title: Colder-to-warmer changes in children's blood lead concentrations are related to previous blood lead status: results from a systematic review of prospective studies.
abstract: OBJECTIVE
  To estimate the extent of changes in mean BLLs from colder to warmer months, in children aged 1-5 years with different status of lead in colder months.
  
  
  METHODS
  We performed a systematic review using an in-house algorithm developed in MEDLINE, EMBASE, Web of Science, and CINHAL. Search was performed between November 2012 and July 2013, and data evaluation and extraction were subsequently conducted. The mean BLLs observed in the warmer months was divided by the one observed in the colder months to obtain the warmer-to-colder ratio (WCR). Study-specific WCRs were pooled using the fixed-effects method of Mantel-Haenszel to estimate the combined WCR.
  
  
  RESULTS
  From 4040 papers initially identified, eight cohort studies were considered relevant for inclusion. The combined WCR was inversely related to the BLLs observed during colder months. The values were 1.25 (95% CI: 0.90-1.60), 1.06 (95% CI: 0.92-1.19), and 0.95 (95% CI: 0.51-1.39) for children showing baseline BLLs of <10μgdL(-1), 10-20μgdL(-1)and ≥20μgdL(-1), respectively. The combined WCR was influenced neither by children's age nor place/date of study.
  
  
  CONCLUSIONS
  The extent of the summer increase in BLLs depends on the BLLs in the colder months.
authors.affiliation: Population Health and Optimal Health Practices Research Unit, Research Center of CHU of Quebec, Laval University, Quebec, QC, Canada; Department of Social and Preventive Medicine, Faculty of Medicine, Laval University, Quebec, QC, Canada. Electronic address: Gerard.Ngueta@crchuq.ulaval.ca.
authors.forename: Gerard
authors.initials: G
authors.lastname: Ngueta
authors.affiliation: Population Health and Optimal Health Practices Research Unit, Research Center of CHU of Quebec, Laval University, Quebec, QC, Canada.
authors.forename: Catherine
authors.initials: C
authors.lastname: Gonthier
authors.affiliation: Population Health and Optimal Health Practices Research Unit, Research Center of CHU of Quebec, Laval University, Quebec, QC, Canada; Department of Social and Preventive Medicine, Faculty of Medicine, Laval University, Quebec, QC, Canada; National Public Health Institute of Quebec, QC, Canada.
authors.forename: Patrick
authors.initials: P
authors.lastname: Levallois
mesh_terms: D002648:Child; D002675:Child, Preschool; D006801:Humans; D007854:Lead / Q000097:blood*; D011446:Prospective Studies; D012621:Seasons
chemical_list: D007854:Lead
keywords: Blood lead levels; Children; Prospective studies; Season