日前，美国哈佛大学公共卫生学院的研究者报告说，夏季最高温度与最低温度之差如果显著拉大，有可能提高老年慢性病患者的死亡率。相关论文发表在美国《国家科学院院刊》（PNAS）上。
报告指出，研究人员利用美国“医疗保健”系统在1985年至2006年间收集的数据，追踪研究约370万名65岁以上慢性病患者的长期健康状况。排除其他影响因素后，研究人员发现，在这些老人居住的135个城市中，如遇上夏季温差变化较大的年份，老人的死亡率会随之升高。
总体而言，夏季温差每升高1摄氏度，老年慢性病患者的死亡率平均增加2.8%至4%，其中糖尿病患者死亡率增加4%，心脏病患者的死亡率增加3.8%，这一几率在慢性肺病和心衰患者中则分别增加3.7%和2.8%。
科学界近年来预测，气候变化不仅会提升全球气温，而且会扩大夏季气温变化幅度，特别是在中纬度地区。这项新研究结果说明，这种温差变化可能引起公共卫生问题。
报告作者之一、哈佛大学教授乔尔·施瓦茨说，人们不容易适应异常的气温变化，随着人口老化，糖尿病等慢性病的患病比例逐渐增高，气候变化导致更多异常气温波动，这类公共卫生问题可能变得越发突出。（生物谷Bioon.com）
doi:10.1073/pnas.1113070109
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Summer temperature variability and long-term survival among elderly people with chronic disease
Zanobetti, Antonella; O'Neill, Marie S.; Gronlund, Carina J.; Schwartz, Joel D.
Time series studies show that hot temperatures are associated with increased death rates in the short term. In light of evidence of adaptation to usual temperature but higher deaths at unusual temperatures, a long-term exposure relevant to mortality might be summertime temperature variability, which is expected to increase with climate change. We investigated whether the standard deviation (SD) of summer (June–August) temperatures was associated with survival in four cohorts of persons over age 65 y with predisposing diseases in 135 US cities. Using Medicare data (1985–2006), we constructed cohorts of persons hospitalized with chronic obstructive pulmonary disease, diabetes, congestive heart failure, and myocardial infarction. City-specific yearly summer temperature variance was linked to the individuals during follow-up in each city and was treated as a time-varying exposure. We applied a Cox proportional hazard model for each cohort within each city, adjusting for individual risk factors, wintertime temperature variance, yearly ozone levels, and long-term trends, to estimate the chronic effects on mortality of long-term exposure to summer temperature SD, and then pooled results across cities. Mortality hazard ratios ranged from 1.028 (95% confidence interval, 1.013– 1.042) per 1 °C increase in summer temperature SD for persons with congestive heart failure to 1.040 (95% confidence interval, 1.022–1.059) per 1 °C increase for those with diabetes. Associations were higher in elderly persons and lower in cities with a higher percentage of land with green surface. Our data suggest that long-term increases in temperature variability may increase the risk of mortality in different subgroups of susceptible older populations.
