Climatic and meteorological exposure and mental and behavioral health: A systematic review and meta-analysis

As climate change exerts wide ranging health impacts, there is a surge of interest in the associations between climatic factors and mental and behavioral disorders (MBDs). Existing quantitative syntheses focus mainly on heat and high temperature exposure, neglecting the effects of other climatic factors and their synergies. The objective of this study is to conduct a systematic review and meta-analysis of the evidence of associations between climatic exposure and combined mental and behavioral health conditions and specific mental disorders (e.g., schizophrenia, dementia). A systematic search was conducted April 11–16, 2022 using Web of Science, Medline, ProQuest, EMBASE, PsycINFO, CINAHL, and Environment Complete. Screening and eligibility screening followed inclusion criteria based on population, exposure, comparator, and outcome guidelines. Risk of bias assessment was performed, a narrative synthesis was first presented for all studies, and random-effect meta-analyses were performed when at least three studies were available for a specific exposure-outcome pair. Certainty of evidence was evaluated following the Grading of Recommendations Assessment, Development and Evaluation (GRADE) tool. The search process yielded 7696 initial results, from which we identified 88 studies to include in the review set. Climatic factors reported included air temperature, solar radiation/sunshine, barometric pressure, precipitation, relative humidity, wind direction/speed, and thermal index. Outcomes including MBD incidences (e.g., schizophrenia, mood disorders, neurotic disorders), mental health-related mortality, and self-reported psychological states. Meta-analysis showed that heatwaves (pooled RR = 1.05, 95 % CI = 1.02–1.08) and extreme high temperatures (99th percentile: pooled RR = 1.18, 95 % CI = 1.08–1.29) were associated with higher risk of MBD. Cold extremes, however, were not associated with MBD risk. The findings further identified an association between increases in a thermal index (i.e., apparent temperature) and elevated risk of MBD (pooled RR = 1.06, 95 % CI = 1.03–1.12); specifically, a 99th percentile high temperature was associated with increased schizophrenia risk (pooled RR = 1.07, 95 % CI = 1.01–1.12). Risk of bias assessment showed most studies to have low or moderately low risks, while a few studies were rated probably high in confounding, selection bias, outcome measurement, and reporting bias. GRADE evaluation revealed moderate certainty of evidence on thermal comfort index and MBD, but low certainty related to air temperature or sunshine duration. These findings call attention to the heterogeneity of exposure measures and the utility of thermal indices that consider the synergistic effects of meteorological factors. Methodological concerns such as the linearity assumption and cumulative effects are discussed.