Groundwater hardness may explain geographical differences in the incidences of heart disease
Photo: Marika Sinervo/vastavalo.fi
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Could geographical differences in the incidences of
heart disease in Finland be at least partly explained
by differences in the hardness of groundwater and,
in particular, by the water’s magnesium content? This
argument has been put forward by Anne Kousa, PhD,
research scientist at the Geological Survey of Finland, who
defended her doctoral thesis on the subject in November.
Kousa’s research results indicate that the
hardness of well water and locally high
concentrations of magnesium are associated
with a lower incidence of acute
myocardial infarction. A high ratio of
magnesium to calcium in well water, on
the other hand, is associated with a higher
incidence of myocardial infarction. The
hardness of water is defined as the sum of
calcium and magnesium it contains.
It has been known for more than
60 years in Finland that the risk of heart
disease in different parts of the country varies, and that the risk is the highest in
Eastern Finland. Interestingly enough,
geographical variation in the incidences
and mortality rates for heart disease between
different countries and, within
countries, is also well established.
Research shows that the major coronary
heart disease risk factors, such as hypertension,
smoking and high cholesterol
levels, only explain about 40 per cent of
the geographical variation in the incidences
of heart disease within Finland.
Socio-economic and hereditary factors
may also partly explain the variation.
Heart disease mortality in Finland
has come down remarkably in recent
decades. Despite this, geographical differences
have remained almost unchanged
– some risk factors seem to cluster in
Eastern Finland. Men throughout Finland
have a significantly higher risk of
contracting heart disease compared to
women.
– It was more than 50 years ago when
the thought was first put forward that the
chemical properties of drinking water
may be associated with geographical variation
in heart disease. Many international
studies have been carried out on the subject,
but their results have been ambiguous.
Water hardness and water chemistry
have also been studied in Finland before, when trying to identify any environmental
factors explaining the regional differences
in the incidences of heart disease,
Anne Kousa notes.
Magnesium is known to have beneficial
effects on cardiac health. In rural
areas, its concentration in well water varies
between different areas.
Research based on
extensive databases
In her research, Kousa studies the geographical
association of local groundwater
hardness and the concentrations of
certain groundwater components with
incidences of acute myocardial infarction.
Study subjects were rural men and
women aged 35 - 74 years who had suffered
acute myocardial infarction. The data
for men was from the years 1983, 1988
and 1993, and the data for both men and
women was from the period 1991 - 2003.
Eighty per cent of Finns use drinking
water treated at waterworks but, in rural
areas, groundwater extracted from wells
is mostly used.
”The study was
based on extensive,
existing registers.”
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The study was based on extensive,
existing registers.
Geochemical data was obtained
from the groundwater database of the
Geological Survey of Finland. Population
and case data was obtained from the
Causes of Death register, the Finnish Hospital
Discharge Register and the Finnish
Cardiovascular Disease Register, as well
as from Statistics Finland. Geographical
information systems (GIS) are an important
tool in geomedicine. They are used
for studying the association between
geological factors and human health and
the geographical distribution of healthrelated
phenomena.
What was new about the data processing
method was that the definition of the
geographical research areas was not based
on administrative borders, such as local
authority or provincial borders. Instead,
the whole of Finland (excluding Lapland
and the Ålands) was divided into 10x10
km grids. The statistical analysis of grid
data was based on the address of each person
who had suffered myocardial infarction
at the time of diagnosis.
The results showed a geographical association
between the incidences of acute
cardiac infarction and the soft, well water
low in magnesium found in Eastern Finland.
Incidences in western and southern
Finland, where groundwater is hard and
contains magnesium and calcium, were
lower.
Kousa also studied the association of
zinc, aluminium, copper, fluoride, iron
and nitrate concentrations found in samples
of well water with the risk of heart
disease. These elements were not found
to have a geographical association with
the incidences of acute myocardial infarction.
TEXT Harriet Öster
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