Heatwaves Above 38°C Linked to 3% Surge in Individual Heart Disease Risk for Middle-Aged Adults, New Longitudinal Study Finds

Study of 157 cities finds extreme heat increases CVD risk by 3% per day. Learn how BMI and pollution impact heart health during climate extremes.

By: AXL Media

Published: Apr 21, 2026, 4:09 AM EDT

Source: Information for this report was sourced from Elsevier

The Escalating Threat of Extreme Climate Events

As global temperatures continue to rise, extreme climate events (ECEs) are transitioning from environmental anomalies to primary public health crises. Researchers from Xiamen University utilized longitudinal data from 2015 to 2020 to track the cardiovascular health of middle-aged and older adults across nearly 160 urban centers. The study arrives at a critical juncture for China, which is projected to have an aging population of 400 million by 2035. Lead investigator Dr. Ya Fang noted that by integrating city-level and individual-level data, the team has successfully mapped how heatwaves, deep freezes, and extreme precipitation directly correlate with the prevalence of the world's leading cause of death.

Heatwaves and the Physics of Cardiovascular Strain

The most striking finding of the report is the impact of temperatures exceeding 38°C. At this threshold, the study found that each additional day of extreme heat is associated with 1,128 additional CVD cases per 100,000 people. On an individual basis, this translates to a 3.044% increase in heart disease risk per heat day. The researchers explained that above 38°C, the body’s standard cooling mechanism fails; instead of the body shedding heat into the environment, thermal energy flows from the atmosphere into the body. This reversal puts immense pressure on the heart to maintain core temperature, particularly for pre-retirees and smokers.

The Complex Role of BMI in Thermal Regulation

The investigation revealed a counterintuitive relationship between Body Mass Index (BMI) and temperature intensity. During extreme heatwaves above 38°C, a higher BMI was actually found to mitigate risk, as body fat acts as a physical barrier against external thermal penetration. Conversely, in extreme cold below -10°C, this insulating effect is completely overwhelmed. In freezing conditions, higher body weight amplifies cold-induced stress, which increases blood viscosity and blood pressure. Consequently, individuals with a high BMI are significantly more vulnerable to cardiovascular events during winter extremes than during summer heatwaves.