title: Effect of water hardness on cardiovascular mortality: an ecological time series approach.
abstract: BACKGROUND
  Numerous studies have suggested an inverse relationship between drinking water hardness and cardiovascular disease. However, the weight of evidence is insufficient for the WHO to implement a health-based guideline for water hardness. This study followed WHO recommendations to assess the feasibility of using ecological time series data from areas exposed to step changes in water hardness to investigate this issue.
  
  
  METHODS
  Monthly time series of cardiovascular mortality data, subdivided by age and sex, were systematically collected from areas reported to have undergone step changes in water hardness, calcium and magnesium in England and Wales between 1981 and 2005. Time series methods were used to investigate the effect of water hardness changes on mortality.
  
  
  RESULTS
  No evidence was found of an association between step changes in drinking water hardness or drinking water calcium and cardiovascular mortality. The lack of areas with large populations and a reasonable change in magnesium levels precludes a definitive conclusion about the impact of this cation. We use our results on the variability of the series to consider the data requirements (size of population, time of water hardness change) for such a study to have sufficient power. Only data from areas with large populations (>500,000) are likely to be able to detect a change of the size suggested by previous studies (rate ratio of 1.06).
  
  
  CONCLUSIONS
  Ecological time series studies of populations exposed to changes in drinking water hardness may not be able to provide conclusive evidence on the links between water hardness and cardiovascular mortality unless very large populations are studied. Investigations of individuals may be more informative.
authors.affiliation: School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK. i.lake@uea.ac.uk
authors.forename: I R
authors.initials: IR
authors.lastname: Lake
authors.forename: L
authors.initials: L
authors.lastname: Swift
authors.forename: L A
authors.initials: LA
authors.lastname: Catling
authors.forename: I
authors.initials: I
authors.lastname: Abubakar
authors.forename: C E
authors.initials: CE
authors.lastname: Sabel
authors.forename: P R
authors.initials: PR
authors.lastname: Hunter
mesh_terms: D000368:Aged; D002118:Calcium / Q000032:analysis*; D002318:Cardiovascular Diseases / Q000453:epidemiology / Q000401:mortality*; D004326:Drinking; D004739:England / Q000453:epidemiology; D004784:Environmental Monitoring / Q000379:methods*; D062665:Epidemiological Monitoring; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008274:Magnesium / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D014798:Vital Statistics; D014852:Wales / Q000453:epidemiology; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D008274:Magnesium; D002118:Calcium