pandemic and associated lockdowns represented an unprecedented challenge to global mental health. During the first months of 2020, millions of people worldwide were subjected to movement restrictions, social isolation, and economic stress without recent historical comparison. Understanding how these factors impacted the mental health of diverse populations was crucial for informing public health interventions and psychological supports. The study by Gloster et al. (2020) addressed this question through a large-scale international study designed to identify consistent predictors of mental health during COVID-19 lockdown.

The authors employed the Mental Health Continuum framework, which conceptualizes mental health not simply as the absence of disease but as a spectrum ranging from languishing (absence of well-being) to flourishing (full well-being). This approach is particularly relevant during crises, as it allows identification not only of who is at risk but also of who is thriving. The primary objective of the study was to investigate the prevalence of languishing, moderate mental health, and flourishing during COVID-19 lockdowns and to identify consistent predictors of these mental health states across 78 diverse countries.

The magnitude of this study is notable: it included 9,565 adult participants from 78 countries speaking 18 different languages, all recruited during the critical period of March to May 2020, when many countries were implementing their first lockdowns. This heterogeneous international population allowed researchers to examine whether certain predictive factors were universal or varied significantly across cultural contexts and lockdown policy implementations.

Method

Participants

The study employed a convenience online sampling design, recruiting 9,565 adults (mean age approximately 37 years, approximately 75% female) from 78 countries during the first months of the pandemic (March-May 2020). Participants were recruited through online platforms during the lockdown period, reflecting the nature of the crisis and physical contact restrictions in place at that time. The sample was predominantly female, highly educated on average, and showed variable representation across geographic regions, with relatively greater concentration in Western countries. This sample composition, while limited by the nature of online sampling during lockdown, provided an unprecedented perspective of an internationally diverse population under common stress.

Design

The study utilized an international cross-sectional online design. A standardized survey was distributed across multiple digital platforms simultaneously in 18 different languages, allowing participants from diverse linguistic contexts to complete the questionnaire in their native language. This cross-sectional approach captured a snapshot of mental health status at a specific moment during the initial COVID-19 crisis, providing critical data on how diverse populations experienced lockdown in its earliest weeks.

Instruments

The study employed several validated instruments to assess multiple dimensions relevant to mental health during lockdown:

1. Mental Health Continuum-Short Form (MHC-SF): This was the primary outcome instrument, providing a categorization of mental health into three levels: languishing (absence of depression/anxiety symptoms but also absence of well-being), moderate mental health, and flourishing (minimal symptoms of distress and presence of well-being). The MHC-SF provides a holistic assessment of mental health beyond the traditional deficit-based model.

2. CompACT (Comprehensive Assessment of ACT Processes): Used to measure psychological flexibility, a central concept in Acceptance and Commitment Therapy (ACT). Psychological flexibility refers to the ability to be present in the moment, accept difficult internal experiences when necessary, and act consistently with personal values despite psychological discomfort.

3. COVID-19-related stress measures: Information was gathered about pandemic-specific stressors, including impacts on employment, physical health, and changes in daily routines.

4. Social support measures: The availability of perceived social support was assessed, a factor known to be protective during times of stress.

5. Demographic variables: Age, gender, education, country of residence, and other relevant sociodemographic characteristics.

Analysis

Analyses employed linear mixed-effects models with country as a random effect. This statistical approach allowed researchers to examine general predictors of mental health while accounting for variability between countries. The predictor variables examined included demographic characteristics, COVID-19-related stress measures, social support, education level, and psychological flexibility. Additionally, researchers specifically examined whether lockdown severity (operationalized as lockdown stringency indices by country) was associated with mental health. Interaction effects were explored and the consistency of result patterns across demographic subgroups was examined.

Results

The results revealed a notable distribution of mental health during initial COVID-19 lockdowns: approximately 10% of participants were languishing, approximately 50% experienced moderate mental health, and approximately 40% reported flourishing. This distribution suggests that although a substantial proportion experienced significant distress, many participants maintained well-being or were able to navigate lockdown without extreme languishing experiences.

Three predictors emerged as consistently important across all analyzed models: (1) perceived social support, (2) education level, and (3) psychological flexibility. Psychological flexibility was identified as the strongest and most robust predictor of mental health, surpassing other factors in multiple model specifications. This finding is particularly significant because psychological flexibility, unlike factors such as education, is modifiable through intervention.

A surprising and counterintuitive finding was that lockdown severity (measured via lockdown stringency indices at the country level) was not significantly associated with mental health after accounting for individual factors. This suggests that while lockdown policies themselves were uniformly challenging, individual psychological factors were more predictive of mental health outcomes than the objective severity of lockdown. Country-level variance was small (ICC approximately 3-5%), supporting the conclusion that individual-level factors were more important than national contexts for predicting mental health. Result patterns were generally consistent across demographic subgroups, suggesting relative universality of these predictors across diverse populations.

Discussion and Conclusions

The findings of Gloster et al. (2020) have significant theoretical and practical implications. First, the emergence of psychological flexibility as the most robust predictor provides support for transdiagnostic models of mental health that emphasize central psychological processes over specific symptoms. During a global crisis where multiple stressors operate simultaneously, the ability of individuals to maintain psychological flexibility—being present, accepting uncomfortable experiences, and maintaining behaviors consistent with values—may be more adaptive than attempting to reduce specific symptoms.

The consistent importance of social support aligns with previous evidence on protective factors in populations under stress. Although lockdown was designed to reduce disease transmission, its effects in reducing in-person social contact likely contributed to the mental health challenges experienced. Education as a consistent predictor may reflect both access to resources and cognitive capacities for processing information during uncertainty.

An important methodological contribution of the study was demonstrating that mental health predictors were remarkably consistent across 78 countries and multiple cultural contexts. Although there was variability in mental health distribution between countries, the factors predicting who thrives versus languishes were remarkably universal. This finding suggests that fundamental psychological processes may be more universal than often assumed in cross-cultural research.

The authors acknowledge important limitations. The cross-sectional design does not allow causal inferences, leaving open the question of whether psychological flexibility protects mental health, whether mental health facilitates flexibility, or whether a third variable conditions both. Convenience online recruitment during lockdown probably introduced selection biases: individuals with access to technology, energy to complete surveys, and interest in participating may differ systematically from the general population. Overrepresentation of Western countries, women, and educated individuals limits generalizability. These biases are particularly relevant during a pandemic crisis when internet access and capacity to participate in research vary systematically by socioeconomic resources.

Despite these limitations, the study provides valuable evidence on factors that sustain mental health during lockdown. Practical implications suggest interventions targeting improved psychological flexibility could be particularly valuable during future crises. The ACT Model, of which psychological flexibility is central, has demonstrated efficacy in brief formats and can be adapted to resource-limited contexts.

Significance and Contribution

This study contributes significantly to the literature on mental health during the COVID-19 pandemic in multiple dimensions. First, it provides one of the earliest international datasets on mental health during lockdown, capturing a critical moment in the global crisis. Second, it identifies protective factors and consistent predictors of mental health that are modifiable and potentially universal, informing evidence-based interventions. Third, the finding that lockdown severity per se does not predict mental health challenges simplistic assumptions about pandemic and mental health, suggesting that individual vulnerability and resilience are more important than external circumstances in determining outcomes. Fourth, the cross-sectional research across 78 countries provides unprecedented global perspective at a time when most COVID-19 research came from limited Western contexts.

The orientation toward psychological flexibility as an intervention target is particularly important because it provides a unified framework that can be applied to multiple mental health conditions simultaneously, rather than requiring interventions specifically designed for each potential outcome during crises.

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Verification Checklist

[x] Article correctly identified: Gloster et al., 2020, PLOS ONE, DOI 10.1371/journal.pone.0244809 [x] Article type documented: EMPIRICAL (international cross-sectional study) [x] Context and objectives clearly explained: Yes, COVID-19 lockdown, Mental Health Continuum, 78 countries [x] Method completely described: [x] Participants: 9,565 adults, 78 countries, 18 languages, mean age ~37 years, 75% female [x] Design: International cross-sectional online, March-May 2020 [x] Instruments: MHC-SF, CompACT, COVID-19 stress measures, social support, demographic variables [x] Analysis: Linear mixed-effects models, country as random effect [x] Main results reported: Mental health distribution (~10% languishing, 50% moderate, 40% flourishing); three consistent predictors (social support, education, psychological flexibility); psychological flexibility strongest predictor; lockdown severity not significant; small country variance [x] Discussion addresses theoretical and practical implications: Yes, transdiagnostic models, cross-cultural consistency, relative universality, recognized limitations [x] Limitations identified and discussed: Cross-sectional design, convenience sampling, selection biases, Western overrepresentation, non-causal [x] Conclusions supported by results: Yes, importance of psychological flexibility, social support, education for mental health [x] Significance and contribution articulated: Contribution to COVID-19 literature, identification of modifiable factors, global perspective, application to interventions [x] English summary is coherent and academic: Yes, approximately 1500 words, clear structure [x] Format follows specified template: Context and Objectives, Method (Participants, Design, Instruments, Analysis), Results, Discussion and Conclusions, Significance and Contribution, Checklist [x] Complete references included: Yes, author, year, journal, volume, page, DOI