Abstract

Background

Although seasonal variations in mortality have been recognized for millennia, the role of temperature remains unclear. We aimed to assess seasonal variation in mortality and to examine the contribution of temperature.

Methods

We compiled daily data on all-cause, cardiovascular and respiratory mortality, temperature and indicators on location-specific characteristics from 719 locations in tropical, dry, temperate and continental climate zones. We fitted time-series regression models to estimate the amplitude of seasonal variation in mortality on a daily basis, defined as the peak-to-trough ratio (PTR) of maximum mortality estimates to minimum mortality estimates at day of year. Meta-analysis was used to summarize location-specific estimates for each climate zone. We estimated the PTR with and without temperature adjustment, with the differences representing the seasonal effect attributable to temperature. We also evaluated the effect of location-specific characteristics on the PTR across locations by using meta-regression models.

Results

Seasonality estimates and responses to temperature adjustment varied across locations. The unadjusted PTR for all-cause mortality was 1.05 [95% confidence interval (CI): 1.00–1.11] in the tropical zone and 1.23 (95% CI: 1.20–1.25) in the temperate zone; adjusting for temperature reduced the estimates to 1.02 (95% CI: 0.95–1.09) and 1.10 (95% CI: 1.07–1.12), respectively. Furthermore, the unadjusted PTR was positively associated with average mean temperature.

Conclusions

This study suggests that seasonality of mortality is importantly driven by temperature, most evidently in temperate/continental climate zones, and that warmer locations show stronger seasonal variations in mortality, which is related to a stronger effect of temperature.

中文翻译：

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死亡率的季节性变化和温度的作用：一项多国多城市研究

 抽象的

 背景

尽管几千年来人们已经认识到死亡率的季节性变化，但温度的作用仍不清楚。我们的目的是评估死亡率的季节性变化并研究温度的影响。

 方法

我们收集了热带、干燥、温带和大陆性气候区 719 个地点的全因死亡率、心血管和呼吸道死亡率、温度和特定地点特征指标的每日数据。我们拟合了时间序列回归模型来估计每日死亡率季节性变化的幅度，定义为一年中某一天最高死亡率估计值与最低死亡率估计值的峰谷比（PTR）。荟萃分析用于总结每个气候带的特定地点的估计。我们估计了有和没有温度调整的 PTR，差异代表了温度造成的季节性影响。我们还使用元回归模型评估了特定位置特征对跨位置 PTR 的影响。

 结果

季节性估计和对温度调整的反应因地点而异。全因死亡率未经调整的 PTR 在热带地区为 1.05 [95% 置信区间 (CI)：1.00–1.11]，在温带地区为 1.23（95% CI：1.20–1.25）；根据温度进行调整后，估计值分别降至 1.02（95% CI：0.95–1.09）和 1.10（95% CI：1.07–1.12）。此外，未调整的 PTR 与平均温度呈正相关。

 结论

这项研究表明，死亡率的季节性在很大程度上是由温度驱动的，在温带/大陆气候区最为明显，而较温暖的地区死亡率的季节性变化更大，这与温度的更强影响有关。