Magnesium, Stress and the Cardiovascular System
Magnesium 5: 150-153 (1986)
Content of Magnesium in Drinking Water and Deaths from
Ischaemic Heart Disease in White South Africans1
W.P. Leary2
Department of Clinical and Experimental Pharmacology,
University of Natal Medical School, Durban, South Africa
1 Presented in part at the Fourth International
Symposium on Magnesium, Blacksburg, Va., July 23-28, 1985.
2The author's work was supported by the Medical
Research Council of South Africa.
Key Words. Water · Ischaemic heart
disease · White South Africans
Abstract. Mortality rates for acute
myocardial infarction and ischaemic heart disease (IHD) of
white males and females in South Africa are much higher than
those in the USA, Australia, England and Wales when individuals
in the 15- to 64-year age group are considered. Magnesium
levels in the drinking water of 12 South African districts and
deaths due to IHD assessed on the basis of corrected statistics
for deaths apparently due to IHD in white residents were
studied and a significant negative correlation was found
between these two variables. No such correlation has been
demonstrated in blacks.
Introduction
Ischaemic heart disease (IHD) accounts for the deaths of more
white South Africans than cancer and road accidents combined.
Within South Africa, IHD mortality rates for whites are higher
than those for blacks and are also higher than rates in America,
England and Wales and West Germany when individuals aged 15-64
are considered [3, 14].
No doubt, some South African deaths ascribed to IHD by medical
practitioners completing death certificates are due to acute
cardiac arrhythmias unrelated to IHD or, in some cases, to
catastrophic cerebrovascular accidents, but diagnostic errors of
this kind occur in most countries, particularly in rural areas,
where autopsies are seldom performed, and are unlikely to account
for any major bias in analyses of IHD rates.
Whereas it is generally accepted that risk factors such as
smoking, high serum cholesterol levels and hypertension are of
primary importance in the pathogenesis of IHD, data from various
sources suggest that the incidences of death from IHD and acute
cardiac arrhythmias may be influenced by regional differences in
dietary magnesium content [4, 8, 10]. This view is supported by
clinical and phiysio1ogica1 evidence that serious disorders of
cardiac rhythm may occur in magnesium deficiency of any origin
[7, 12].
When domestic water is supplied from natural sources, its
magnesium content approximates 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 acceptable indication of total average magnesium intake in any
given area [4, 8, 10] Utilizing this principle official data have
been examined 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 [5,
6].
Methods
The average magnesium content of drinking water in various
districts has been determined by the South African Department of
Environmental Affairs [6]. Data were based on a sampling
procedure whereby water from regional dams and rivers supplying
them was repeatedly examined by atomic absorption
spectrophotometry.
Analysis of these data allowed identification of localities
where the magnesium content of water varied from 0.04 to 1.85
mmol/l (1-45 mg/l) covering a wide range of possible magnesium
intakes Twelve districts were chosen on the basis of high or low
magnesium contents in drinking water prior to the acquisition of
any data on regional death rates from IHD.
Corrected statistics 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 [2, 5].
Spearman's (nonparametric) correlation coefficient (rho) was
calculated to determine whether any correlation existed between
deaths attributed to IHD and magnesium content in drinking
water.
Results
The results of this analysis have been published elsewhere [9]
and indicated a significant negative correlation between the
incidence of death apparently due to IHD and the magnesium
content of drinking water (rho = 0.68; p <0.02).
Discussion
The incidence of magnesium deficiency in South Africa is
unknown, although the low magnesium content of drinking water in
many areas and the popularity of alcoholic beverages and use of
laxatives and diuretics, which deplete the body of possibly
limited magnesium resources, suggest quite clearly that
deficiency is not uncommon. Certainly, careful studies carried
out in parts of Finland, in which water supplies are relatively
magnesium-deficient and sudden death, apparently from cardiac
causes, is common [8], suggest that magnesium deficiency is a
major cardiovascular risk factor. Furthermore, the view that
magnesium deficiency could be of pathogenic importance in
precipitating deaths from IHD is supported by experimental [13]
and epidemiological findings [4, 8, 10]. The mechanisms involved
are not clear although frank magnesium deficiency is associated
with changes in glucose tolerance, arterial resistance and the
high-density/low-density lipoprotein ratio [11] which aggravate
the risk of IHD.
The death rates for IHD used in the South African study were
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 [12], this bias is probably of
minor importance. It is possible that a small percentage of the
sudden deaths attributed to IHD were caused by acute
cerebrovascular events. It is unlikely that such misdiagnoses
occurred with greater frequency in low- or high-magnesium-level
areas, but it should be noted that experimental evidence has been
published, indicating that magnesium depletion causes spasm of
cerebral arteries [1] and may thus contribute to the pathogenesis
of cerebrovascular accidents.
In considering these preliminary findings, it would be as well
to note that IHD is relatively rare amongst black South Africans
who do, however, commonly suffer from stroke, hypertension and
cardiomyopathy. Since interracial differences in magnesium intake
are likely to be small, variables other than magnesium intake and
output must clearly be investigated in both population groups
with the objective of explaining the different incidences of IHD
observed in blacks and whites. Factors such as sodium, potassium,
calcium, alcohol and dietary unsaturated fat intakes all deserve
attention; clearly the problem is both interesting and
challenging and deserves extensive epidemiologically based
research.
La teneur en Mg de l'eau de boisson et les
décès par suite d'affections cardiaques
ischémiques chez des Sud-Africains de race blanche.
Les taux de mortalité par suite d'infarctus aigu du
myocarde et de maladie cardiaque ischémique d'hommes et de
femmes de race blanche en Afrique du Sud sont beaucoup plus
élevés que ceux observés aux Etats-Unis, en
Australie, en Angleterre et au Pays de Galles quand on prend en
considération le groupe d'âge de 15 à 64 ans.
Les taux de magnésium dans l'eau de boisson de 12
districts d'Afrique de Sud et les décès par suite
d'affections cardiaques ischémiques, étudiés
a l'aide de statistiques corrigées de décès
d'habitants blancs, ont été analysés et une
corrélation négative significative a pu être
établie entre ces deux variables. Une telle
corrélation n'a pas été mise en
évidence chez les noirs.
References
1 Altura, B.T.; Altura, B.M.: Withdrawal of magnesium causes
vasospasm while elevated magnesium produces relaxation of tone in
cerebral arteries. Neurosci. Lett. 20: 323-327
(1980).
2 Bradford Hill, A.: A short textbook of medical statistics,
p. 183 (Hodder & Stoughton, London 1977).
3 Brink, A.J.: Mortality rates due to ischaemic heart disease
in White South Africans. S. Afr. med. J. 65: 365
(1984).
4 Chipperfield, B.; Chipperfield, J.R.: Differences in metal
content of the heart muscle in death from ischemic heart disease.
Am. Heart J. 95: 732-737 (1978).
5 Department of Statistics RSA: Data on file.
6 Department of Environmental Affairs of RSA: Data on
file.
7 Flink, E.B.: Magnesium deficiency: aetiology and clinical
spectrum. Acta med. scand., suppl. 647 pp. 125-137 (1981).
8 Karpannen, H.: Epidemiological studies on the relationship
between magnesium intake and cardiovascular diseases. Artery
9: 190-199 (1981).
9 Leary, W:P.; Reyes, A.J.; Lockett, C.J.; Arbuckle D.D.; van
der Byl, K.: Magnesium and deaths ascribed to ischaemic heart
disease in South Africa. S. Afr. med. J. 64: 775-776
(1983).
10 Marier, J.R.: Nutritional and myocardial aspects of
magnesium in drinking water. Magnesium-Bull. 3: 48-54
(1981).
11 Reyes, A.J.; Leary, W.P.: Diuretic therapy, magnesium
deficiency and lipid metabolism. S. Afr. med. J. 64:
355-356 (1983).
12 Reyes, A.J.; Leary, W.P.. Pathogenesis of arrhythmogenic
changes due to magnesium depletion. S. Afr. med. J. 64:
311-312 (1983).
13 Turlapaty, P.D.M.V.; Altura, B.M.: Magnesium deficiency
provokes spasm of coronary arteries: relationship to etiology of
sudden death ischemic heart disease. Science 208:
198-200 (1980).
14 Wyndham, Cl-I.: The loss from premature death of
economically active manpower in the various populations of the
RSA. I. Leading causes of death. health strategies for reducing
mortality. S. Afr. med. J. 60: 411-419 (1981).
Received: August 19, 1985
Accepted: October 31, 1985
W.P. Leary,
Department of Clinical and Experimental
Pharmacology,
University of Natal Medical School,
Durban 4001 (South Africa)
This page was first uploaded to The Magnesium Web Site on
August 30, 2002
http://www.mgwater.com/
Healthy Water
Association--USA