In 1,923 older adults from the Lung VITAL cohort measured at two spirometry sessions between 2010 and 2018, cumulative heat exposure over the preceding 7 days was independently associated with meaningfully lower lung function. Comparing 30°C versus 20°C mean daily temperature, FEV1 dropped by approximately 50 mL (95% CI: −96 to −4 mL) and FVC by nearly 90 mL (95% CI: −157 to −22 mL). Models were carefully adjusted for humidity, PM2.5, ozone, season, and social vulnerability — isolating temperature as a distinct driver.
These effect sizes deserve context. A 50–90 mL reduction in FEV1 and FVC is clinically modest for a healthy individual but potentially significant for someone with borderline or established COPD, where small functional losses can tip patients into symptomatic exacerbation or reduced exercise tolerance. Existing literature has robustly linked heat to respiratory hospitalizations and mortality, but the mechanistic pathway through acute airway inflammation, increased ventilation demand, and dehydration-induced airway narrowing has lacked direct spirometric confirmation in real-world cohorts — this study begins to fill that gap.
Limitations include the observational design (residual confounding remains possible), the restriction to older adults (median temperatures were moderate at 13.6°C, limiting extrapolation to tropical climates), and the reliance on home-address temperature assignment rather than personal exposure. Still, as climate change drives more frequent heat events, this is an incrementally important finding — suggesting that older adults, particularly those with pre-existing lung disease, may benefit from proactive heat-avoidance strategies and clinical monitoring during hot spells.