Extreme heat exposure was associated with modest acute reductions in blood pressure (BP) among adults receiving care at community health centers (CHCs), with slightly larger reductions among older adults, according to a cross-sectional study published Sept. 10 in JAMA Network Open. The findings may be relevant to clinical BP measurement and cardiovascular risk assessment in outpatient settings.

Brenda M. McGrath, PhD, et al., analyzed electronic health record data from OCHIN, a national network of 2,554 CHCs in 40 U.S. states, collected from June through August in 2019 through 2023. Data were analyzed from October 2025 to April 2026. Participants were adults with ambulatory encounters that included BP measurements.

Same-day and short-term extreme heat exposure were assessed using the GridEX dataset linked to clinic locations; extreme heat was defined as temperatures exceeding location-specific thresholds. Associations were estimated using mixed-effects models adjusted for age, sex, race and ethnicity, hypertension and medication status, comorbidities, year and geographic region. Effect modification by age, hypertension and medication status, as well as cumulative associations across an eight-day window, also were assessed.

The study included nearly 4.3 million ambulatory encounters. Most encounters (81%) were among patients without a hypertension diagnosis. Mean age was 48 years; 63% of participants were women and 28% were non-Hispanic White.

The primary outcomes were systolic and diastolic BP recorded during ambulatory visits. Same-day extreme heat exposure was associated with lower systolic BP (−0.7 mm Hg) and diastolic BP (−0.3 mm Hg). Decreases were larger among adults ≥65 years vs. those <65 years (systolic: −1.1 mm Hg vs. −0.6 mm Hg; diastolic: −0.8 mm Hg vs. −0.3 mm Hg).

Hypertension status modified the association between extreme heat exposure and systolic BP (p=0.003), but not diastolic BP (p=0.84). BP reductions were greatest on the day of heat exposure and the next day, diminished by day 3, and cumulatively decreased over seven days by 0.8 mm Hg for systolic BP and 0.5 mm Hg for diastolic BP.

The findings "highlight the complexity of cardiovascular responses to extreme heat exposure in everyday community settings," the authors write. They add that the results underscore the need to consider temporal scale, age and clinical and community context when assessing heat-related cardiovascular risk, and suggest that acute BP changes are unlikely to be the primary pathway linking extreme heat to cardiovascular risk.