This systematic review synthesises evidence on the mental health impacts of climate change on vulnerable populations in Nigeria and Japan and evaluates their access to emergency healthcare services. Systematic review of peer-reviewed and grey literature. Following PRISMA 2020 guidelines, we searched MEDLINE, PsycINFO, PubMed, CINAHL, and grey literature (2015 to March 2025) for studies on climate change, mental health, and healthcare access. Inclusion criteria encompassed primary studies of vulnerable populations (e.g., displaced persons, rural women, elderly) exposed to climate-related events. Two reviewers independently screened titles/abstracts and full texts, appraised quality using CASP checklists, and extracted data. A narrative synthesis was conducted due to methodological heterogeneity. PROSPERO registration: CRD420250651981. Of 143 records identified, 8 studies (Nigeria: 5 qualitative; Japan: 3 quantitative) met inclusion criteria. In Nigeria, climate-induced displacement, flooding, and livelihood loss exacerbated anxiety, depression, and PTSD, compounded by gender disparities and inadequate healthcare infrastructure. In Japan, heatwaves increased heatstroke incidence among elderly populations, with mental health risks linked to social isolation and delayed care-seeking. Both settings highlighted systemic barriers: Nigeria’s underfunded mental health services and Japan’s stigma-related underutilization of care. CASP appraisal rated studies as moderate-to-high quality. Climate change disproportionately affects mental health in vulnerable populations, with context-specific drivers in low- versus high-income settings. Policymakers must integrate mental health into climate adaptation strategies, prioritising gender-sensitive interventions in Nigeria and age-targeted emergency responses in Japan. Strengthening healthcare access and addressing socio-cultural barriers are critical to mitigating climate-related psychological burdens.
Adebayo et al. (Fri,) studied this question.