Extreme Heat Has Limited Impact on Blood Pressure: Study Shows
USA: Researchers have found in a new study that extreme heat was associated with modest short-term reductions in blood pressure. The findings suggest that, in routine outpatient settings, extreme heat has limited influence on blood pressure and is unlikely to affect individual cardiovascular risk assessment significantly.
The study, published in JAMA Network Open, was conducted by Brenda M. McGrath, OCHIN, Portland, Oregon, and colleagues. The researchers examined whether exposure to unusually high temperatures was associated with acute changes in blood pressure among adults receiving care at community health centers (CHCs) across the United States.
Extreme heat is known to place stress on the cardiovascular system, but its immediate impact on blood pressure during routine clinical care has been less clearly understood. To investigate this association, researchers analyzed electronic health record data from 2,554 community health centers across 40 US states, covering summer months from June through August between 2019 and 2023.
The analysis covered 4,221,866 adult outpatient encounters, with extreme heat exposure assessed using GridEX temperature data linked to clinic locations. Both same-day and short-term cumulative exposure were evaluated.
Models were adjusted for age, sex, race and ethnicity, hypertension, medication use, comorbidities, year, and geographic region, while also assessing whether age or hypertension modified the association.
Key findings:
- Same-day extreme heat exposure was associated with a 0.7 mm Hg reduction in systolic blood pressure and a 0.3 mm Hg reduction in diastolic blood pressure.
- The association was more pronounced among adults aged 65 years and older, who experienced a 1.1 mm Hg reduction in systolic BP compared with 0.6 mm Hg among younger adults.
- Diastolic BP decreased by 0.8 mm Hg among older adults, compared with 0.3 mm Hg among those younger than 65 years.
- Hypertension status modified the association with systolic BP but did not significantly alter the relationship with diastolic BP.
- In analyses examining exposure over eight days, blood pressure reductions were greatest on the day of extreme heat exposure and the following day, with the differences diminishing by the third day.
- Across the full eight-day period, cumulative reductions were approximately 0.8 mm Hg for systolic BP and 0.5 mm Hg for diastolic BP.
The BP reductions were small and unlikely to affect individual cardiovascular risk, though heat may cause measurable short-term physiological changes.
The researchers noted certain limitations: clinic-based heat exposure may not reflect patients’ actual exposure. Variations in routine BP measurement and healthcare attendance may have affected results. The study also could not assess specific antihypertensive drugs, while the low frequency of extreme-heat exposure limited within-patient comparisons.
Overall, extreme heat was linked to modest, short-term BP reductions, particularly in older adults, but these changes were unlikely to be clinically significant.
Reference:
McGrath BM, Georgescu J, Fard P, et al. Extreme Heat Exposure and Blood Pressure in Community Health Center Patients. JAMA Netw Open. 2026;9(9):e2633066. doi:10.1001/jamanetworkopen.2026.33066
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