Extreme heat exposure was associated with modest acute reductions in blood pressure among adults receiving care at community health centers, with slightly larger reductions among older adults.
Key Findings
Results
Same-day extreme heat exposure was associated with small but statistically significant reductions in both systolic and diastolic blood pressure.
Systolic BP reduction: -0.7 mm Hg (95% CI, -0.8 to -0.6 mm Hg)
Diastolic BP reduction: -0.3 mm Hg (95% CI, -0.3 to -0.2 mm Hg)
Analysis based on 4,221,866 ambulatory encounters across summer months (June–August) from 2019 to 2023
Mixed-effects models were used with patient- and facility-level random intercepts, adjusting for age, sex, race and ethnicity, hypertension and medication status, comorbidities, year, and geographic region
Results
Adults aged 65 years or older showed larger blood pressure reductions associated with extreme heat exposure compared to adults under 65.
Systolic BP reduction in adults ≥65 years: -1.1 mm Hg (95% CI, -1.3 to -0.9 mm Hg) vs. -0.6 mm Hg (95% CI, -0.7 to -0.5 mm Hg) in adults <65 years; interaction P < .001
Diastolic BP reduction in adults ≥65 years: -0.8 mm Hg (95% CI, -1.0 to -0.6 mm Hg) vs. -0.3 mm Hg (95% CI, -0.3 to -0.2 mm Hg) in adults <65 years; interaction P < .001
Effect modification by age was statistically significant for both systolic and diastolic BP outcomes
Results
Hypertension status modified the association between extreme heat exposure and systolic BP but not diastolic BP.
Omnibus interaction P = .003 for systolic BP by hypertension status
Omnibus interaction P = .84 for diastolic BP by hypertension status
Most encounters (81%) were for patients without a hypertension diagnosis
Results
In distributed lag analyses, blood pressure reductions associated with extreme heat peaked on the day of exposure and the following day and attenuated by day 3.
BP reductions were largest at lag 0 (day of exposure) and lag 1 (following day), then attenuated by day 3
Minimal cumulative differences were observed thereafter
Cumulative difference across lags 0 through 7: -0.8 mm Hg (95% CI, -1.0 to -0.6 mm Hg) for systolic BP
Cumulative difference across lags 0 through 7: -0.5 mm Hg (95% CI, -0.6 to -0.4 mm Hg) for diastolic BP
An 8-day exposure window was assessed using distributed lag nonlinear models
Methods
The study population was large and diverse, drawn from a national network of community health centers across 40 US states.
Data came from 2,554 community health centers (CHCs) across 40 US states
Total encounters analyzed: 4,221,866 ambulatory encounters
Cohort mean (SD) age: 47.6 (17.0) years; 63% female
Electronic health record data were used from summer months (June through August) of 2019 to 2023
Extreme heat was defined using the GridEX dataset at 500×500 m spatial resolution linked to clinic locations, operationalized as days exceeding location-specific thresholds
Conclusions
The authors concluded that extreme heat exposure may be relevant for clinical BP measurement and cardiovascular risk assessment in outpatient settings.
Findings described as reflecting 'physiologic responses to heat'
The study was cross-sectional, limiting causal inference
The authors specifically noted relevance for 'clinical BP measurement and cardiovascular risk assessment in outpatient settings'
Data were analyzed October 2025 to April 2026
What This Means
This research suggests that on days of extreme heat, patients visiting community health centers tend to have slightly lower blood pressure readings than on non-extreme-heat days. The study analyzed over 4 million clinic visits across the United States between 2019 and 2023 and found that same-day extreme heat was linked to a reduction of about 0.7 points in systolic (top number) blood pressure and 0.3 points in diastolic (bottom number) blood pressure. These reductions were modest but consistent across a very large and diverse patient population.
The effect was somewhat larger among adults aged 65 and older, who showed roughly double the blood pressure reduction compared to younger adults during extreme heat. The impact was also short-lived: blood pressure reductions were greatest on the day of heat exposure and the next day, largely disappearing by the third day. Whether a patient had been diagnosed with hypertension (high blood pressure) affected the systolic but not the diastolic response to heat.
This research suggests that clinicians and patients should be aware that blood pressure readings taken during extreme heat events may be somewhat lower than usual, potentially reflecting the body's natural response to cooling itself (such as blood vessels widening). This could be relevant when interpreting blood pressure measurements or making decisions about cardiovascular health management during hot weather periods. The findings add to a growing body of evidence linking extreme heat to meaningful physiological changes in the body.
McGrath B, Georgescu J, Fard P, Gold R, Heintzman J, Patel C, et al.. (2026). Extreme Heat Exposure and Blood Pressure in Community Health Center Patients.. JAMA network open. https://doi.org/10.1001/jamanetworkopen.2026.33066