Report of the Safe Drinking Water Committee of the National
Academy of Sciences, 1977
Pages 440 through 447 of the Report of the Safe Drinking
Water Committee of the National Academy of Sciences, 1977,
"Drinking Water and Health," by the National Academy of Sciences,
1977. International Standard Book No. 0-309-02619-9. It is
available from:
Printing and Publishing Office
National Academy of Sciences
2101 Constitution Ave.
Washington. DC 20419
The EPA funded the study, which states that the rates of
cardiovascular death among populations drinking very soft water
may be "as much as 15-20% higher than among populations using
hard water", as indicated by "more than 50 studies in nine
countries".
"In the United States, cardiovascular
diseases account for more than one-half of the approximate 2
million deaths occurring each year... It is estimated that
optimal conditioning of drinking water could reduce this
cardiovascular disease mortality rate by as much as 15% in the
United States "
[page] 440 DRINKING WATER AND HEALTH
. . . and the problem has been the
subject of several comprehensive reviews. The Subcommittee on
Morbidity and Mortality, in preparing this report, has relied
heavily on several of these reviews, notably those by Craun and
McCabe (1975), Heyden (1976), Neri et al. (1974), Sauer
(1974), Sharrett and Feinleib (1975), Schroeder and Kraemer
(1974), and Winton and McCabe (1970). These reviews have been
abstracted and summarized rather than reprinting the same
material or attempting another review.
It should be noted, also, that the
World Health Organization and the International Atomic Energy
Agency consider that there is sufficient evidence for the
involvement of trace elements in the pathogenesis of
cardiovascular diseases to warrant international collaborative
studies on the problem (IAEA, 1973; WHO, 1973). The possible
causal association between water hardness and cardiovascular
disease has been recognized in Great Britain to be of enough
potential public health importance to have resulted in official
governmental expert review of the problem (MRC, 1970; COMA,
1974).
More than 50 studies in nine
countries have been carried out on possible relationship of water
hardness and health. Most of the investigations were in the
United Kingdom, United States, and Canada; they reveal a
consistent trend of significant statistical associations between
the hardness characteristics of drinking water and the incidence
of cardiovascular problems (heart disease, hypertension, and
stroke) and, to a lesser extent, other diseases. Generally,
reports have shown an inverse correlation between the incidence
of cardiovascular disease and the amount of hardness of drinking
water, or, conversely, a positive correlation with the degree of
softness. Studies in the United States and Canada have shown that
age-adjusted cardiovascular mortality rates among populations
using very soft water may be as much as 15-20% higher than among
populations using hard water. The differential reported for the
United Kingdom may be as high as 40%.
Cardiovascular diseases are the
leading cause of death in the United States, where they account
for more than 50% of all causes of death, or roughly 1 million
deaths each year, and death rates from coronary heart disease
have been steadily increasing over the past few decades.
It is evident, therefore, that if
water factors are ultimately proven to be involved causally in
the pathogenesis of cardiovascular disease, then we are
confronted with a major public health problem and current water
treatment practices will have to be greatly modified.
The credibility of these
water-factor studies depend more on the consistent trend of the
findings than their biological plausibility or the size of the
correlation coefficients or the actual significance levels.
Inorganic Solutes [page]
441
However, there is some scientific
justification for the biological plausibility of these
associations. There has been increasing evidence that certain
trace elements play an important role in a number of biological
processes through their action as activators or inhibitors of
enzymatic reactions, by competing with other elements and
proteins for binding sites, by influencing the permeability of
cell membranes, or through other mechanisms. It is assumed that
these elements can also directly or indirectly exert an action on
cardiac cells, the blood vessel walls, on blood pressure, or
other systems related to cardiovascular function, such as lipid
and carbohydrate metabolism. It is assumed further that water
quality can affect man's trace element or mineral balance and,
consequently, cardiovascular function.
As previously noted, the
preponderance of reported evidence indicates statistically
significant correlations between some drinking water factor(s)
and the incidence of cardiovascular diseases resulting in a
general impression that inorganic substances in water may be
causally implicated. It must be emphasized, however, that there
is considerable disagreement among various investigators
concerning the magnitude or even the existence of a "water
factor" risk, the identity of the water factor(s), the mode of
action, and the specific pathologic effects.
Theories on Risk Factors
Several hypotheses have been
offered on how components of drinking water may affect
cardiovascular function and disease; these generally fall into
one of the following classes:
1. That one or more of the principal "bulk" constituents of
hardness in tap water are protective.
2. That one or more of the trace elements that tend to be
present in hard water are protective.
3. That harmful metals are present in soft water, possibly
having been picked up by leaching from the distribution
system.
4. That other factors are involved. Each class of hypotheses
is briefly reviewed below.
PROTECTIVE EFFECT FROM BULK CONSTITUENTS OF HARD WATER
Hardness is not a specific constituent of water, but is a
complex and variable mixture of cations and anions. Several
investigators have attributed the disease-protective effect of
hard water to the presence of
[page] 442 DRINKING WATER AND HEALTH
calcium and magnesium, which are
the principal cations found in hard water. Calcium, magnesium,
and hardness generally correlate well with one another. In a few
studies, however, it was possible to discriminate between the two
elements and treat them as separate variables. When calcium and
magnesium are separately correlated with cardiovascular disease
rates, calcium appears to correlate with greater significance in
the United Kingdom, whereas in the United States the correlations
are about equally strong for calcium and magnesium.
There is a limited amount of
evidence to explain the possible mechanism whereby calcium and/or
magnesium may play a role in protection against cardiovascular
diseases. Experimentally, a moderate increase of calcium in the
diet results in lower levels of circulating and organ
cholesterol; this is speculated as a possible factor in the
association noted between water hardness and cardiovascular
diseases. Magnesium is theorized to protect against lipid
deposits in arteries and also may have some anticoagulant
properties that could protect against cardiovascular diseases by
inhibiting blood clot formation. Also, there is evidence to
indicate that there may be higher concentrations of calcium and
magnesium in certain tissues among residents of hard water areas
as compared to soft water areas.
PROTECTIVE ACTION OF TRACE ELEMENTS IN HARD WATER
There is a paucity of systematic
data concerning the concentrations of trace elements as a
correlate of hardness of water and cardiovascular disease rates.
From a limited number of studies that have been carried out, if
hard water contains protective beneficial elements (other than
calcium and magnesium), vanadium, lithium, and possibly manganese
and chromium emerge as candidates.
Lithium and vanadium have been
reported to be negatively correlated with cardiovascular
mortality. These negative correlations appear to persist and
remain significant even after controlling for calcium and
magnesium. The biological functions of these metals are obscure.
It is speculated that lithium may have a specific influence on
catecholamines and coronary-prone behavioral patterns. Vanadium
is reported as an essential trace element in human nutrition and
thought to inhibit hepatic cholesterol synthesis and reduce serum
cholesterol. Increased intake of vanadium is believed therefore
to reduce serum cholesterol. 'The mechanism is thought to be an
inhibition of cholesterol synthesis, especially in young
subjects.
A case is made that chromium, which is positively correlated
with the
Inorganic Solutes [page]
443
hardness of tap water in North
America (but not in the United Kingdom), may be causally
involved. Experimentally, chromium deficiency produces elevated
serum glucose and cholesterol levels and increased deposition of
aortic plaques. Though quantitative estimates of daily chromium
requirements cannot be given yet, it is thought that the chromium
level in hard water may help protect against a deficiency.
Similarly, it is speculated that hard water may protect against a
deficiency of manganese which also experimentally is associated
with decreased glucose tolerance.
HARMFUL ELEMENTS IN SOFT WATER
Soft water tends to be more corrosive than hard water. As a
result certain trace metals are found in higher concentrations in
soft than in hard water. Several such metals have been suggested
as possible intermediaries in the increased cardiovascular
disease rates associated with soft water. Based on very limited
data, cadmium, lead, copper, and zinc have been suspected to be
possibly involved in the induction of cardiovascular disease.
These metals often occur in plumbing materials and have been
found to leach into soft drinking water.
There is evidence that relatively low doses of cadmium can
produce hypertension in rats. It is known that the metal can
accumulate in human kidneys and produce renal damage and
presumably could affect blood pressure. However, direct evidence
linking cadmium in water to heart disease in humans is
lacking.
Several studies have shown elevated levels of blood lead
occurring among persons living in homes having lead plumbing and
soft water, or both. But the relationship between these elevated
blood lead levels and cardiovascular disease remains unclear.
There are limited data suggesting that the intake levels of
copper and zinc from soft water may adversely affect
cardiovascular disease rates. However, there are conflicting data
from other studies. Still other studies suggest that the
discrepancies may be due to the failure to examine critically the
ionic form and the intake ratios of the suspect metals from all
sources, particularly the Zn:Cu and the Cd:Zn ratios as well as
various other metabolic variables.
OTHER FACTORS AND CONFOUNDING VARIABLES
From the above discussion, it is apparent that there is no
shortage of hypotheses to explain how components of drinking
water might affect
[page] 444 DRINKING WATER
AND HEALTH
cardiovascular function and
disease. It is necessary to consider these hypotheses along with
other factors and some confounding variables.
Several cations found
predominantly in hard water are theorized to exert a beneficial
effect on cardiovascular function, and other cations found in
soft water, to exert a detrimental effect. The question often
raised is whether drinking water can provide enough of these
elements to have any significant impact on the pathogenesis of
cardiovascular diseases when considered in the context of the
total intake of these elements through other dietary and
environmental pathways. Hard or mineralized water generally would
supply less than 10-15% of the total dietary intake for calcium
and magnesium.
Water provides even a smaller
proportion of the total intake for the various suspect trace
metals with the possible exception of lead. The largest
proportion of trace metal intake from water compared to food is
for zinc, but even for this water provides only about 4% of its
total dietary intake. For all other suspect metals drinking water
provides under 4% of total intake. The concentrations of lead in
certain drinking waters may exceed 100 µg/liter as compared
to an average adult daily dietary intake of about 300
µg.
Several investigators, however,
point out that the amount of these elements provided through
drinking water relative to other sources is less important than
their chemical form. It is theorized that trace elements often
occur in a chelated form in foods and may be less available
metabolically than the ionized form that generally occurs in
water. Also, the valence form of elements found in water may
differ from that in foods and affect metabolic behavior.
Another possible variable is the
different effect of hard and soft waters on the mineral
composition of foods during cooking. It is theorized that soft
water may remove a significantly higher proportion of various
"protective" nutrients and elements from foods during cooking
than do hard waters.
Most of the studies carried out to
date correlate mortality rates with measurements made on raw
rather than on finished water; the correlations were of lesser
statistical significance when finished water was used.
There was considerable variation
in the study design and methods among the numerous investigations
reported. As previously noted, most of the studies report a
statistically significant correlation between water hardness and
one or more of several cardiovascular diseases. It is not
possible, however, to quantitatively compare the data from many
of these studies because of the different criteria and indices
used in the specification of cause of death. The case for a
causal association of water factors to any specific pathologic
effects is thought to be further
Inorganic Solutes [page]
445
weakened by several reports of
correlations of the water factor with other causes of death, such
as bronchitis, infant mortality, malignancies, cirrhosis, and
other noncardiovascular causes of death. Despite the consistent
trend for most of the reported studies, a few studies have shown
negative or conflicting results for different age and sex groups.
For example, in Holland and Sweden, hard water was correlated
with decreased cardiovascular mortality among women but not men,
and an opposite finding emerged from a study in Newfoundland.
The strength and specificity of
the correlative studies have varied depending on the sample sizes
of the area and population. In general, the relationship appears
stronger in larger and more populous areas.
To some extent these differences
are probably due to a lack of sensitivity of correlation
coefficients related statistically to the size of the sampling
unit. Obviously, smaller geographical units with smaller
populations would tend to have less stable death rates and
consistency than larger ones, so that any variable will tend to
correlate less well with smaller geographical and population
bases. But it should be noted that the size of the metropolitan
area and population density tend to correlate well with
cardiovascular disease rates independently of water quality. This
is attributed to various cultural and socioeconomic factors that
appear to influence cardiovascular disease mortality rates. On
the other hand, less urban areas are more likely to-use
relatively hard groundwater and, conversely, larger metropolitan
areas are usually more dependent on softer surface waters. In a
few studies where corrections for socioeconomic factors were
attempted, the correlations with hardness of water still exist
but with a reduced statistical significance. It is possibility
that both urbanization and water mineralization have an effect on
cardiovascular disease rates and could be interacting or acting
separately.
Several studies have shown
statistically significant correlations of death rates with
various geographical and climatic variables, especially rainfall,
independently of water-quality variables. Much more work must be
done on the possible associations and interrelationships of
variables such as rain, soil chemistry, and human nutrition with
water-quality and cardiovascular disease rates.
From this review, it is clear that
there is no shortage of hypotheses related to how the components
of drinking water might affect cardiovascular function and
disease. Despite the large body of evidence supporting the
hypotheses, there are too many confounding variables and
discrepancies in the data to permit any scientifically sound
conclusions as to the specific role of water factors in the
pathogenesis of cardiovascular diseases.
[page] 446 DRINKING WATER
AND HEALTH
Summary-Water Hardness and Health
There is a large body of
scientific information that indicates certain inorganic or
mineral constituents of drinking water are correlated with
increased morbidity and mortality rates. These constituents by
usual definition are not considered to be "contaminants," as they
often are associated with the level of "hardness" of drinking
water and occur naturally or are picked up from water-treatment
or distribution systems. Hardness is due primarily to the
presence of ions of calcium and magnesium and is expressed as the
equivalent quantity of calcium carbonate (CaCO3). Water with less
than 75 mg CaCO3/liter is generally considered soft, and above 75
mg/liter as hard.
A voluminous body of literature
suggests that in the United States and other developed nations,
the incidence of many chronic diseases, but particularly
cardiovascular diseases (heart disease, hypertension, and
stroke), is associated with various water characteristics related
to hardness. Most of these reports indicate an inverse
correlation between the incidence of cardiovascular disease and
the amount of hardness. A few reports also indicate a similar
inverse correlation between the hardness of-water and the causes
of risk from several noncardiovascular causes of death as
well.
Several hypotheses are reported on
how water factor(s) may effect health; these mostly involve
either a protective action attributed to some elements found in
hard water or harmful effects attributed to certain metals often
found in soft water.
The theorized protective agents
include calcium, magnesium, vanadium, lithium, chromium, and
manganese. The suspect harmful agents include the metals cadmium,
lead, copper, and zinc, all of which tend to be found in higher
concentrations in soft water as a result of the relative
corrosiveness of soft water.
It is evident from the review of
the literature that there is considerable disagreement concerning
the magnitude or even the existence of a "water factor" risk, the
identity of the specific causal factor(s), the mode of action,
and the specific pathologic effects.
Nevertheless, the preponderance of
reported evidence reflects a consistent trend of statistically
significant inverse correlations between the hardness of water
and the incidence of cardiovascular diseases. As a result, there
is a general impression that harmful elements in soft water
and/or protective elements in hard water are causally implicated
in the pathogenesis of cardiovascular and possibly other chronic
diseases.
The wide spectrum of alleged
associated effects, the lack of consistency in theorized or
reported etiologic factors, the very small quantities of
Inorganic Solutes [page]
447
suspect elements in water relative
to other sources, and the discrepancies between studies raise
serious questions as to whether drinking water really serves as a
vehicle of causal agents, is an indicator of something broader
within the environment, or represents some unexplained spurious
associations. Despite these uncertainties, the body of evidence
is sufficiently compelling to treat the "water story" as
plausible, particularly when the number of potentially
preventable deaths from cardiovascular diseases is considered.
In the United States,
cardiovascular diseases account for more than one-half of the
approximate 2 million deaths occurring each year. On the
assumption that water factor(s) are causally implicated, it is
estimated that optimal conditioning of drinking water could
reduce this annual cardiovascular disease mortality rate by as
much as 15% in the United States.
In view of this potential health
significance, it is essential to ascertain whether water factors
are causally linked to the induction of cardiovascular or other
diseases and, if so, to identify the specific factors that are
involved. Much more definitive information is needed in order to
identify what remedial water treatment actions, if any, can be
considered.
REFERENCES FOR TRACE METALS
Aberg, B., L. Ekman, R. Falk, U. Greitz, G. Persson, and J.0.
Snihs. 1969. Metabolism of methyl mercury (203 Hg) compounds in
man. Arch. Environ. Health 19:478-494.
Ackermann, W.C. 1971. Minor Elements in Illinois Surface
Waters. Illinois State Water Survey Technical Letter 14.
Adamson, A.H., DA. Valks, M.A. Appleton, and W.B. Shaw. 1969.
Copper toxicity in housed lambs. Vet. Rec. 85:368-369.
Aikawa, J.K., E.L. Rhoades, and G.S. Gordon. 1952. Urinary and
fecal excretion of orally administered Me. Proc. Soc. Exp. Biol.
Mod. 98:39-3 1.
Albert, R.E., R.E. Shore, A.J. Sayers, C. Strehlow, T.J.
Kneip, B.S. Pasternack, AJ. Friedhoff, F. Covan, and J.A. Cimino.
1974. Follow-up of children overexposed to lead. Environ. Health
Perspect., Exp. Issue no. 7, pp. 33-39.
Alberts, J.J., J.E. Schindler, and R.W. Miller. 1974. Mercury
determinations in natural waters by persulfate oxidation. Anal.
Chem. 46:434-437.
Aldous, K.M., D.G. Mitchell, and K.W. Jackson. 1975.
Simultaneous determination of seven trace metals in potable water
using a Vidicon atomic absorption spectrometer. Anal. Chem.
47:1034-1037.
Alexander, F.W., H.T. Delves, and B. E. Clayton. 1973. The
uptake and excretion by children of lead and other contaminants.
In Environmental Health Aspects of Lead, Proc. Int. Symp.,
Amsterdam, Oct. 2-6,1972. Luxembourg, Commission of the European
Communities, pp. 319-331.
American Public Health Association. 1976. Standard Methods for
the Examination of Water and Wastewater, 13th ed. Washington,
D.C.,
American Society for Testing and Materials. 1970. Annual Book
of ASTM Standards, pt. 23, Water and atmospheric analysis.
Philadelphia .
This page was first uploaded to The Magnesium Web Site on
December 10, 1998
http://www.mgwater.com/
Healthy Water
Association--USA