Academic journal article Environmental Health Perspectives

Relationship between Tap Water Hardness, Magnesium, and Calcium Concentration and Mortality Due to Ischemic Heart Disease or Stroke in the Netherlands

Academic journal article Environmental Health Perspectives

Relationship between Tap Water Hardness, Magnesium, and Calcium Concentration and Mortality Due to Ischemic Heart Disease or Stroke in the Netherlands

Article excerpt

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.

OBJECTIVES: 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 55-69 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 ([CaCO.sub.3])], medium hard (1.6-2.0 mmol/L [CaCO.sub.3]), and hard (> 2.0 mmol/L [CaCO.sub.3]). 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), 0.85-1.28 for men and HR = 0.93; 95% CI, 0.71-1-21 for women) and stroke mortality (hard vs. soft water HR = 0.90; 95% CI, 0.66-1.21 and HR = 0.86; 95% CI, 0.62-1.20, 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, 0.61-0.91), 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.

KEY WORDS: calcium, cohort study, ischemic heart disease, magnesium, stroke, water hardness. Environ Health Perspect 118:414-420 (2010). doi: l0.1289/ehp.0900782 available via http://dx.doi. org/ [Online 27 October 2009]

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The use of desalination of sea water as a source for drinking water is rapidly increasing worldwide (World Health Organization (WHO) 1979]. Because of this development, the WHO initiated a process to develop guidance for health and environmental aspects of water desalination, including recommendations on the mineral content of drinking water (WHO 2005). The identification of any population health effect associated with minerals in water may be of major importance when used on such a large scale. During the discussion about the potential health effects of nutrients in drinking water, the minerals predominantly determining total water hardness, namely calcium and magnesium, remained of interest for the WHO (2005, 2006).

Since 1979, several studies have reported on a possible association between water hardness, or minerals contributing to water hardness, and mortality related to ischemic heart disease (IHD) or stroke (Comstock et al. 1980; Ferrandiz et al. 2004; Marque et al. 2003; Morris et al. 1961; Rubenowitz et al. 2000; Yang et al. 2006). The hypothesized effect of total water hardness on IHD mortality has been ascribed to the higher intake of calcium and/or magnesium from tap water itself (Eisenberg 1992; Marx and Neutra 1997; Rylander 1996). Other explanations of the observed effect between water hardness and IHD mortality are the presence of more trace elements in hard water (e.g., selenium, lithium, silicon, zinc) (WHO 1979), more toxicants such as lead in soft, low-pH corrosive water (Pirkle et al. 1985), or the level of acidity or hydrogen carbonate concentration in tap water (Rylander 2008).

Most studies that reported an inverse association between drinking water hardness and IHD or stroke mortality were ecologic studies (Kousa et al. …

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