title: Relationship between tap water hardness, magnesium, and calcium concentration and mortality due to ischemic heart disease or stroke in The Netherlands.
abstract: BACKGROUND
  Conflicting results on the relationship between the hardness of drinking water and mortality related to ischemic heart disease (IHD) or stroke have been reported.
  
  
  OBJECTIVE
  We investigated the possible association between tap water calcium or magnesium concentration and total hardness and IHD mortality or stroke mortality.
  
  
  METHODS
  In 1986, a cohort of 120,852 men and women aged 5569 years provided detailed information on dietary and other lifestyle habits. Follow-up for mortality until 1996 was established by linking data from the Central Bureau of Genealogy and Statistics Netherlands. We calculated tap water hardness for each postal code using information obtained from all pumping stations in the Netherlands. Tap water hardness was categorized as soft [< 1.5 mmol/L calcium carbonate (CaCO3)], medium hard (1.62.0 mmol/L CaCO3), and hard (> 2.0 mmol/L CaCO3). The multivariate case-cohort analysis was based on 1,944 IHD mortality and 779 stroke mortality cases and 4,114 subcohort members.
  
  
  RESULTS
  For both men and women, we observed no relationship between tap water hardness and IHD mortality [hard vs. soft water: hazard ratio (HR) = 1.03; 95% confidence interval (CI), 0.851.28 for men and HR = 0.93; 95% CI, 0.711.21 for women) and stroke mortality (hard vs. soft water HR = 0.90; 95% CI, 0.661.21 and HR = 0.86; 95% CI, 0.621.20, respectively). For men with the 20% lowest dietary magnesium intake, an inverse association was observed between tap water magnesium intake and stroke mortality (HR per 1 mg/L intake = 0.75; 95% CI, 0.610.91), whereas for women with the 20% lowest dietary magnesium intake, the opposite was observed.
  
  
  CONCLUSIONS
  We found no evidence for an overall significant association between tap water hardness, magnesium or calcium concentrations, and IHD mortality or stroke mortality. More research is needed to investigate the effect of tap water magnesium on IHD mortality or stroke mortality in subjects with low dietary magnesium intake.
authors.affiliation: Maastricht University, GROW--School for Oncology and Developmental Biology, Department of Epidemiology, Maastricht, The Netherlands. Lina.Leurs@EPID.unimaas.nl
authors.forename: Lina J
authors.initials: LJ
authors.lastname: Leurs
authors.forename: Leo J
authors.initials: LJ
authors.lastname: Schouten
authors.forename: Margreet N
authors.initials: MN
authors.lastname: Mons
authors.forename: R Alexandra
authors.initials: RA
authors.lastname: Goldbohm
authors.forename: Piet A
authors.initials: PA
authors.lastname: van den Brandt
mesh_terms: D000368:Aged; D002118:Calcium / Q000032:analysis*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008274:Magnesium / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000453:epidemiology / Q000209:etiology / Q000401:mortality*; D009426:Netherlands / Q000453:epidemiology; D020521:Stroke / Q000453:epidemiology / Q000209:etiology / Q000401:mortality*; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014881:Water Supply / Q000032:analysis* / Q000592:standards
chemical_list: D014874:Water Pollutants, Chemical; D014867:Water; D008274:Magnesium; D002118:Calcium