Impact of heat on mental health emergency visits: a time series study from all public emergency centres, in Curitiba, Brazil

Introduction

Research on the impacts of climate change (CC) on mental health (MH) has substantially increased in the past few years.1 Recent work by Berrang-Ford et al, however, found that MH outcomes are least studied in the CC and health discourse globally.2 Furthermore, only a small number of studies have been carried out in low-income and middle-income countries (LMIC), such as Brazil, where the most climate-vulnerable populations live.3 A nationwide study carried out in Brazil supports that MH patients from poorer areas are more susceptible during heat.4 The authors showed that in low-income or middle-income cities, there was a 17.2% higher risk of hospitalisation after a 5°C increase in temperature, while in high-income cites, this risk was only 5.5%, for the same temperature variation.4

This difference in the heat susceptibility among patients from lower and higher income areas has been attributed, first, to the higher prevalence of common mental disorders among the poor, low educated and unemployed layers of society.5 Also, socioeconomically disadvantaged patients are at special risk of being directly exposed to heat, given inadequate housing and working conditions.5 Simultaneously, the adaptive capacity, such as access to air conditioning, is lower.6 Finally, the budget allocated to provide care for psychiatric patients in poorer countries is low—in average, limited to 1.9% of their total health funding, against 5.10% in richer nations.7 Consequently, fewer MH diagnoses are made and availability of medication for treatment is scarce, exacerbating health inequalities.

Brazil accounts for one of the highest proportions of MH disorders. In 2019, the prevalence was 16.7%, in contrast to the 13.0% global average, from the Global Burden of Diseases study.8 Regarding anxiety, the country has the second highest global prevalence: 7.4%, only behind Portugal.8 This high prevalence will place a larger number of people with MH disorders at risk of heat exposure. Moreover, the MH burden in Brazil was reported to be 2317.70 disability-adjusted life-years (DALYs) per 100 000 people—the highest in Latin America, where the average rate is 1733.40 DALYs per 100 000 people.9

The mechanisms underlying heat impact on MH are currently incompletely understood. The pathways identified in the literature include (1) impairment of the physiological body thermoregulation, caused by MH diseases and psychotropic medications6 10–12 and (2) patients inefficient cooling behaviour, given possible cognitive disability.10 Against this complex background and given that the global average temperature has already increased by 1.1°C, Berrang-Ford et al identified the need for increased research on the effects of heat exposure on MH, like this study, as most of the other MH publications analysed correlation to extreme events, for example, floods, droughts and rainfall.2 13 Therefore, we aimed to quantify the relative risk of emergency department visit (EDV) due to MH conditions (Relative risk of EDV, RR_EDV) from heat and investigate the delayed effects between exposure and outcome, by using public EDVs as proxy for MH disorder. To our knowledge, apart from China, this is the first time in LMICs that EDV is used as proxy for MH, as most studies use hospitalisation numbers. Specifically, we intended to analyse heat-vulnerability of different MH subgroups (F00–F99), suicide attempt (X60–X84), age and sex categories.

Methods

Study area and population

Curitiba is the largest capital city in southern Brazil (figure 1) with a population of 1 773 733, in 2022.14 Despite being considered an upper-middle-income city by the World Bank, the socioeconomic inequalities are evident, expressed by a Gini index of 0.525, against an average of 0.492 in the state.15 Accordingly, the households average income in the richest neighbourhood is approximately 10 times the income in the poorest neighbourhood.16

Figure 1

Brazilian territory shown in grey, with inset of the city of Curitiba (435 036 km²) and of its metropolitan region. The nine blue circles represent all the public emergency units (UPAs) in the city; the three black pins indicate the meteorological stations from where data of temperature and humidity were used; the two red pins show the meteorological sites from where air pollution data were retrieved. Variables retrieved from each monitoring site: 1. REPAR: O3 and PM10, 2. INMET Curitiba: Tmean, 3. Simepar Curitiba: Tmean and humidity, 4. Boqueirão: O3 and PM10 and 5. INMET Colombo: Tmean and humidity. The owners of the monitoring sites were: 1. Petrobras, 2 and 5: National Brazilian Meteorological Institute; 3. Paraná Environmental Monitoring and Technology System; 4. Water and Earth Institute. Source: authors. Image partly created using Mapbox.com. Met. Station, meteorological stations; T, temperature.

Results

MH in general: single-lag and cumulative risks

Table 2 displays both single-lag (a) and cumulative (b) risks for MH in general, resulting from different temperature exposures. Under extreme heat (P99), a significant increase in RR_EDV of 1.03 was observed starting at single-lag 1 (95% CI 1.00 to 1.04), which persisted until single-lag 4. The risks from individual single-lags due to extreme heat cumulated (as shown in table 2B), and peaked at lag_CUM 0–6, with 15% higher risk of EDV (RR_EDV 1.15, 95% CI 1.05 to 1.26). Effects dissipated at lag_CUM 0–8. Similar, but shorter and less intense, pattern was observed for moderate heat.

View this table:

Table 2

RR_EDV for MH in general

In contrast, both extreme and moderate cold reduced RR_EDV. Effects appeared immediately at single-lag 0 and lasted until single-lag 2, varying from RR_EDV 0.92 (95% CI 0.88 to 0.97—P1, single-lag 0) to RR_EDV 0.98 (95% CI 0.96 to 0.99—P5, single-lag 2). Cumulatively, under extreme cold (table 2B), RR_EDV reached its lowest point at lag_CUM 0–4 (RR_EDV 0.83, 95% CI 0.75 to 0.93), indicating a 17% lower risk of EDV.

Figure 2A displays all the effects observed at lag_CUM 0–6, for different temperature ranges: lower RR_EDV for cold and higher RR_EDV for heat. Two blue and two red dotted lines represent P1, P5, P95 and P99, respectively. In longer periods, lag_CUM 0–10, as presented by figure 2B, effects dissipated, and no statistically significant RR_EDV is found, in any temperature exposure.

Figure 2

Cumulative effects of temperature on RR for an EDV calculated for short-term (lagCUM 0–6 days (A) and long-term (lagCUM 0–10 (B), respectively. Reference Tmean: 18.02°C. Grey area represents the 95% CI, blue dotted lines are the extreme (P1) and moderate (P5) cold, while red dotted lines are the extreme (P99) and moderate (P95) heat. EDV, emergency department visit; RR, relative risk.

Cumulative risk, by age and sex subgroups

Table 3 displays results for complete subgroup analyses, while figure 3 presents results for MH in general (figure 3A) and also specifically for sex and age subgroups (figure 3B–F), all calculated under extreme heat (P99). Females presented higher risk of EDV, which peaked at lag_CUM 0–6 (RR_EDV 1.20, 95% CI 1.08 to 1.34), and persisted until lag_CUM 0–9 (figure 3B). Males and patients aged 0–17 showed no significant effect under extreme heat (figure 3C,D). Differently, for patients aged 18–64 the RR_EDV increased substantially (figure 3E), and at lag_CUM 0–10, RR_EDV remained still 1.16 (95% CI 1.03 to 1.32). Contrarily, elderly ≥65 had a reduced RR_EDV due to heat, and at lag_CUM 0–4, RR_EDV was 0.77 (95% CI 0.60 to 0.98) (figure 3F).

View this table:

Table 3

Subgroup analysis

Figure 3

Extreme heat effect (P99, daily Tmean 24.5°C) over different subgroups, during different lags. Tmean reference: 18.02°C. Subgroups formed for analysis were (A) MH total, (B) female, (C) male, (D) age from 0 to 17 years old, (E) age from 18 to 64 years old and (F) elderly ≥65 years old. P, percentile. Grey area represents 95% CI. EDV, emergency department visit; MH, mental health; RR, relative risk.

Cumulative risk, by MH subgroups

Two MH subgroups were under higher risk from extreme heat: patients who attempted suicide and patients with neurotic disorders (table 3). Patients attempting suicide had a higher RR_EDV of 1.21 (95% CI 1.04 to 1.41) directly at lag 0 of extreme heat. This risk gradually increased and peaked at lag_CUM 0–10, with RR_EDV 1.85 (95% CI 1.08 to 3.16)—the highest effect for this study. Given this extreme effect, we performed an extra analysis for patients attempting suicide by sex. We could observe that females had higher RR_EDV for suicide attempt than males (RR_EDV 2.53, 95% CI 1.57 to 5.16 x RR_EDV 1.51, 95% CI 0.79 to 2.93, at lag_CUM 0–10—online supplemental table S3). Additionally, patients with neurotic disorders showed an increased EDV risk initially at lag_CUM 0–2, and at lag_CUM 0–6 they presented an RR_EDV of 1.18 (95% CI 1.05 to 1.32).

In contrast, two MH subgroups showed a reduced RR_EDV from extreme heat. Patients with organic disorders presented, at lag_CUM 0–4, RR_EDV 0.60 (95% CI 0.40 to 0.89), while patients with personality disorders demonstrated, at lag 0, RR_EDV of 0.48 (95% CI 0.26 to 0.91).

This association between T_mean (x), RR_EDV (y) and lag (z) is represented by the three-dimensional (3D) graphs (figure 4). The two MH subgroups with higher risk under heat are also displayed (figure 4B,C). MH in general (figure 4A) and neurotic disorders (figure 4B) had increased RR_EDV only after a period of heat exposure. Differently, suicide attempt (figure 4C) had immediately, at lag 0, the period with the highest RR_EDV. Effects of all three reduced gradually along the lags.

Figure 4

Three-dimensional graphs of the relationship among heat (x), RREDV (y) and lag (z) for (A) MH in general, (B) neurotic disorders and (C) suicide attempt. Tmean reference: 18.02°C. MH, mental health; RREDV, relative risk of emergency department visit.

Discussion

To our knowledge, apart from China, this is the first time in LMICs that EDV was assessed as a proxy for MH disorders.1 We observed that extreme heat-related risk starts at lag_CUM 0–2, peaks at lag_CUM 0–6, with 15% increased RR_EDV and lasts until lag_CUM 0–8. Furthermore, we found a dose–response relationship, where extreme heat was associated with higher RR_EDV for MH in general than moderate heat. Our results corroborate and strengthen the literature on the high heat-susceptibility of MH in general.20 25 It is hypothesised that MH disorders and the psychotropic medications, such as antipsychotics and hypnotics, typically used as treatments, prevent a proper heat dissipation through sweating or vasodilation, thus leading to heat-related outcomes, (eg, dehydration and heatstroke).6 10–12 Further, neurotransmitter and hormonal imbalance triggered by meteorological factors can exacerbate chronic MH disorders.12 Cognitive impairment occasionally associated with MH disorders may also lead patients to non-efficient cooling behaviours, such as not keeping hydrated or taking off extra clothes.10 Although, these findings may still have been attenuated by the colder climate in Curitiba. A previous meta-analysis found that heat-related MH risk was higher in tropical and subtropical climates, whereas Curitiba city is considered temperate.26 27 So even in temperate zones, we could see higher RR_EDV of MH from extreme heat.

A previous study by da Silva et al in Curitiba measured the risk of hospitalisation for MH due to heat and air pollutants, from 2010 to 2016.28 The authors found that females and males had higher risks of being admitted to a hospital, on the day of heat exposure. However, several differences between our study and da Silva et al paper should be delineated: (1) we used EDV rather than hospitalisations for MH. In Brazil, with few exceptions, patients are first attended at the emergency centres, and only then, if accepted, transferred to a tertiary hospital after a waiting time. Therefore, using EDV rather than hospitalisation can potentially remove the bias of low hospital bed availability for MH diseases, common in Brazil and other LMICs—to better capture the short-term effect of heat.29 (2) It also expands the study population, because the emergency centres (UPAs) are completely free and accessible without referral, whereas at the hospital, doctors have a propensity of admitting only severe patients. Our sample consisted of 101 452 EDVs in a 5-year period, compared with 5397 hospital admissions in 7 years presented in da Silva et al (2020). (3) The authors did not present a RR estimate for MH in general, focusing instead on results stratified by sex and age groups. (4) Finally, our study included ICD-10th for suicide attempt and performed subgroup analysis by all MH diagnoses.

The RR_EDV from two MH subgroups increased by heat exposure: neurotic disorder (80% anxiety) and suicide attempt. A 2016 study showed that cortisol levels, an important stress hormone, increased under heat exposure.30 These hormones are also responsible for inducing anxiety symptoms, such as fear or shortness of breath, which could hypothetically explain part of this acute rise in EDV for neurotic disorders.31 Suicide attempt was the most affected condition, with 85% higher RR_EDV at lag_CUM 0–10. Heat had already been linked to aggressive and impulsive behaviours, which is the possible explanation for this increase.32 33 Another study showed that patients who had made multiple suicide attempts in the past have higher risks of new self-harm episode under heat exposure than those who were attempting it for the first time, corroborating their higher heat vulnerability.34 This suggests that heat intensity exacerbates the effect of individual characteristics, such as neurotransmitter concentrations and receptor responsivity, on suicidal and self-harm episodes.34 35 In accordance to existing literature, in our extra analysis, females presented significantly higher RR_EDV for suicide attempt than males.36

Despite previous literature indicating adverse effects of heat on patients with substance misuse, schizophrenia and mood disorders,37 we did not observe any association. Also, although there is no literature on the topic, heat was shown to have reduced RR_EDV on patients with personality disorder in this study.37 Future studies should investigate whether these groups are in fact not affected by heat exposure or if our study design could not capture them properly, which is our main hypothesis. Research is also needed to address the less prevalent conditions, such as intellectual disability and developmental disorders (autism spectrum), for which low EDV numbers may prevent accurate analyses.

We found, under extreme heat, a reduced RR_EDV of up to 23% for elderly ≥65, and 40% for patients with organic disorders, for example, dementia—MH subgroup formed mostly by elderly, as well. This is in opposition to the findings of most studies, as the elderly are likely to have disrupted heat-dissipation mechanisms.38 39 We hypothesise that, similar to the 2003 heatwave in France, both groups may have remained at home rather than seeking help.40 COVID-19 lockdowns may have also played a role. There was an abrupt decrease on EDV (online supplemental figure S4), in March 2020 and again in March 2021, when cases spread throughout the country. Given that elderly ≥65 years were the most susceptible group to COVID-19, the fear of contamination and adherence to the lockdown may have prevented them from looking for emergency centres, thus resulting in the apparent protective effect of heat.29

Patients aged 18–64 were the only age subgroup to be negatively affected by extreme heat, placing the economically active population at greatest potential burden. MH is already responsible for absenteeism from work and loss of productivity, so this evidence sheds light on the extra economic hazards potentially resulting from a rise in heat exposure associated with CC.41

Females represented 60% of our sample and were highly affected by extreme heat, while males were the minority and were not affected. Contrarily, da Silva et al found that males comprised 60% of the hospitalisation numbers in Curitiba—instead of EDV—and that the risk of hospitalisation was similarly high for both sexes. We hypothesise that females, by searching for emergency centres and receiving treatment instantaneously may avoid the need of hospitalisation afterwards, whereas this effect is not extended to males. Additionally, women receive, in general, lower income than men, which could also potentially increase their vulnerability to heat.42 Our results strengthen evidence that females are among the groups holding the highest MH prevalence and burden, and this sex difference could become more pronounced with CC.28 29

In the current study, cold exposure contributed to a reduced RR_EDV on MH in general from lag 0 until lag_CUM 0–7. Other studies have reported the same observed effect, but the literature is inconsistent.43 44 Reinforcing our results, Mullins and White indicated that the beneficial effects of cold exposure are stronger in cooler climates, as in Curitiba.45 The authors suggested that such effects are related to the reduction of sleeping disturbance under cold, but further mechanisms remain widely unknown.45 However, as CC is projected to progress in the future, the importance of exposures to cold will decrease, whereas the one to heat will increase.

Several confounders were included in the model, in order to increase robustness of our analysis. For this purpose, we collected extra data for humidity, O3 and PM10. Other potential confounders could not be used, due to data incompleteness. The sensitivity analysis can be found in online supplemental table S8. We observed that humidity and O3 influenced minimally in the result, however, we opted to keep all the variables in the main model, despite their strength, as the findings can be more trustworthy in different circumstances. Further studies are welcome in order to delineate the effects of possible confounders in the city of Curitiba.

Some limitations of this study should be considered when interpreting our results. Although EDV is a reasonable proxy indicator of health impacts of CC, the ideal outcome would have been the direct measurement of MH symptoms among the general population, using a representative survey. This is of course difficult as it requires a large sample and substantial resources in time and money. Therefore, we used EDV as the best proxy. We acknowledged that different healthcare access barriers might have biased the results. Such barriers could be due to access costs, distance to the facility or stigma. In addition, patients with MH might have stayed at home because of the extreme heat outside. Another limitation of our study is that we could only use data from the public healthcare system (SUS). According to a national report, SUS patients have, in general, lower income and educational level than patients who afford paying for private care.46 Considering that low socioeconomic status amplifies MH risks,4 our results may be of greater intensity, if compared with those who rely on the private system, as they have more adaptation means. Two lines of research are highly recommended for the future. First, studies investigating the differences between public and private patients would help delineate priorities for policy-makers in Curitiba. Second, a population-based study with MH status as outcome may increase understanding of the actual heat-related burden of MH since patients who were prevented from seeking medical care or decided not to do so for a variety of reasons, including their MH condition, would also be included.

The past 8 years—2015 to 2022—were the warmest ever reported and the next five are projected to set new heat records.47 In this context, our study calls for urgent adaptation actions targeting MH patients. Early warning systems (EWSs) have the potential to increase patient, health professional and caregiver preparedness. By strengthening awareness against the risks of heat and advising effective actions, for example, improving hydration and taking frequent showers, thousands of deaths were avoided in France, in the years following the deadly 2003 heatwave.48 Likewise, in Brazil, EWSs may prevent MH outcomes such as suicide attempts and reduce EDV numbers, reducing maintenance costs of public health. Concurrently, in primary care, the existing risk stratification could expand the focus on MH patients, followed by active search and treatment during hot periods, which would provide care in the early stages of the condition rather than waiting for severe manifestation of the outcome. This approach attempts to ensure treatment for all patients, thereby reducing healthcare access inequalities. Finally, susceptible populations would benefit from interventions to increase their adaptation capacity, such as creating local cooling centres and implementing household strategies to reduce indoor air temperature, for example, white roof painting programmes.49