Introduction

Climate change has severe impacts on human and natural systems, driven by extreme weather events, droughts, floods, and rising sea levels. Unlike short-term weather changes, climate change involves long-term shifts in patterns, leading to more frequent and intense conditions, such as heatwaves. In India, heatwaves have become increasingly frequent and intense, with the number of heatwave days increasing from 413 in 1981–1990 to 600 in 2011–2020 [1]. Identifying vulnerable populations is crucial for developing strategies to mitigate health risks. Regions like Central and South America, India, and Africa are projected to face the most severe heatwaves, exacerbating risks for low-income communities, outdoor workers, and those with pre-existing conditions [2]. Recent evidence suggests that India may experience significantly more intense heatwaves, with some regions projected to face more than 30 additional days of extreme heat annually by 2050 [3]. During the 2010 Ahmedabad heatwave in India, over 1,344 excess deaths were recorded, highlighting the need for effective public health policies and targeted interventions [4]. Extreme heat vulnerability is influenced by a combination of physical and social factors, and addressing both dimensions provides a more comprehensive understanding of risk and informs strategies to reduce heat-related health impacts [5].

Understanding heat vulnerability requires considering both environmental and social factors. Recent approaches emphasize social vulnerability, which reflects the influence of socioeconomic conditions such as income, education, health status, and access to resources on a community’s capacity to respond to extreme heat [6–10]. In India, these vulnerabilities are amplified by rapid urbanization which has intensified exposure to extreme heat, driven by high population density and the urban heat island effect [11–16]. The urban heat island effect contributed to higher temperatures in densely populated areas during the 2010 Ahmedabad heatwave, exacerbating mortality risks among vulnerable groups, including the elderly, women, and the urban poor [4]. This combination of social factors and urbanization creates compounded risks: recent studies from Madhya Pradesh, for example, have shown that urban regions have experienced the highest levels of economic and social vulnerability to climate change over the past two decades [17]. The effects are particularly pronounced for socioeconomically disadvantaged groups, with evidence suggesting that low-income urban residents face up to three times higher heat exposure compared to their higher-income counterparts [3].

In India’s rapidly aging population, where adults aged 60 and above are projected to reach 319 million by 2050 [3], heatwaves disproportionately affect older adults. Studies indicate that individuals aged 75 and above are at the highest risk of adverse health outcomes from extreme heat, especially those with chronic health conditions. While India has implemented various health protection schemes, including Ayushman Bharat and state-specific insurance programs, there is a lack of comprehensive research examining how socio-demographic factors such as income, education, health insurance status, and health behaviors may influence or moderate the effects of heat exposure on health outcomes in older populations. This knowledge gap is particularly critical in India, where limited evidence exists on the roles of homeownership and access to health insurance in shaping heat-related health risks among older adults, despite significant variations in healthcare access and housing conditions across different socioeconomic groups.

This study seeks to address these gaps by examining the complex relationship between socio-demographic factors, heat exposure, and health outcomes in older adults in India. Using data from the Longitudinal Aging Study of India (LASI), this study aimed to: assess the associations between heat exposure and both physical and mental health outcomes among older adults; examine how socio-demographic factors, including income, education, and health behaviors, moderate these associations; and investigate the potential protective roles of health insurance coverage and homeownership in heat-related health outcomes. By focusing on these relationships in the context of India’s aging population and healthcare system, this study provides evidence to inform targeted interventions and policies for protecting vulnerable older adults from the health impacts of extreme heat.

Methods

Results

Of 14,690 individuals in our analytical sample (Table 1), heat-exposed individuals were more likely to be female, have never attended school, were predominantly Hindu, and have a history of smoking, but were less likely to consume alcohol or report chronic conditions such as hypertension, diabetes, or heart disease. This group also had lower health insurance coverage and economic status, with lower average income and expenditure levels. These patterns indicate that heat exposure is associated with lower socioeconomic status and higher vulnerability to certain health risks, especially when combined with higher tobacco use and disparities in health insurance coverage.

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Table 1. Descriptive statistics by exposure status.

https://doi.org/10.1371/journal.pclm.0000762.t001

Heat exposure and physical health outcomes

Regression analyses showed that heat exposure during the same month was significantly associated with poorer self-reported health (β = -0·17, p < 0·001) (Table 2, Fig 1). The negative effect of heat exposure was more pronounced among females, as indicated by a significant negative interaction between female gender and heat exposure (interaction β = -0·13, p = 0·008) (Table 3). Similarly, homeownership amplified the adverse effect of heat exposure on self-reported health; the interaction between being a homeowner and heat exposure was significant and negative (interaction β = -0·33, p < 0·001). In contrast, health insurance coverage mitigated the negative impact, as evidenced by a significant positive interaction term between health insurance and heat exposure (interaction β = 0·26, p = 0·008). These results indicate differential effects of heat exposure on self-reported health across demographic groups based on gender, housing status, and access to health insurance. Full regression results were presented in S1 Table and S2 Table.

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Table 2. Main model - Associations between heat exposure and health outcomes.

https://doi.org/10.1371/journal.pclm.0000762.t002

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Table 3. Moderating effect of socio-economic characteristics.

https://doi.org/10.1371/journal.pclm.0000762.t003

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Fig 1. Associations between heat exposure and health outcomes.

Estimated coefficients and 95% confidence intervals from regression models assessing the association between heat exposure and health outcomes among older adults in India.

https://doi.org/10.1371/journal.pclm.0000762.g001

Discussion and conclusion

This study demonstrates that heat exposure has substantial effects on both physical and mental health, as well as healthcare utilization, with significant variations influenced by demographic and socio-economic factors. Using nationally representative data, we found that individuals with heat exposure reported poorer self-rated health, increased depressive symptoms, and higher levels of fatigue and fear. Our findings reveal important disparities: individuals with lower socio-economic status, limited educational attainment, or with inadequate access to health insurance, face greater vulnerability to these adverse effects. These patterns are particularly concerning given India’s rapidly aging population and increasing frequency of extreme heat events [13,14,17].

Heat exposure is associated with significant challenges to both physical and mental health, a particular concern in India where mental health infrastructure remains limited. The decline in self-rated health among individuals exposed to heat may capture the combined effects of physiological stress and broader disruptions to daily life caused by prolonged exposure to high temperatures. In the Indian context, where many older adults live in multi-generational households and maintain active social roles, the associations with increased feelings of depression, fatigue, and fear highlight the potential psychological burden of heat exposure. While these outcomes may stem directly from the physiological impacts of heat, they might also reflect indirect stressors, such as constrained mobility, disrupted sleep, or heightened anxiety about coping with extreme conditions. The psychological impacts are particularly noteworthy given that only 41% of older Indians have access to mental healthcare services, and mental health remains heavily stigmatized.

Despite India’s efforts to expand healthcare access through initiatives like Ayushman Bharat, the association between heat exposure and outpatient healthcare utilization highlights the strain extreme heat places on healthcare systems. Increased outpatient visits may indicate acute health impacts, such as dehydration or heat exhaustion, as well as the worsening of chronic conditions. This surge in healthcare needs poses particular challenges in India, where the public healthcare system already faces significant resource constraints and where approximately 63% of healthcare expenses are paid out-of-pocket. The greater likelihood of outpatient visits among those aged 65–84 suggests disparities in vulnerability and healthcare needs. These findings underscore the importance of strengthening India’s primary healthcare infrastructure, particularly in rural areas where 70% of the elderly population resides. These findings emphasize the importance of integrating heat-related health services into existing programs like the National Programme for Health Care of the Elderly (NPHCE), implementing proactive measures such as public awareness campaigns and localized cooling interventions, to address heat-related health risks effectively.

The influence of socio-demographic factors on heat-related health outcomes highlights the complexity of vulnerability to extreme heat in India. In a country where 75% of elderly people are financially dependent on others, individuals from lower socio-economic backgrounds, including those with limited education or healthcare access, showed greater susceptibility to heat-related health impacts. These findings align with prior research emphasizing the moderating roles of socio-economic factors, such as income, education, and resource access, in shaping health vulnerabilities during heat events [1,8,20,21]. Gender differences also emerged, with women experiencing poorer health outcomes during heat exposure. This gender disparity is particularly significant in India, where older women often face multiple disadvantages: they are less likely to be financially independent (only 13% have any income), less likely to have formal education (59% are illiterate), and more likely to be widowed (42%) [8,22]. The vulnerability of older adults is further underscored in this study, with age showing mixed effects on health outcomes. The oldest group (greater than 85) demonstrated better mental health outcomes, reporting less fatigue compared to younger groups, while individuals aged 65–84 showed a higher likelihood of outpatient visits during heat exposure. These age-related differences are especially relevant as India’s elderly population is projected to reach 319 million by 2050 [9,11,14,17,23,24].

In India’s rapidly urbanizing context, disparities in access to resources like cooling centers, healthcare services, and adequate housing further compound these risks, emphasizing the importance of both basic services and housing quality in mitigating heat-related impacts [1,8,22,24]. The challenge is particularly acute given that 41% of Indian households lack proper ventilation, and only 8% have air conditioning. Social factors that increase vulnerability to heatwaves include isolation, low socio-economic status, homelessness, unsafe communities, lack of urban green space, pre-existing health conditions, outdoor occupations, and medication use. These factors amplify the risk of heat-related mortality and morbidity during heatwave events [2]. Our findings about housing align with recent evidence from urban India, where informal settlements and poorly designed housing amplify heat exposure. While homeownership was associated with reduced fatigue from heat exposure, it also correlated with worsened self-reported health under heat stress, reflecting the complex reality of housing quality in India where ownership doesn’t necessarily indicate adequate infrastructure. Studies from China and Bihar identified poor housing conditions and limited access to basic services as key risk factors for climate vulnerability [25,26]. The Government of India’s housing initiatives, such as Pradhan Mantri Awas Yojana, provide opportunities to integrate heat-resilient design, particularly crucial as 70% of buildings that will exist in India by 2030 are yet to be built. Targeted investments in infrastructure are needed to improve the adaptive capacity of vulnerable groups, such as the disabled individuals, poor women, and people living in slums [1,8,10,14,17,21,22,24,27].

Mental health vulnerability to heat exposure in India is particularly concerning given the limited mental healthcare infrastructure, with only 0·75 psychiatrists per 100,000 population. Individuals with disabilities experienced a greater increase in depressive symptoms under heat stress, indicating that pre-existing conditions amplify mental health challenges during extreme heat. While India’s disability pension scheme provides some support, the intersection of disability and heat vulnerability remains largely unaddressed in current health policies. In contrast, health insurance appeared to mitigate these effects, as insured individuals exhibited a weaker association between heat exposure and depression. This protective effect of insurance is especially relevant as India expands its health insurance coverage through schemes like Ayushman Bharat. These findings align with prior research indicating that mental illness heightens vulnerability to heat-related mortality through impaired cognitive function, behavioral challenges, medication side effects, and social isolation [8,23,24,28]. In the Indian context, where natural disasters are becoming more frequent, older adults exposed to disasters have shown significantly worse mental health outcomes, including depressive symptoms and psychiatric disorders, reinforcing the long-term psychological impacts of environmental stressors [5,23,28].

Several limitations should be noted. Self-reported health data may be subject to recall bias and misreporting. Additionally, the cross-sectional design limits the ability to establish causal or temporal links between heat exposure and health outcomes. While LASI represents India’s first comprehensive aging study, longitudinal data from future waves could provide clearer insights, as some health issues may emerge years after exposure [5,29]. A health trajectories approach may help identify opportunities for early interventions to support older adults affected by heat waves. Another limitation is the temporal resolution of the heat exposure data, which is available only at the monthly level. Despite India Meteorological Department’s extensive weather monitoring network, matching temperature data to individual exposure remains challenging. While we know that heat exposure occurred in the month of the LASI interview, it is possible that the extreme temperature days occurred after the interview. Moreover, our study could not capture informal healthcare utilization, which remains significant in India, particularly in rural areas.

Our findings have important implications for India’s public health response to climate change. Future research should explore how heat exposure affects different demographic groups, focusing on socio-economic disparities in the context of India’s diverse geographic and cultural landscape. Integration of heat action plans into existing healthcare programs, particularly the National Programme for Health Care of the Elderly, warrants evaluation. Longitudinal studies are needed to assess cumulative health impacts and the efficacy of adaptation strategies. The success of city-level heat action plans, such as in Ahmedabad, suggests the potential for scaling up these interventions nationally. Research should also evaluate community-based interventions, such as cooling centers, and the role of mental health services in reducing heat-related risks. Given India’s ambitious targets for universal health coverage, studies on climate-resilient infrastructure and early warning systems can guide policy, particularly in resource-constrained settings. Collaboration between India’s various administrative levels, central, state, and local, will be crucial in addressing social inequalities and promoting equitable resilience in urbanizing areas.

Supporting information

Acknowledgments

All co-authors have made significant contribution in study design, data analysis, result interpretation, and manuscript writing.