J Water Health. 2008 Dec;6(4):433-42. doi: 10.2166/wh.2008.054.

A systematic review of analytical observational studies investigating the association between cardiovascular disease and drinking water hardness.

Catling LA1, Abubakar I, Lake IR, Swift L, Hunter PR.

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Abstract

The aim of this study is to systematically review and critically assess analytical observational epidemiology studies investigating the association between levels of drinking water hardness and cardiovascular disease. We searched electronic databases and used standardised forms to extract data and assess study quality. Of 2,906 papers identified, 14 met the inclusion criteria (nine case control and five cohort studies). Of the nine case control studies, seven examined both drinking water magnesium and calcium and risk of death from cardiovascular disease. A pooled odds ratio showed a statistically significant inverse association between magnesium and cardiovascular mortality (OR 0.75 (95%CI 0.68, 0.82), p < 0.001). Only two studies reported a statistically significant effect for calcium. Substantial heterogeneity between studies made calculation of a summary estimate for drinking water calcium inappropriate. Of three cohort studies reviewed, two were of good quality. A weak suggestion that softwater was harmful in females and possibly associated with a slightly greater risk of sudden death was reported, but there was no association between water hardness and mortality from stroke or cardiovascular disease. This study found significant evidence of an inverse association between magnesium levels in drinking water and cardiovascular mortality following a meta-analysis of case control studies. Evidence for calcium remains unclear.

Copyright IWA Publishing 2008.

Eur J Cardiovasc Prev Rehabil. 2008 Apr;15(2):185-9. doi: 10.1097/HJR.0b013e3282f15fce.

Hard drinking water does not protect against cardiovascular disease: new evidence from the British Regional Heart Study.

Morris RW1, Walker M, Lennon LT, Shaper AG, Whincup PH.

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Abstract

It has been previously suggested that hard drinking water in general, and in particular high calcium and magnesium intake from drinking water, protect against cardiovascular disease.

Prospective study of men from 24 British towns, with widely differing levels of hardness in drinking water.

A total of 7,735 men aged 40-59 years were recruited during 1978-1980. Estimates of town-level water hardness were available and tap water samples, taken from 947 participants who also answered a questionnaire about water consumption, were used to calculate individual calcium and magnesium intakes. Men were followed for incident of major coronary heart disease (CHD) and stroke, and CHD mortality for 25 years.

Water hardness varied from 0.27 to 5.28 mmol/l in the 24 towns. A weak inverse association was found between water hardness and incidence of cardiovascular disease (CVD) [hazard ratio (HR), 0.96 per two-fold increase, 95% confidence interval (CI), 0.91-1.01, P=0.08 after adjustment for age and seven established coronary risk factors]. No association was observed with CHD incidence (adjusted HR, 0.99, 95% CI, 0.94-1.04, P=0.62) or mortality (adjusted HR, 0.96, 95% CI, 0.90-1.02, P=0.18). Individual magnesium intake showed a positive, rather than an inverse, association with CHD incidence (adjusted HR, 1.10 per two-fold increase, 95% CI, 1.01-1.20, P=0.045); individual calcium intake was unrelated to CHD or CVD end points.

This study suggests that neither high water hardness, nor high calcium or magnesium intake appreciably protect against CHD or CVD. Initiatives to add calcium and magnesium to desalinated water cannot be justified by these findings.