Background Diurnal temperature range (DTR) is closely associated with cardiovascular health in the elderly, but there is a lack of research on the relationship between DTR and ischemic heart disease (IHD) in the elderly.

Objective To investigate the effect of DTR on daily hospital admissions for IHD in people 65 years and older in Wuhan.

Methods The study obtained data on elderly inpatients with IHD from all secondary and tertiary hospitals in Wuhan between January 1, 2017 and December 31, 2018, along with synchronous meteorological and air pollution data. Daily DTR was calculated as the difference between the maximum and minimum temperatures in a day. We employed distributed lag nonlinear models based on quasi-Poisson distribution to analyze the association between DTR and hospitalization risk in individuals aged 60 years and above. We assessed the extreme effects of DTR by selected DTR percentiles (the 1st percentile, P₁: 1.8 ℃; the 5th percentile, P₅: 2.9 ℃; the 95th percentile, P₉₅: 14.3 ℃; and the 99th percentile, P₉₉: 16.2 ℃) on hospitalization for IHD in the elderly population. Additionally, we conducted stratified analyses by gender, age (60-74 years and ≥75 years) and different subtypes (acute IHD and chronic IHD) to investigate the effects of DTR on hospitalizations for IHD across different genders, ages, and subtypes.

Results This study included a total of 64212 first-time IHD hospitalizations among individuals aged 65 years and above in Wuhan from 2017 to 2018. The results showed a "J"-shaped exposure-response relationship between DTR and the cumulative risk of IHD hospitalization with a lag of 7 d; the optimal DTR was 5.0 ℃, and as DTR increased or the lag time lengthened, the risk of hospitalization for IHD in the elderly population increased. Extremely high DTR (P₉₉: 16.2 ℃) had a significant impact on the day of exposure (lag 0), with a cumulative RR of 1.58 (95%CI: 1.25, 1.99) at a lag of 7 d. The overall effects of DTR on IHD for different genders, ages, and subtypes of IHD exhibited similar patterns to the effects for overall population. High DTR had a significantly higher impact on hospitalization for chronic IHD (RR=1.46, 95%CI: 1.20, 1.79), compared to acute IHD (RR=1.29, 95%CI: 1.04, 1.61). At a cumulative lag of 7 d, elderly individuals aged 60-74 (RR=1.78, 95% CI: 1.30, 2.42) were more affected by high DTR in terms of IHD hospitalizations compared to those aged ≥75 (RR=1.35, 95% CI: 1.08, 1.70).

Conclusion High DTR significantly increases the risk of hospitalization for IHD among elderly individuals. The effect of high DTR is particularly pronounced in patients with chronic IHD and elderly individuals aged 60–74 years.