The Effects of Intra‐Day Temperature Variability on Cause‐Specific Mortality: A Time‐Stratified Case‐Crossover Study in Chongqing, China

Abstract Although temperature variability (TV) has been linked to an increased mortality risk, the independent effect of intra‐day TV remains insufficiently understood. This study aimed to examine the association between intra‐day TV exposure and cause‐specific mortality in a Chinese population. We collected daily mortality data and meteorological variables from 2016 to 2022 in Jiulongpo District, Chongqing, China. A time‐stratified case‐crossover design combined with a conditional logistic regression model was used to assess the association between TV exposure and the risk of cause‐specific mortality. A natural spline function was used to derive the exposure‐response (E‐R) relationship between intra‐day TV and the percentage change in mortality risk. We recorded 47,189 all‐cause mortality cases, including 19,152 cardiovascular deaths and 8126 respiratory deaths. Overall, there was a positive association between intra‐day TV and mortality. Specifically, each 1°C increase in intra‐day TV 0–7 was associated with an increased risk of 5.20% (95% CI: 3.87%, 6.54%) for all‐cause mortality, 6.20% (95% CI: 4.14%, 8.31%) for cardiovascular mortality, and 9.24% (95% CI: 5.98%, 12.60%) for respiratory mortality. The E‐R curves for cardiovascular mortality were approximately linear, whereas all‐cause mortality at TV 0–1 to TV 0–5 and respiratory mortality at all lag windows exhibited nonlinear curves. The respiratory mortality curve rose steeply at lower TV levels and plateaued thereafter at higher levels. Intra‐day TV was positively associated with all‐causes, cardiovascular, and respiratory mortality, with the strongest association observed for respiratory mortality. Incorporating intra‐day TV into early warning systems may help reduce the mortality burden.