Magnesium and deaths ascribed to ischaemic heart disease in
South Africa
A preliminary report
W. P. LEARY, A. J. REYES, C. J. LOCKETT, D. D. ARBUCKLE, K.
VAN DER BYL
Departments of Experimental and Clinical Pharmacology and
Community Health, University of Natal, Durban
Summary
The incidence of death from ischaemic heart disease (IHD) and
acute cardiac arrhythmias is increased in some regions where
magnesium levels are reduced in soil and water.
Magnesium levels in the drinking water of twelve South African
magisterial districts have been evaluated, together with
corrected statistics for deaths apparently due to IHD in White
males from the same districts. A significant negative correlation
was found between the incidence of deaths ascribed to IHD and the
magnesium content of drinking water. Future, prospective,
multivariate studies are required to elucidate whether magnesium
scarcity in a geological environment is a major coronary risk
factor.
S Afr Med J 1983; 64, 775-776
In South Africa statistics based on the examination of death
certificates indicate that there is a high death rate from
ischaemic heart disease (IHD) among Whites, Indians and Coloureds
(1), although a significant number of deaths ascribed to IHD by
practitioners who sign death certificates are certainly due to
acute cardiac arrhythmias unrelated to IHD or, in some cases, to
catastrophic cerebral haemorrhage. Diagnostic errors of this kind
are commonly made in all countries, particularly in rural areas
where pathology services are often limited.
Data from various sources suggest that the incidences of death
from IHD and acute cardiac arrhythmias may be influenced
unfavourably by regional deficiencies in dietary magnesium
content (2-4). This view is supported by clinical and
pathophysiological evidence that serious cardiac arrhythmias
occur in magnesium deficiency of any origin (5,6).
Magnesium concentrations in soil, water and locally grown
fruit and vegetables vary in accordance with regional geological
characteristic When domestic water is supplied from natural
sources its magnesium content is similar to that of the local
soil and farm produce and, in the absence of significant
supplementation from other sources, the level of magnesium in
drinking water provides an accepted indication of magnesium
intake in any given area . Utilizing this principle a preliminary
examination of official data (8,9) has been carried out to
determine whether any apparent relationship exists between deaths
ascribed to IHD and magnesium levels in the drinking water of
several selected South African towns.
Methods
Data on the average magnesium content of drinking water in
various districts during 1982 were provided by the Department of
Environmental Affairs, Pretoria (9). These data were based on a
sampling procedure whereby water from regional dams and rivers
supplying them was repeatedly examined by atomic absorption
spectrophotometry.
A preliminary survey of the data allowed identification of a
set of localities where the magnesium content of water varied
from 0,04 to 1,85 mmol/l (1-45 mg/l), allowing a wide range of
possible magnesium intakes. The districts studied were those of
Bloemfontein, Bothaville, Duiwelskloof, Durban, Hennenman,
Mafeking, Pietersburg, Potgietersrust, Postmasburg, Venterstad,
Virginia and Welkom. This selection preceded the acquisition of
any data on regional death rates from IHD.
Corrected statistics (10) for deaths in White males,
apparently due to IHD and derived from death certificates issued
during 1978, were supplied by the Department of Statistics,
Pretoria (8). Spearman's (non-parametric) correlation coefficient
(rho) was calculated to determine whether any correlation existed
between deaths attributed to IHD and magnesium content in
drinking water. The test was two-tailed and P = 0,05 was
considered the limit of significance.
Results
A significant negative correlation was found between the
incidence of death apparently due to IHD and the magnesium
content of drinking water (Fig. 1).
Discussion
The view that magnesium deficiency may be of pathogenic
importance in precipitating deaths from ischaemic heart disease
is currently supported by experimental (11) and epidemiological
findings (2-4). It may also be postulated that magnesium
deficiency is an aetiological factor in IHD since it decreases
glucose tolerance (12) and decreases the high-density/low-density
lipoprotein ratio.
The death rates for IHD used in the present study are
undoubtedly biased by the inclusion of patients who did not
suffer from IHD but died as a result of unrelated acute cardiac
arrhythmias. However, since magnesium deficiency is a proven
determinant of cardiac arrhythmias (6) this bias is of minor
importance.
It is possible that a small percentage of sudden deaths
attributed to IHD were caused by acute cerebrovascular events. In
this regard it is noteworthy that experimental evidence has been
published indicating that magnesium depletion causes spasm of the
cerebral arteries (14).
Future prospective multivariate studies are required in which
somatic magnesium status is related to the prevalence of IHD and
occurrence of deaths due to acute myocardial infarction,
independent arrhythmias and cerebrovascular accidents. The
incidence of all other known risk factors for IHD should also be
evaluated. Such studies should be multicentric and be carried out
by specially trained medical practitioners in small
environmentally and biologically homogeneous communities where
patients can be followed up.
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