Objective To explore the relationship between daily average temperature and mortality in Lanzhou, and evaluate the temperature-related risk of non-accidental, cardiovascular, and respiratory mortalities.
Methods Residents' death, temperature, and air pollution data in Lanzhou were collected from 2014 to 2017. A distributed lag nonlinear model was applied to explore the lag effect and cumulative effect of temperature on selected health outcomes with adjustments of long-term trends, seasonal effects, relative humidity, and air pollutants. We chose 21 d as the maximum lag time. RR values of P5 (-4.2℃) and P95 (-25.5℃) versus P50 of daily mean temperature were calculated to evaluate the cumulative effects of lag 0, 0-3, 0-7, 0-14, and 0-21 days, respectively.
Results From January 1, 2014 to December 31, 2017, the daily average number of non-accidental deaths in Lanzhou was 39, of which 17 were caused by cardiovascular diseases and 5 by respiratory diseases, respectively. The daily mean concentrations of atmospheric pollutants PM10, SO2, and NO2 over the same period were 123.54, 21.91, and 49.88 μg/m3, respectively. The daily mean temperature and relative humidity were 11.35℃ and 50.76%, respectively. The effect of daily average temperature on the mortality of non-accidental, cardiovascular, or respiratory diseases each presented a J shaped curve. Heat mainly imposed acute short-term effect both on non-accidental and cardiovascular mortalities, and the maximum RRs of heat-related death occurred at 29℃ with 0 d lag, which were 1.07 (95%CI:1.02-1.12) and 1.09 (95%CI:1.02-1.18), respectively; respiratory mortality was not sensitive to heat. Unlike heat, cold temperature showed a long lag effect on mortality, and the maximum RRs of cold temperature on non-accidental, cardiovascular, and respiratory mortalities all occurred at -12℃ with 21 d lag, which were 1.36 (95%CI:1.26-1.45), 1.34 (95%CI:1.22-1.50), and 1.45 (95%CI:1.22-1.72), respectively. With the median annual mean temperature (P50, 12.9℃) as a reference value, the cumulative effects of low temperature (P5, -4.2℃) on non-accidental mortality and cardiovascular diseases mortality were both strongest at lag 0-21 d, and the RR values were 1.15 (95%CI:1.07-1.23) and 1.16 (95%CI:1.04-1.28), respectively; the cumulative effect of high temperature (P95, 25.5℃) on non-accidental mortality was significant at both lag 0 and lag 0-3 d, and was strongest at lag 0-3 d with the RR of 1.11 (95%CI:1.02-1.20).
Conclusion High and low temperatures both increase the risk of selected mortalities with delayed effects in Lanzhou, and the effect of low temperature lasts longer than high temperature.
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