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American Journal of Epidemiology, Vol. 92, Vol 2, 1970




1 Seattle-King County Department of Public Health, Seattle, Wash. 98104, and Department of Preventive Medicine, University of Washington School of Medicine, Seattle, 98105.
2 Division of Biostatistics, Department of Preventive Medicine, University of Washington School of Medicine.
3 Department of Preventive Medicine, University of Washington School of Medicine.

  The Washington State Department of Health provided the death certificate data coded on punch cards suitable for computer processing as well as data on hardness of local water supplies and the population served by each. The Washington State Planning and Community Affairs Agency provided population estimates for counties as of April 1, 1965. The Washington/Alaska Regional Medical Program helped support computer processing of data. Dr. Anderson kindly supplied us with raw data from Ontario, Canada, to facilitate our comparative analysis.

(Received for publication February 20, 1970)

Peterson, D. R., D. J. Thompson and J. Nam (Univ. of Washington School of Medicine, Seattle, Wash.). Water hardness, arteriosclerotic heart disease and sudden death. Amer. J. Epid., 1970, 92: 90-93. —This study was undertaken to attempt to verify in the State of Washington the finding recently reported from Ontario, Canada, concerning the association of suddenness of dying from arteriosclerotic heart disease and water hardness. Though our methods differed somewhat, we could demonstrate from our data an inverse correlation similar to that found in Ontario suggesting we may have measured the same phenomenon. Verification by others using similar crude methods should be done before more rigorously designed studies can be considered warranted.

arteriosclerosis; coronary disease; death, sudden; heart diseases; water

Recently, T. W. Anderson et al. (1) reported that deaths which occur suddenly may be entirely responsible for the inverse relationship between mortality from arteriosclerotic heart disease and water hardness, noted in several previous studies (2-4). Death certificates signed by a coroner in the Province of Ontario, Canada, identified those who died suddenly. Death rates for coroner cases ascribed to arteriosclerotic heart disease, standardized for age and sex, revealed a downward trend from soft through intermediate to hard water categories. Non-coroner arteriosclerotic heart disease deaths did not show this trend. They speculated that some factor in soft water might influence the mechanism of death (proneness to cardiac arrhythmia, for example) when superimposed on arteriosclerotic heart disease. Intrigued by this concept, we attempted to duplicate their study, hoping to corroborate observations made in Ontario, Canada.


Because Washington State has a total population about one-half that of the Province of Ontario, we collected mortality data for two calendar years (1966 and 1967) to compare with the Ontario data for 1967. This procedure yielded approximately 64,000 Washington State certificates of death (all ages, all causes) compared with 55,000 for Ontario. We computed age, sex, and cause-specific rates for “Arteriosclerotic Heart Disease Including Coronary Artery Disease” (International Classification of Diseases, Adapted, Rubric 420) and for “All Other Natural Causes” (I.C.D.A. rubrics 001 through 795 excluding 420) as was done in Ontario. We compared the frequency of deaths during each of the two calendar years for each diagnostic category and for each age and sex group and found close agreement. Accordingly, we halved the calculated two year rates to achieve an average annual rate. To facilitate comparison with Ontario, we standardized the rates for sex and age using 10-year age groups within the age range 35-74 years and the population of Ontario as the referent population.

Data on hardness of local public water supplies and the population served by each, enabled us to calculate an index of average water hardness for 18 counties within Washington State as was done in Ontario. We excluded 21 counties with sparse populations and insufficient data with which to compute a water hardness index. With this exclusion, we found 22,935 Washington State deaths over the age range 35-74 years for analysis compared with 25,519 in Ontario. Counties with a hardness index of less than 100 parts per million (average 61.0 ppm) and those with 100-200 parts per million (average 134.2 ppm) corresponded to the classification used in Ontario. None of the 18 counties in Washington had an index exceeding 200 ppm hardness so comparisons with Ontario data in this category are precluded.

Washington State law specifies that the coroner in each county shall, among other duties, certify every death from natural causes if the deceased received no medical attention during the 36-hour period preceding death. We learned that the extent to which individual county authorities comply with this provision varies considerably. We surmized that a more consistent index of suddenness might be to categorize “sudden death”, alternatively, as those who were dead on arrival at hospital or who died at home, regardless of certification by the coroner. Using coroner’s cases yielded 4,199 certificates classifiable as “sudden” (19 per cent of all deaths). The alternative definition provided 6,239 “sudden” deaths (27 per cent compared with 26 per cent for Ontario). Individuals in the 55-74 year age bracket accounted for most of the difference between the alternative definitions of sudden death. Counties comprising the soft water category had proportionately fewer coroner certified deaths among older individuals than counties with harder water.


Age and sex adjusted death rates based on coroner certified certificates in Washington State differed from those in the Province of Ontario both in magnitude and trend in relation to water hardness category. Excluding deaths and populations in cities over 100,000 population did not alter these discordant findings.

The Washington State data trends became concordant with those from Ontario on classifying certificates for those who died at home or who were dead on arrival at hospital as “sudden”, regardless of certification by coroners (table 1). To further assess the comparability of this alternative definition of “sudden” with the classification used in Ontario, we computed the proportionate distribution in each category shown in the table. In Washington State 55 per cent of arteriosclerotic heart disease deaths were “sudden” in the “less than 100” water hardness category and 44 per cent were “sudden” in the 100-200 ppm water hardness category. The corresponding figures for Ontario were 47 per cent and 42 per cent. The same calculations for non-arteriosclerotic heart disease deaths classified as sudden yielded 18 per cent and 13 per cent for Washington State and 17 per cent and 17 per cent for Ontario.

Peterson Table 1

Adding sudden and not sudden arteriosclerotic heart disease rates reveals a dissimilarity in the soft water category with Ontario totalling 415 and Washington State 361. An explanation of this difference eludes us. In the harder water category, the corresponding rates total 390 and 402, respectively—rather close agreement. Overall, Ontario had 2,017 deaths per 100,000 population and Washington State 2,000.

Among the non-arteriosclerotic heart disease “sudden deaths” shown in the table, we ascertained that 25 per cent died from other forms of cardiovascular disease (stroke, hypertension, etc.) in areas served by soft water and 19 per cent in the harder water areas. This may explain why our data indicate a greater inverse water hardness relationship in this category than do the Ontario data.

We also ascertained the month of death for each of the diagnostic categories in each suddenness classification for each hardness area. We found no seasonal trends among sudden deaths different from non-sudden deaths in either water hardness category. Uniformly, slightly more deaths occurred during winter and spring than summer and fall.


Analysis of deaths certified by coroners in Washington State failed to corroborate the observations made in Ontario. We presume that Washington authorities may be prone to take less official notice of deaths involving older persons, perhaps simply because of the plethora of such events. Furthermore, older people probably consult physicians more frequently than younger ones, and thereby, would be more likely to have been medically attended prior to death and hence, not warrant coroner certification even though the deaths were sudden. We cannot explain why the soft and harder water categories differ in this respect, however.

The similarity of the rates and their trends in relation to water hardness that we acquired by using an alternate definition of “sudden death” suggests that we may have measured the same phenomenon originally reported from Ontario, despite our inability to exactly duplicate their methods.

The association we describe here should be verified by investigations in other areas before its credibility can be considered established. If analyses of crude data from several areas reveal consistent trends, more rigorously designed studies may be warranted.


1. Anderson, T. W., le Riche, W. H. and MacKay, J. S. Sudden death and ischemic heart disease. New Eng. J. Med., 1969, 280: 805-807.

2. Schroeder, H. A. Relation between mortality from cardiovascular diseases and treated water supplies; variations in states and 163 largest municipalities of the United States. J.A.M.A., 1960, 172: 1902-1908.

3. Morris, J. N., Crawford, M. D. and Heady, J. A. Hardness of local water supplies and mortality from cardiovascular disease in county boroughs of England and Wales. Lancet, 1961, 1: 860-862.

4. Crawford, M. D., Gardner, M. J. and Morris, J. N. Mortality and hardness of local water supplies. Lancet, 1968, 1: 827-831.

This page was first uploaded to The Magnesium Web Site on September 25, 2002