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J Irish Med Assoc 55:17-18 (July) 1964

The Influence of Water Hardness and Rainfall on the Incidence of Cardiovascular and Cerebrovascular Mortality in Ireland

Risteárd Mulcahy, M.D., M.R.C.P.(Lond.),

Cardiac Department and Dept. of Preventive Medicine, St. Vincent’s Hospital, Dublin, 2.

SCHROEDER (1960a & 1960b) showed that there was a significant negative correlation between hardness of water and death rates from coronary heart disease and hypertensive heart disease in 163 urban areas in the United States of America. There was a less significant negative correlation with cerebrovascular disease and generalised arteriosclerosis. In other words, hardness of water seemed to have a protective action against these conditions. This type of epidemiological study was originally done by Kobayashi (1957) of Japan who showed variations in death rates from specific causes in different areas which correlated with certain geological features.

Morris, Crawford and Heady (1961) show negative correlations between water hardness and (1) total cardiovascular mortality, (2) deaths caused by vascular lesions of the central nervous system, (3) deaths certified as "myocardial degeneration", and (4) deaths in middle aged men caused by coronary heart.disease. There appears to be a significantly higher death rate under these four classifications in the soft water areas of England and Wales.

The hardness of water of the 15 largest urban areas in the Republic of Ireland was determined. These figures are shown in Table I with population figures for these 15 areas. Figures for annual average rainfall were also included in view of the statement by Morris et al. (1962) that rainfall, softness of water and cardiovascular mortality are highly associated. Generally the greater the rainfall the softer the water supply. The death rates for the period 1957-1961 inclusive for the following causes were also obtained for these areas:

(1) arteriosclerotic heart disease (IDL 420).

(2) arteriosclerotic heart disease and "myocardial degeneration" (IDL 420 and 422).

(3) total cardiovascular mortality (IDL 400-443).

(4) cerebrovascular mortality (IDL 331, 332, 334).

Irish Table I

Table II shows the correlation of (1) hardness of water, and (2) average annual rainfall with the death rates for the above causes in all age groups and in the age group 35-64.

Table II


None of these correlations approaches the level at which they can be considered as differing significantly from zero. The number of pairs of values, in each case, is only 15 and for so few observations the estimated coefficients of correlation would need to be outside the range of -0.514 to +0.514 to indicate a significant deviation at the 5% level.

It is clear from these results that local geological and climatic conditions do not appear to play an important part in determining the incidence of cardiovascular disease in the Republic of Ireland. This conclusion contradicts the findings reported from Japan, the United States, and England and Wales.

As in other countries there arc substantial variations in the certified incidence of death from various causes in the different cities and towns of Ireland. Table III illustrates this variation in the average annual death rate (1957-1961) for arteriosclerotic heart disease and "myocardial degeneration" (IDE 420 and 422) in the 15 largest urban areas. Unlike the findings in England and Wales, water hardness and rainfall do not appear to play part in determining these wide variations.

Table III


The total hardness of water, average annual rainfall and death rates from cardiovascular and cerebrovascular disease have been determined for the 15 largest urban areas in the Republic of Ireland.

Hardness of water and rainfall appear to play no part in determining the incidence of death from these causes.

These conclusions contradict the recent findings reported from Japan, the United States of America and Great Britain.


I am grateful to the Director of the Central Statistics Office, Dr. Donal McCarthy, and to his staff for supplying most of the information required for this study and for the analysis of the results. I am also grateful to the Secretary of the Department of Transport and Power for information on average annual rainfall. I wish to thank the engineers in charge of the Waterworks Departments of Dublin Corporation and Drogheda Corporation for their assistance.


Kobayashi, J. (1957). Ber. Ohara Inst., 11, 12.

Morris, J. N., Crawford, M. D. and Heady, J. A. (1961). Lancet, 1, 860.

Morris, J. N., Crawford, M. D. and Heady, J. A. (1962), Lancet, 2, 506.

Schroeder, H. A. (1960a) J. Amer. med. Assn., 172, 1902.

Schroeder, H, A. (1960b) J. chron, Dis., 12, 586.

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