High diurnal temperature range and mortality: Effect modification by individual characteristics and mortality causes in a case-only analysis.

Background: Consistent evidence has shown that high diurnal temperature range (DTR) is associated with excess mortality, but little is known about the subgroups in the association. We aimed to identify the effect modifiers, including individual characteristics and specific mortality causes, of the association in a high plateau region with large DTR and extensive ethnic minorities in China.

Methods: We conducted a case-only analysis in 77,319 non-accidental deaths in Yuxi during 2007-2014, and evaluated the effect modifiers of the association of high DTR exposure and mortality. All non-accidental deaths were divided into cardiovascular, respiratory, and "other" causes. High DTR days were defined as ≥ 90th percentile of DTR.

Results: Risk of mortality on high DTR days was associated with age 75-84 years (odds ratio 1.07; 95% confidence interval 1.01-1.14) and ≥ 85 years (1.16; 1.08-1.24) as compared with age ≤ 64 years. The risk of the association was less for the Dai ethnic minority than Chinese Han (0.85; 0.75-0.96). Farmers (1.08; 1.03-1.14) and people with hypertension (1.09; 1.02-1.16) showed greater risk of dying on high DTR days than non-farmers and people without hypertension, respectively. Compared with "other" mortality causes, the risk was greater with cardiovascular causes (1.09; 1.04-1.15), notably ischemic heart disease (1.16; 1.08-1.25) and myocardial infarction (1.18; 1.08-1.29) in heart disease (1.11; 1.04-1.17), and ischemic stroke (1.17; 1.06-1.28) in stroke deaths (1.09; 1.03-1.15), as well as chronic bronchitis (1.22; 1.11-1.33) and chronic obstructive pulmonary disease (1.12; 1.05-1.20) in respiratory deaths (1.11; 1.04-1.18).

Conclusions: Individual characteristics and specific mortality causes can modify the association of high DTR and mortality. This knowledge may help in better targeting the vulnerable populations and developing more effective intervention strategies.