Apparent temperature associated mortality risk and effect modification by sex and education in an elderly cohort of Hong Kong Chinese

Abstract

BACKGROUND: Few studies have examined the effects of thermal stress on mortality and susceptibility of socio-economic subgroups. OBJECTIVES: To assess associations between apparent temperature and mortality and their possible modification by sex and education. METHODS: We used a matched case-control design to assess short-term effects on mortality of apparent temperature, as a time-dependent variable, in a cohort of 66,820 persons aged 65 years or older recruited in 1998-2001 and followed up until 2009. The cases (14,446 deaths) were matched with controls by duration of exposure with adjustment for particulate and baseline covariates. Further, associations for gender and education subgroups were analyzed. RESULTS: In cool season, for a 1oC decrease in moving average of current day and previous 6 days, apparent temperature was associated with 2.0% (95% CI:0.9, 3.0), 2.8% (0.8, 4.8) and 4.0% (1.3, 6.7) increased risk for all-cause, cardiovascular and respiratory mortality, respectively, which were higher in females than males. The increased risks were significant (p<0.05) in subjects with primary education 2.6% (1.0, 4.1) for all-cause mortality and 4.1% (1.0, 7.1) for cardiovascular mortality; with no formal education 4.9% (1.4, 8.3) for respiratory mortality; but were not significant in those with secondary education or above. CONCLUSIONS: In cool season, decrease in apparent temperature was associated with increase in risk of all-cause and cardiorespiratory mortality, with females more susceptible to the effects than males. But during warm season, the effects of apparent temperature were not evident for the whole and subgroups.