title: Association between winter season and risk of death from cardiovascular diseases: a study in more than half a million inpatients in Beijing, China.
abstract: BACKGROUND
  Seasonal associations of cardiovascular mortality have been noted in most populations of European origin years ago, but are not well evaluated in Asian populations recently.
  
  
  METHODS
  Utilizing the electronic Hospitalization Summary Reports (HSRs) from 32 top-ranked hospitals in Beijing, China, we evaluated the association between winter season and the risk of cardiovascular death among hospitalized individuals. General additive models and logistic regression models were adjusted for confounding factors.
  
  
  RESULTS
  Older patients who were admitted to the hospital in the winter months (January, February, November and December) had a death risk that was increased by approximately 30% to 50% (P < 0.01) over those who were admitted in May. However, younger patients did not seem to experience the same seasonal variations in death risk. The excess winter deaths among older patients were associated with ischemic heart disease (RR = 1.22; 95% CI 1.13 to 1.31), pulmonary heart disease (RR = 1.42; 95% CI 1.10 to 1.83), cardiac arrhythmias (RR = 1.67; 95% CI 1.36 to 2.05), heart failure (RR = 1.30; 95% CI 1.09 to 1.54), ischemic stroke (RR = 1.30; 95% CI 1.17 to 1.43), and other cerebrovascular diseases (RR = 1.78; 95% CI 1.40 to 2.25). The risks of mortality were higher in winter months than in the month of May, regardless of the presence or absence of respiratory disease.
  
  
  CONCLUSIONS
  Winter season was associated with a substantially increased risk of cardiovascular death among older Chinese cardiovascular inpatients.
authors.forename: Beibei
authors.initials: B
authors.lastname: Xu
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.forename: Naifang
authors.initials: N
authors.lastname: Su
authors.forename: Guilan
authors.initials: G
authors.lastname: Kong
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Bao
authors.forename: Jiong
authors.initials: J
authors.lastname: Li
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.forename: Xiemin
authors.initials: X
authors.lastname: Ma
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Medical Informatics Center, Peking University, 38 Xueyuan Rd, Haidian District, 100191, Beijing, China. yugp@bjmu.edu.cn.
authors.forename: Guo-Pei
authors.initials: GP
authors.lastname: Yu
authors.forename: Lueping
authors.initials: L
authors.lastname: Zhao
mesh_terms: D000328:Adult; D000368:Aged; D002318:Cardiovascular Diseases / Q000208:ethnology* / Q000401:mortality*; D002681:China / Q000208:ethnology; D005260:Female; D006760:Hospitalization / Q000639:trends*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012621:Seasons