Skip to main content
Porträt Alexandra Schneider
Helmholtz Munich | Matthias Tunger Photodesign

Interview Heavy Rain, Heat, and Cold Stress Health

Dr. Alexandra Schneider explains the effects of extreme weather on cardiovascular diseases, such as heart attacks and strokes.

 

 

Dr. Alexandra Schneider explains the effects of extreme weather on cardiovascular diseases, such as heart attacks and strokes.

“ Living in cities means being exposed to various environmental factors. I aim to study how we can better protect health – especially for groups of people who are particularly sensitive to harmful environmental influences.”
Dr. Alexandra Schneider, Deputy Director of the Institute of Epidemiology, Helmholtz Munich

Dr. Alexandra Schneider focuses her research on cardiovascular diseases. Her main topics: the effects of weather and climate change on health and the interplay with air pollution. In addition, she investigates the health impacts of noise pollution and the benefits of green and blue spaces as part of her work on “urban health.”

Sensitivity to Weather – Is It Just a Feeling?

AS: Our relationship with the weather is shaped by two facts. First, weather is always present and cannot be turned off. Second, it is constantly changing. As a result, physiological processes aim to adapt the body to this natural environmental factor. Weather stimuli affect everyone, but only a healthy body can regulate them without discomfort. The autonomic nervous system – unconsciously controlled – manages automatic responses, regulation, and compensatory mechanisms in circulation, metabolism, and thermoregulation. If the body is weakened by age or chronic diseases, these factors can trigger discomfort and illnesses.

“Air pollution effects on health show partly similar pathomechanisms as heat or cold. Therefore, it’s very plausible that air pollution intensifies the consequences of extreme temperatures.”
Alexandra Schneider

What Role Does Air Pollution Play?

AS: Air pollution is a significant risk factor for global health. It harms most organ systems and is linked to diseases like asthma, cardiovascular diseases, COPD, pneumonia, stroke, diabetes, lung cancer, and dementia. The most recent Global Burden of Disease Study (2021) identified air pollution as the leading global risk factor, followed by high blood pressure, smoking, and poor diet. In 2020, the European Environmental Agency estimated that air pollution was responsible for 300,000 premature deaths within the EU.

“Climate change is the greatest environmental threat to human health in the 21st century.”
Alexandra Schneider

What Are the Effects of Climate Change?

AS: Climate change represents the largest environmental threat to human health in the 21st century. It brings rising global temperatures and more frequent extreme weather events, such as wildfires, heatwaves, and droughts. While the effects of cold, air pollution, and seasonal changes on cardiovascular health are relatively well-researched, the impact of heat on heart diseases is less studied. The Global Burden of Disease Study 2019 identified high temperatures as a risk factor for human health, accounting for 11.7 million lost healthy life years globally. Extreme heat and heat stress can worsen existing diseases, leading to severe health consequences.

“Heat increases the risk of heart attacks.”
Alexandra Schneider

Studies show a rise in heat-related hospitalizations for heart attacks due to climate change. Between 1987 and 2000, heart attacks were primarily caused by cold exposure, but from 2001 to 2014, heat emerged as a significant risk factor, especially for individuals with diabetes or high cholesterol levels. Extreme temperatures should therefore be recognized as a major risk factor for cardiovascular diseases, particularly for vulnerable populations.

Can Rain Be Stressful?

AS: Moderate to heavy rainfall can have protective effects through two main mechanisms. First, it can improve air quality by reducing (fine) particulate matter in the atmosphere, potentially mitigating respiratory and cardiovascular risks. It also has a cooling effect. Second, it can encourage people to spend more time indoors, thereby decreasing exposure to outdoor air pollution and extreme temperatures.

Expert Knowledge: What is PM2.5?

Fine particulate matter (PM2.5) has a diameter of 2.5 micrometers or smaller, making it invisible to the naked eye. It can penetrate deep into the respiratory system and enter the bloodstream, causing cardiovascular and respiratory diseases. Main sources of PM2.5 include traffic, industrial emissions, wood burning, agriculture, and natural sources like wildfires.

How Does Heavy Rain Affect Health?

AS: With increasing rainfall intensity, initial protective effects can be overshadowed by negative impacts. Intense rain can disrupt access to healthcare and damage infrastructure, such as power outages or loss of essential medical services. This is particularly problematic for elderly individuals and those with chronic illnesses who rely on consistent access to medication and healthcare.

“Extreme rainfall can negatively impact mental health, which in turn affects physical health." 
Alexandra Schneider


AS: Intense rainfall can compromise water and food quality by introducing pathogens, leading to diarrheal diseases, infections, and related mortality. High humidity fosters pathogen growth, which can trigger allergic reactions and respiratory problems, especially in vulnerable individuals. Rapid atmospheric pressure changes during rain can reduce oxygen levels in the body, causing cardiovascular and respiratory complications. Additionally, large temperature fluctuations associated with rainy days can impact the respiratory and cardiovascular systems.
Extreme rainfall can have profound effects on mental health, triggering stress and anxiety, worsening pre-existing mental health conditions, and indirectly contributing to an increased overall mortality rate from non-external causes.

What Can Be Done to Prevent Heart Attacks and Strokes?

Heat action plans are essential for protecting health. These plans must be developed and implemented at national, municipal, and healthcare facility levels. In summer 2023, the German Federal Minister of Health launched a national heat protection plan with ongoing further development and improvement emphasizing the involvement of general practitioners and specialists in heat-related counseling and treatment, especially for patients with preexisting conditions.

“Scientific knowledge is vital for public health: We need to build resilience to climate change—and our healthcare system is a key foundation for that. ”
Alexandra Schneider

What Role Can Healthcare Professionals Play?

AS: Cardiovascular diseases are among the leading chronic conditions contributing to heat-related hospitalizations and mortality. Cardiologists play a crucial role in recognizing the effects of heat on the cardiovascular system and the interactions between heat and medications. They can implement quick measures to minimize risks for vulnerable patients, both in clinical practice and inpatient settings.

Healthcare professionals must be well-informed about heat-associated conditions, medication interactions, and prevention strategies. Patients at risk can be monitored during the summer and contacted during heat events, offering advice on risk factors, protective measures, behavioral changes, and adjustments to cardiovascular medications. Organizational measures like scheduling appointments during cooler times of the day and limiting non-urgent procedures on hot days, as well as maintaining cool indoor environments, can further reduce health risks.

A Double-Edged Sword: Can Medications Increase Risks During Heat?

AS: Heat can alter how medications are absorbed, distributed, and eliminated, increasing the risk of side effects. For example, impaired kidney function may lead to overdosing, subcutaneous medications like insulin may act faster, and blood pressure-lowering drugs like beta-blockers may have stronger effects, further lowering blood pressure.

 

 

 

“The weather impacts health as a complex system: To understand its effects on heart attacks and strokes, we must study the interactions between barometric pressure, humidity, temperature, and air pollutants.”
Alexandra Schneider

Does the formula hold: The higher the temperatures, the greater the risk for cardiovascular diseases?

AS: Weather acts as a complex system affecting our health. To understand the impacts on heart attack and stroke, we need to examine the interactions between air pressure, humidity, temperature, and various air pollutants.

For individual factors, the impact on health is often well-documented, but this is not the case for combinations of environmental factors. During extreme heat, multiple factors change simultaneously.
Since no definitive thresholds have been established for many environmental factors, it makes sense to keep the exposure to each individual environmental factor as low as possible.

Hot or Cold – Both Are Stroke Risk Factors?


AS: Extreme temperatures, whether hot or cold, can strain the body and increase cardiovascular risks by affecting blood vessels, inflammation, and clotting.

Expert Knowledge: Why Are Heat and Cold Risk Factors? 

  • Heat: To cool down, the body dilates blood vessels (vasodilation) and sweats. This can lead to dehydration, electrolyte imbalances, and increased heart rate, raising risks for ischemia or plaque rupture in arteries. Heat also thickens the blood due to sweating and increases inflammation, damaging blood vessels further.
     
  • Cold: To conserve heat, the body constricts blood vessels (vasoconstriction), increases heart rate, and tightens muscles, leading to higher blood pressure and red blood cell concentration, stressing the cardiovascular system. Cold can also promote cholesterol crystallization in plaques and amplify inflammation, elevating heart disease risks.

How Do Environmental Factors Impact the Nervous System and Stroke Risk?


AS: Environmental stressors like heat, cold, and air pollution influence the autonomic nervous system (ANS), increasing risks for heart attacks and strokes. The ANS (Sympathetic and Parasympathetic systems) regulates the heart and brain. Overactivation of the sympathetic system can raise heart rate and blood pressure, burdening the heart and increasing heart attack risks. Strokes can disrupt the ANS, triggering arrhythmias or other heart issues. Arrythmia such as atrial fibrillation can promote blood clots which could move to the brain, thereby increasing the risk for a stroke.

How Else Does Weather Affect the Body?

AS: Environmental factors impact various body systems, including the immune system, respiratory system, cardiovascular system, and endocrine system (responsible for hormone production). Air pollution and climate change play a major role, highlighting the importance of promoting a healthy environment.

Expert Knowledge: Environmental Factors and Body Systems

  • Immune System: Nutrition, exercise, and stress affect immunity. Cold increases infection risks, while heat fosters new infections via mosquitoes or contaminated water.
  • Respiratory System: Air pollution and allergens exacerbate asthma and other lung conditions. Clean air is crucial.
  • Cardiovascular System: Air pollution, noise, and stress increase risk for heart disease, while exercise and a healthy diet offer protection.
  • Nervous System: Noise, light, and chemicals contribute to stress, sleep disorders, and neurological illnesses.
  • Endocrine System: Environmental chemicals can disrupt hormones, causing infertility, thyroid issues, and metabolic disorders.

Latest update: January 2025