Objective To explore the effects of extreme air temperatures on the mortality from circulatory diseases and the susceptibility of different populations in Hefei, China.

Methods The daily data on meteorological factors, air pollutants, and mortality due to circulatory diseases in Hefei from 2016 to 2021 were collected. A distributed lag nonlinear model combined with a generalized additive model was applied to evaluate the effects of extreme air temperatures on the total deaths from circulatory diseases as well as the lag effects and cumulative effects on the deaths from major circulatory diseases in populations of different sexes and ages. In comparison with the median of daily average temperature (17.7℃), the relative risk (RR) at extreme temperatures was calculated.

Results Extreme air temperatures significantly affected the deaths from circulatory diseases in Hefei. Extreme low temperatures had long-lasting lag effects on the deaths from circulatory diseases, reaching the highest at lag 4 (RR=1.067, 95% confidence intervalCI: 1.039-1.095); extreme low temperatures significantly increased the death risk for all populations. At extreme high temperatures, the effect on the deaths from circulatory diseases peaked on the same day (RR=1.088, 95%CI: 1.020-1.160) with a short duration; the effects peaked on the same day for people over 65 years old, females, and people with cerebrovascular diseases, which were statistically significant, with no significant differences for other populations. For different populations, the cold effects of extreme temperatures were all higher than the heat effects. Low temperatures posed a significantly higher death risk for people < 65 years old than those ≥ 65 years old, while high temperatures produced the opposite effect. The cold effect and heat effect for females were both greater than those for males. The cold effect and heat effect were also greater in people with cerebrovascular disease than in those with ischemic heart disease.

Conclusion Extreme air temperatures in Hefei can significantly increase the death risk due to circulatory diseases, and the cold effect is greater than the heat effect. The susceptibility to the heat and cold effects varies among different populations.