American Journal of Epidemiology, Vol. 92, Vol 2, 1970
ORIGINAL CONTRIBUTIONS
WATER HARDNESS, ARTERIOSCLEROTIC HEART DISEASE AND SUDDEN
DEATH
DONALD R. PETERSON1, DONOVAN J.
THOMPSON2 and JUN-MO NAM3
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.
METHODS
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.
RESULTS
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.
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.
CONCLUSION
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.
REFERENCES
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.
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