Extreme climate events increase heart disease risk, new study reveals

A novel study has revealed a link between extreme weather and the risk of cardiovascular disease among middle-aged and older adults in 157 Chinese cities. Based on a city’s climate and location, exposure to extreme heat, cold, and precipitation each increases the risk of heart disease.

The findings of the study in the American Journal of Preventive Medicine, provide evidence for policymakers across different regions to develop targeted strategies protecting vulnerable populations during extreme climate events.

Extreme climate events (ECEs) have intensified globally as climate change accelerates, posing unprecedented threats to public health. China’s rapidly aging population, with 400 million people over 60 years of age projected by 2035, reflects a growing population with increased vulnerability.

Cardiovascular diseases (CVDs), the leading causes of death in China, are particularly prevalent among older adults. Prior studies have linked CVDs to extreme temperatures.

Lead investigator Ya Fang, MD, Ph.D., says, “By integrating macro (city-level) and micro (individual-level) evidence with advanced spatial and causal analysis methods, we have painted a more complete picture of how climate extremes threaten heart health.

“Our study focuses on CVD in middle-aged and older adults—a high-risk age group—and identifies actionable subgroups, thereby providing a basis for adaptive urban-rural planning and clinical interventions, filling critical gaps in climate-health policy.”

The researchers from the School of Public Health, Xiamen University, China, employed spatial econometric methods to examine the impact of extreme climate events on city-level CVD prevalence among middle-aged and older adults in China using longitudinal data (2015–2020) from the China Health and Retirement Longitudinal Study (CHARLS) and the Chinese Longitudinal Aging Social Survey (CLASS).

They validated the link between individual ECE exposure and CVD risk using a double machine learning approach.

Key results include:

• Extreme heat (above 38ºC) increased city-level CVD prevalence with a weakening east-west impact gradient; each additional heat ECE day was associated with 1,128 more CVD cases per 100,000 people.
• Extreme cold (below -10ºC) increased city-level CVD prevalence with a weakening west-east impact gradient; each additional cold ECE day was associated with 391 more CVD cases per 100,000 people.
• Causal inference analysis revealed that each heat ECE day increased individual CVD risk by 3.044%, cold ECE days by 0.110%, and precipitation ECE days by 1.620%.

Heterogeneity analysis identified high-risk subgroups:

• Heat ECEs affected pre-retirees, smokers, and residents in high ozone (O₃) areas (with higher BMI mitigating risk).
• Cold ECEs impacted pre-retirees, individuals with high BMI, and high-O₃ populations.
• Precipitation ECEs most strongly affected older adults, rural residents, pre-retirees, and unmarried individuals.

The investigators explain that BMI-related risk depends on temperature intensity. Above 38°C, the physics of heat exchange reverses: heat flows from the environment into the body rather than escaping. In this scenario, body fat acts as a protective physical barrier, blocking external heat and reducing cardiovascular strain.

In contrast, below -10°C, the mild insulation of body fat is overwhelmed by the cardiovascular risks of higher body weight. For those with higher BMI, cold-induced stress—which raises blood pressure and thickens blood viscosity—is significantly amplified, increasing cardiovascular risk despite any insulating effect.

The researchers were surprised by the impact of extreme precipitation—an understudied area. Unlike extreme temperatures, extreme precipitation did not exhibit a continuous, regular spatial pattern at the regional level, yet it showed significant adverse effects on CVD at the individual level.

Co-investigator Liangwen Zhang, Ph.D., notes, “This discrepancy may stem from the fact that the multi-scale geographic analysis emphasizes average regional effects, while the health impacts of extreme precipitation are diluted by differences in individual exposure and regional protective measures, such as urban-rural differences in drainage infrastructure and health care accessibility.

“Unlike the cumulative effects of extreme temperatures, precipitation ECEs are primarily associated with single, short-duration events (heavy short-term rainfall) with scattered spatial distribution. The observed CVD risk may be attributed to abrupt changes in temperature and humidity caused by heavy precipitation.”

The investigators emphasize that further research into extreme precipitation events is needed to elucidate their impact on heart health.

The study highlights the following strategies for policymakers to protect vulnerable populations during extreme climate events:

1. Prioritizing climate-vulnerable regions by linking meteorological alerts to health care networks, alerting high-risk groups and pre-positioning resources.
2. Offering weight management, air purification support, and simplified health education for high-risk subgroups.
3. Establishing alliances to share resources between high-capacity areas and hotspots and prioritizing CVD prevention funding in fast-urbanizing regions.
4. Expanding green spaces and upgrading cooling/heating infrastructure.
5. Tracking climate and CVD data to dynamically adjust policies.

“Climate change is not just an environmental issue; it is a key factor affecting population health, for which urgent interdisciplinary action is required,” concludes co-investigator Linjiang Wei, Ph.D. “Older adults are more vulnerable due to age-related physiological decline and underlying diseases.”