The group was asked to examine several issues relating to the
consumption of drinking water that has undergone significant
treatment relevant to drinking water guidelines aimed at
protecting and enhancing public health:
Drinking water as a source of essential minerals With all of
these considerations in mind, the following nutrients commonly
found in drinking water at potentially significant levels and of
particular interest in this assessment are:
Potassium
The following text is excerpted from the WHO draft report.
The entire report is available on the WHO website,
http://www.who.int/water_sanitation_health/dwg/nutconsensus/en/
where it may be downloaded free of charge.
Water hardness and cardiovascular disease
Over 80 observational epidemiological studies have been
reported in the published literature since 1957 relating water
hardness and cardiovascular disease risks. Most, but not all, of
the studies found an inverse (protective) association between
cardiovascular disease mortality and increased water hardness
(measure by calcium carbonate or another hardness parameter
and/or the calcium and magnesium content of water). The
associations were as reported in countries throughout the world
by different investigators with different study designs. Both
population and individual based studies have observed benefits.
The most frequently reported benefit was a reduction in ischemic
heart disease mortality. In addition, there is supporting
evidence from experimental and clinical investigations
suggesting a plausible mechanism of action for calcium and
magnesium. The significance of the epidemiological findings is
that beneficial health effects can possibly be extended to large
population groups on a long-term basis by adjusting the water
quality.
The strongest epidemiological evidence for beneficial effects
was for drinking water magnesium concentrations and there was
also evidence but not as strong for drinking water calcium
concentrations. Magnesium and possibly calcium may be effective
in reducing blood pressure in hypertensive individuals. Studies
have shown magnesium exerts multiple cellular and molecular
effects on cardiac and vascular smooth muscle cells, which is a
plausible basis to explain its protective action. Treatment of
suspected myocardial infarction cases with intravenous magnesium
salts dramatically reduced mortality due to arrhythmia and
infarction thirty days post therapy. Other micronutrients and
trace elements have not been extensively considered in these
epidemiologic studies, but nutritional studies suggest that some
may have an indirect or direct beneficial role associated with
their presence in drinking water. On the other hand, a recently
published study in Finland, suggested that iron and copper in
drinking water might be associated with increased risks of heart
attack. More studies are needed to better understand the
possible risks and benefits of these essential and other trace
elements found in water.
Hard water is a reliable and stable4 source of calcium and
sometimes magnesium although the absolute and relative
concentrations will vary greatly by source. Consumption of
moderately hard water containing typical amounts of calcium and
magnesium may provide an important incremental percentage of
their dally intake. Inadequate total dietary intakes of calcium
and magnesium are common worldwide. Therefore, and incremental
contribution from drinking water can be an important supplement
to approach more ideal total daily intakes. Moreover, hard water
can reduce the losses of calcium, magnesium and other essential
minerals from food during cooking. If low mineralized water is
used for food and beverage production, reduced levels of Ca, Mg
and other essential elements would also occur in those products.
Low intakes would occur not only because of the lower
contribution of these minerals from water used in beverages, but
also because of the high losses of the minerals from food
products (e.g., vegetables, cereals, potatoes or meat) into
water during cooking.
The group concluded that there is sufficient epidemiological
evidence of an inverse relationship between calcium and
magnesium concentrations in drinking water and ischemic heart
disease mortality, and that consumption of water containing
calcium and magnesium, and therefore also the reintroduction of
Mg and Ca into demineralized water in the remineralization
process would likely provide health benefits in those consumer
populations. There are no known harmful human health effects
associated with the addition of calcium and magnesium within a
large range and the nutritional benefits are well known. In
addition, limited but suggestive evidence exists for benefits
associated with other diseases (stroke, renal stone formation,
cognitive impairment in e4lderly, very low birth weight, bone
fractures among children, pregnancy complications, hypertension,
and possibly some cancers). Adding calcium and magnesium to the
demineralized water would be a relatively inexpensive preventive
intervention that does not require individual behavioral change,
and it is already done as part of many water treatment
processes. The intervention could not only provide health
benefits but also help reduce medical care costs.
Epidemiological studies in the United Kingdom, United States,
Sweden, Russia and France, and research on changes in
calcium/phosphorus metabolism and bone decalcification provide
informatio9n about drinking water levels of calcium and
magnesium (and water hardness) that may provide beneficial
health effects. It has been suggested that reduced
cardiovascular mortality and other health benefits would be
associated with minimum levels of approximately 20 to 30 mg/l
calcium and 10 mg/l magnesium in drinking water. The percentage
of the recommended daily allowance (RDA) of calcium and
magnesium provided by drinking water at these minimum levels
will vary among and within countries. Thus, lower levels in
water may be sufficient to provide health benefits in some
areas, but higher levels may be beneficial in others. Some
limited information suggests that the desirable levels may be
higher in some circumstances. Overall health benefits will be
dependent upon total dietary intakes and other factors in
addition to water levels. Because the exposure-response
information is limited, further analyses, and possibly
additional studies are needed to determine the levels of calcium
and magnesium that may provide most favorable population
benefits in each location.
Recommendations
There is a need for more precise data on the impact of fluid
composition and intake, including water and other aqueous
beverages, on nutrient intake under a broader range of
physiologic and climatic conditions for sensitive population
segments in order to more precisely evaluate the importance of
minerals in drinking water on mineral nutrition.
Studies on the mineral nutritional content and adequacy of
world diets should be conducted so that adequacies and
inadequacies can be documented and mitigated.
National governments and water suppliers should be encouraged
to practice stabilization of demineralized water with additives
that will increase calcium and magnesium levels and to conduct
studies that monitor public health impacts.
Community and bottled water suppliers should provide
information to the general public and health professionals on
the composition of water for constituents including possibly
beneficial substances. Water bottlers should also consider
providing waters with mineral compositions that are beneficial
for population segments.
Additional studies should be conducted on potential health
consequences associated with consumption of both high and low
mineral content waters in addition to consideration of water
hardness. When studies are conducted, investigators should
consider exposures to both calcium, and magnesium levels in
addition to other minerals and trace elements that nmay be
present in hard and soft waters.
Unless properly stabilized, demineralized and some natural
waters are corrosive to plumbing resulting in damage to the
plumbing systems and also potentially increased exposure on
metals such as copper and lead. Information should be provided
on methods of application of home water softening devices so
that consumers will also have access to mineralized water for
drinking and cooking.
In the revisions of the GDWQ, WHO should consider the
beneficial roles of nutrient minerals and also water hardness
characteristics when it establishes numerical drinking water
guidelines for those substances. Chemicals used in the treatment
of drinking water should be assured to by of suitable quality
for that application so as not to contribute unacceptable amount
of potentially harmful chemicals to the finished water.
Additional epidemiologic studies of populations that consume
low mineral or demineralized water need to be conducted. Studies
should be focused on consumption of low mineral content or
distilled waters by population subgroups. Investigators may take
advantage of natural experiments (communities changing water
sources and treatment) to conduct population intervention
studies to evaluate potential health impacts. For example,
studies could compare communities before and after changing
source waters, or the introduction of treatment technologies
that significantly change water composition.
