Impact Of Rising Heatwave Conditions On Heart Attacks And Stroke-Related Emergencies In India

During pre monsoon summers, India is home to 98 of the world's 100 hottest cities, and three of its five warmest years have occurred in the past decade. While heatwaves could become up to 30 times more frequent by the end of the century, official records show 10,000-20,000 deaths between 2000 and 2020, a figure widely believed to be significantly underreported. Beyond immediate effects like heat stroke and dehydration, a far more systemic risk is already unfolding: the impact of rising temperatures on cardiovascular health. Heatwaves, in particular, are emerging as a major public health threat due to their increasing intensity and duration. For India, already facing a high burden of hypertension, diabetes, and cardiovascular disease, this raises urgent questions about preparedness.

Heat And Cardiovascular Risk: Understanding The Link

The human body relies on a finely balanced system to regulate temperature. During extreme heat, this balance is disrupted. Blood vessels dilate to release heat, the heart works harder to maintain circulation, and fluid loss through sweating increases the risk of dehydration. Dehydration leads increasing clotting risk, resulting in heart attacks and strokes

These physiological changes can be dangerous, especially for individuals with existing diseases. Dehydration increases blood viscosity, raising the risk of clot formation. Electrolyte imbalances (such as serum Sodium and Potassium) can disrupt heart rhythms (leading to irregular heartbeats), while fluctuations in blood pressure place additional strain on the heart. Together, these responses increase the likelihood of heart attacks and strokes.

Emerging evidence highlights how even small increases in temperature can have large-scale effects. Studies show that each 1 degrees Celsius rise in temperature is associated with a 2% increase in cardiovascular mortality, demonstrating the population-level impact of rising heat.

Who Faces The Greatest Risk?

The health impacts of heat are not evenly distributed. Older adults, particularly those over 65, face higher risks due to reduced thermoregulatory capacity and a greater likelihood of underlying conditions. Individuals with hypertension, diabetes, high cholesterol, or coronary artery disease are also more vulnerable, as heat can destabilize otherwise controlled conditions.

Socio-economically disadvantaged populations face compounded risks. Limited access to cooling, safe housing, clean water, and healthcare increases both exposure and vulnerability. Outdoor workers, daily wage earners, and residents of densely populated urban areas often experience prolonged heat exposure with little protection.

Migrant and informal workers, including construction labourers and street vendors, are especially exposed, often working long hours under direct sunlight. Beyond heatstroke, prolonged exposure is linked to worsening cardiovascular and respiratory conditions, mental health stress, and reduced productivity-deepening both health and economic vulnerabilities.

What Emerging Evidence From India Suggests

Recent multi-city research across India has found a consistent association between rising temperatures and increased cardiovascular mortality. Heatwaves, in particular, are associated with significantly higher daily mortality than during non-heatwave periods. A study published in Environment International found that heatwaves with a daily mean temperature exceeding the 97th percentile for 2 consecutive days were associated with a 14.7% increase in daily mortality. Cities such as Delhi, Ahmedabad, and Hyderabad are experiencing longer and more intense summers. Nearly 65 million people living in urban slums face extreme indoor heat due to overcrowding, poor ventilation, and limited access to water and electricity. Several regions have already crossed 40 degrees Celsius, with some areas nearing 45 degrees Celsius, underscoring the growing frequency and severity of extreme heat events.

Beyond Heat: The Broader Climate-Health Interface

The relationship between climate change and cardiovascular health extends beyond heat alone. Air pollution, which often worsens with rising temperatures, is a major risk factor for heart disease. And it interacts with heat in increasing adverse outcomes. Further extreme weather events can disrupt access to healthcare, medication, clean water, and nutrition, making chronic conditions harder to manage.

Despite this growing body of evidence, awareness of climate-related cardiovascular risks remains limited among both patients and healthcare providers, highlighting a critical gap in preparedness.

Reframing Heatwaves As A Public Health Priority

As India experiences record-breaking temperatures across several states the World Hypertension Day serves as a timely reminder that hypertension management can no longer be viewed in isolation from environmental and climate-related risks. It highlights the importance of blood pressure control; the link between heat exposure and cardiovascular risk becomes even more relevant. Hypertension remains underdiagnosed and poorly managed in many parts of India, leaving millions vulnerable.

Addressing this challenge requires both individual and systemic action. Staying hydrated, avoiding peak heat hours, and monitoring blood pressure can help reduce risk at the individual level. In rural areas, staying hydrated, avoiding outdoor work during peak afternoon heat, and resting under tree shade or in well-ventilated spaces can help reduce the risk of heat-related illnesses. Traditional cooling drinks such as chaas, nimbu pani, and aam panna, along with regular water intake, can also help the body cope better in extreme heat. However, these must be supported by broader interventions-strengthening heat action plans, improving access to healthcare, ensuring availability of cooling spaces, and increasing public awareness.

Looking Ahead

Heatwaves are no longer seasonal anomalies; they are an evolving public health challenge. Their impact on cardiovascular health, though less visible, is significant and growing.

Addressing this will require an integrated approach that brings together climate science, public health, and urban planning, along with more localized data and targeted interventions.

The question is no longer whether rising temperatures affect heart health but whether we are prepared to respond in time.

[By Prof. (Dr) Dorairaj Prabhakaran, Executive Director and Dr Poornima Prabhakaran, Deputy Director & Head - Environmental Health and Senior Research Scientist, Centre for Chronic Disease Control (CCDC)]

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