title: Global Association of Cold Spells and Adverse Health Effects: A Systematic Review and Meta-Analysis.
abstract: BACKGROUND
  There is substantial evidence that mortality increases in low temperatures. Less is known about the role of prolonged cold periods denoted as cold spells.
  
  
  OBJECTIVE
  We conducted the first systematic review and meta-analysis to summarize the evidence on the adverse health effects of cold spells in varying climates.
  
  
  METHODS
  Four databases (Ovid Medline, PubMed, Scopus, Web of Science) were searched for all years and languages available. "Cold spell" was defined as an event below a temperature threshold lasting for a minimum duration of 2 days. Of 1,527 identified articles, 26 satisfied our eligibility criteria for the systematic review, and 9 were eligible for meta-analyses. The articles were grouped by the three main study questions into Overall-effect Group, Added-effect Group, and Temperature-change-effect Group.
  
  
  RESULTS
  Based on random-effects models in the meta-analyses, cold spells were associated with increased mortality from all or all nonaccidental causes (summary rate ratio = 1.10; 95% CI: 1.04, 1.17 based on 9 estimates from five studies), cardiovascular diseases (1.11; 95% CI: 1.03, 1.19; 12 estimates from eight studies), and respiratory diseases (1.21; 95% CI: 0.97, 1.51; 8 estimates from four studies). Estimated associations were stronger for people ≥ 65 years of age (1.06; 95% CI: 1.00, 1.12) than for people 0-64 years of age (1.01; 95% CI: 1.00, 1.03). Study-specific effect estimates from a limited number of studies suggested an increased morbidity related to cold spells, but it was not possible to quantitatively summarize the evidence.
  
  
  CONCLUSIONS
  Cold spells are associated with increased mortality rates in populations around the world. The body of evidence suggests that cold spells also have other adverse health effects. There was substantial heterogeneity among the studies, which should be taken into account in the interpretation of the results.
  
  
  BACKGROUND
  Ryti NR, Guo Y, Jaakkola JJ. 2016. Global association of cold spells and adverse health effects: a systematic review and meta-analysis. Environ Health Perspect 124:12-22; http://dx.doi.org/10.1289/ehp.1408104.
authors.affiliation: Center for Environmental and Respiratory Health Research, Faculty of Medicine, University of Oulu, Oulu, Finland.
authors.forename: Niilo R I
authors.initials: NR
authors.lastname: Ryti
authors.forename: Yuming
authors.initials: Y
authors.lastname: Guo
authors.forename: Jouni J K
authors.initials: JJ
authors.lastname: Jaakkola
mesh_terms: D002318:Cardiovascular Diseases / Q000209:etiology / Q000401:mortality; D003080:Cold Temperature; D016208:Databases, Factual; D006801:Humans; D008962:Models, Theoretical; D011634:Public Health