American Journal of Medicine, Vol. 105 August. 1998, pages
125-130
Variation in the Mineral Content of Commercially Available
Bottled Waters: Implications for Health and Disease
Philippe Garzon BSca and Mark J. Eisenberg MD,
MPHb
a Department of Physiology, McGill University,
Montreal, Quebec, Canada (PG)
b Department of Medicine, Jewish General Hospital
(MJE), McGill University, Montreal, Quebec, Canada
PURPOSE: Although the annual consumption of
bottled water in North America is 12.7 gallons per capita,
little is known about the potential health effects of these
waters. We reviewed the amounts of major minerals found in
commercially available bottled waters, the recommended daily
allowances for these minerals, and their beneficial and harmful
effects.
METHODS: We obtained the mineral content of
various commercially available bottled waters in North America
and Europe from The Pocket Guide to Bottled Water. We then
conducted a Medline search to identify articles examining the
beneficial and harmful effects of magnesium, sodium, and
calcium.
RESULTS: Great variation exists in the
mineral content of commercially available bottled waters. Among
the bottled waters that we reviewed, the magnesium content
ranges from 0 to 126 mg per liter, the sodium content ranges
from 0 to 1,200 mg per liter, and the calcium content ranges
from 0 to 546 mg per liter. Epidemiologic and clinical studies
suggest that magnesium may reduce the frequency of sudden
death, that sodium contributes to the occurrence of
hypertension, and that calcium may help prevent
osteoporosis.
CONCLUSION: The ideal bottled water should
be rich in magnesium and calcium and have low sodium content.
Because there is great variation in the mineral content of
commercially available bottled waters, the actual mineral
content of bottled water should be considered when selecting
one for consumption. Am J Med. 1998;105:125-130. (c)1998 by,
Excerpta Medica, Inc.
Index Terms: fluid intake; sodium intake;
calcium intake; drinking water; mineral water; sodium;
magnesium; calcium
Over the past decade, the popularity of bottled water has
increased substantially in North America(1). Sales of bottled
waters have increased by 400%, and 1 in 5 households now use
bottled drinking water (2). Annual per capita consumption has
risen from less than 8 gallons in 1991 (1,2) to 12.7 gallons in
1997 (Arthur von Wiesenberger, personal communication). Since
bottled water is beginning to assume a prominent place in the
North American diet, its health effects require evaluation. In
this paper, we focus on the three most common minerals-magnesium,
sodium, and calcium- in commercially available bottled waters.
Many studies suggest that magnesium may protect against sudden
death (3-8), that sodium contributes to the occurrence of
hypertension (9 -18), and that calcium may help reduce the
incidence of osteoporosis (19,20). Because wide variations exist
in the mineral content of commercially available bottled waters,
understanding the potential beneficial and harmful effects of
these minerals will provide valuable information about which
bottled water to choose.
METHODS
We obtained the mineral content of various commercially
available bottled waters in North America and Europe from The
Pocket Guide to Bottled Water(21). This book describes the
mineral content of commercially available bottled waters, most of
which were verified via different Internet sites. We then
reviewed the English language medical literature for the years
1990 to 1996 to identify articles examining the health benefits
of the major minerals found in these waters, using the key terms
of magnesium, sodium, calcium, heart, and bottled water. We also
conducted an Internet search using the same key terms. Pertinent
articles identified in the Medline and Internet searches were
reviewed, and selected references from these articles were also
examined.
Variation in Mineral Content of Bottled Waters
Substantial variations in the concentrations of the three
major minerals were observed in the bottled waters studied.
Magnesium content ranges from ) to 126 mg perliter, sodium
content ranges from 0 to 1,200 mg per liter, and calcium content
ranges from 0 to 546 mg per liter. In general, waters bottled in
North America (Table 1) had low mineral contents, while waters
bottled in Europe (Table 2) had high mineral contents. For the
North American bottled waters, the median concentration for
magnesium was 2.5 mg per liter, for sodium it was 5 mg per liter,
and for calcium it was 8 mg per liter, For the European bottled
waters, the median concentration for magnesium was 23.5 mg per
liter, for sodium it was 20 mg per liter, and for calcium it was
115 mg per liter.
When comparing the mineral contents of bottled water, it is
important to know the variation of the mineral content from
bottle to bottle. According to the technical director of the
International Bottled Water Association, variation of mineral
content is less than 5% (Arthur von Wiesenberger, personal
communication) mainly due to different testing methods. We did
not find any published studies that looked at the mineral content
of tap water. However, from the limited information we were able
to obtain, it appears that tap water in major North American
cities contains relatively low levels of magnesium (<48 mg per
liter), sodium (< 195 mg per liter), and calcium(<85 mg per
liter).
Recommended Dietary Allowances
The Recommended Dietary Allowances (RDA) are estimates of the
required amount of nutrients needed for the average individual as
determined by a scientific committee selected by the National
Academy of Sciences and approved by the National Research Council
(22). The committee on Dietary Allowances has proposed a minimum
daily required intake for both magnesium (350 mg) and calcium
(800 mg). For sodium, a maximum intake of 2,400 mg has been
recommended.
Magnesium Physiology and Nutrition
Magnesium is the second most common intracellular cation,
after potassium (23). It is responsible for several biologic
processes that influence membrane and mitochondrial integrity,
such as the proper functioning of adenosine triphosphatase
(sodium-potassium ATPase)(3). In addition, magnesium is also
essential for the synthesis and stability of nuclear DNA and for
the mineralization of bone (24).
It is estimated that the body requires 220 to 410 mg of
magnesium daily (3). The average magnesium intake in the United
States ranges from 240 to 365 mg per day(23,25,26), but magnesium
intake in several regions of the United States is often
inadequate to meet daily requirements (26,27). Nuts, green leafy
vegetables, cereals, and seafood have a high magnesium content
(3). However, if these foods are boiled in soft water, they will
tend to release their magnesium, whereas boiling these foods in
hard water prevents loss of magnesium (26). Furthermore, due to
differences in absorption, magnesium bio-availability may be
greater from water than from food sources (3).
In some geographic areas, the magnesium content of drinking
water may provide 20% to 40% of a person's daily magnesium
requirement (28). For example, a liter of water with a magnesium
content of 100 mg per liter contains 29% of the daily magnesium
requirement of 350 mg per day (22). However, a liter of water
that is low in magnesium (eg, <1O mg per liter) provides less
than 3% of the daily requirement.
Magnesium Deficency and Sudden Death
Cardiovascular disease rates may be inversely related to water
hardness (3,5- 8). Rates of cardiovascular mortality and sudden
death are 10% to 30% greater in soft water areas (low in
magnesium or calcium) than in hard water areas (high in magnesium
or calcium) (3). Magnesium intake may have a cardioprotective
effect, perhaps correlated with a reduction in rates of sudden
death (29,30).
Animal and clinical studies also support an inverse
relationship between magnesium intake and sudden death, for which
two potential mechanisms have been proposed: arrhythmogenesis and
coronary artery vasospasm. According to the arrhythmogenesis
theory, magnesium deficiency promotes cardiac irritability,
perhaps by causing malfunction of sodium-potassium ATPase (31).
Clinical reports also suggest that magnesium deficiency lowers
the threshold for digitalis-toxic arrythmias, and that in certain
cases, intravenous magnesium can reverse cardiac rhythm
disturbances (3). A second theory proposes that magnesium
deficiency promotes coronary artery vasospasm, leading to
myocardial ischemia and sudden death. Several animal studies have
provided evidence supporting this theory (32-34). In these
studies, magnesium-deficient solutions induced vasospasm in
aortic strips from rats that resolved with the addition of
magnesium (32). Other studies have related magnesium deficiency
with pathologic changes in the heart that have been linked to
chronic myocardial ischemia (35,36).
Sodium Physiology and Nutrition
Sodium, the most abundant extracellular cation, maintains the
osmolarity of extracellular fluid and is the main determinant of
extracellular fluid volume (24). Acid-base balance and the
transmission of nerve impulses are other important functions
performed by sodium (37).
A great number of sodium-rich foods are found in the North
American diet, including cheese, bread, cereals, and processed
and preserved foods (22, 24). For example, 1 ounce of cocktail
peanuts contains 121 mg of sodium, a 3/4 cup serving of
cornflakes contains 211 mg of sodium, and a 1/2 cup serving of
instant chocolate pudding contains 440 mg of sodium (22). Because
the estimated minimum daily requirement of sodium for an adult
(500 mg per day) (22) is easily achieved in most North American
diets, no minimum recommended intake of sodium has been set by
the Food and Drug Administration. However, the National Research
Council has recommended limiting daily sodium intake to less than
2,400 mg (6 grams of salt), and the American Heart Associalion
recommends limiting sodium intake to 3,000 mg per day (22). In
contrast, the average sodium intake in North America has been
estimated to be 4,000 to 6,000 mg per day (22). Drinking 1 liter
of bottled water with a high sodium content (such as Vichy
Springs-1,095 mg of sodium per liter) may provide an individual
with 45% of the maximum recommended daily sodium intake. By
choosing a bottled water low in sodium, such as Poland Spring (4
mg sodium per liter), sodium intake can be minimized.
Sodium Intake and Hypertension
In North America, hypertension affects 20% of the entire
population (38). A persistent diastolic blood pressure increase
of 5 mm Hg is associated with a 34.% increase in the risk of
stroke and a 21 % increase in the risk of coronary heart disease
(39). High salt intake is believed to be an important contributor
to the occurrence of hypertension(38). Sodium is the major cation
found in most salts, and it is believed to be the ion responsible
for the hypertensive effects of a high salt intake.
For many non-Western societies, hypertension is rare and the
average blood pressure is low and does not increase with age
(15,40,41). For example, the Yanomamo Indians of northern Brazil
and southern Venezuela, who have low sodium diets, have blood
pressures averaging less than 110/70 mm Hg (42). Genetically
related populations with dissimilar diets were compared with
these groups, and the population with the higher sodium intake
had higher average blood pressures (16). In addition, when groups
of people with low sodium diets had increased sodium intake, an
increase in blood pressure was also observed (24). A highly
significant relationship has been observed between average blood
pressure and sodium intake in many populations around the world
(Figure 1) (43). However, studies in industrialized populations
have not found as close a relationship between sodium intake and
hypertension (24), perhaps due to the sigmoidal shape of the
curve linking salt intake and hypertension (Figure 2). Further
rises in blood pressure are relatively minor after a sodium
intake of 2,300 mg per day is achieved (44). The average daily
sodium intake in Western societies ranges from 2,300 to 7,000 mg,
making the relationship between salt intake and hypertension
barely evident (24).
Animal studies have also demonstrated that hypertension can be
induced or made more severe by increasing sodium intake, and that
hypertension can often be prevented by sodium restriction
(12,45-47). For example, experimental animals have been made
hypertensive by providing them with 1% and 2% saline solutions
for drinking water.
Since the seminal study of Kempner et al (48), many
investigators have looked at the effects of salt restriction on
blood pressure. Cutler et al (49) performed a meta-analysis of
these studies and concluded that a reduction of sodium intake to
1,500 to 1,700 mg per day would result in a decrease of 4 to 6 mm
Hg in systolic blood and of 2.3 mm Hg in diastolic blood
pressure.
Calcium Physiology and Nutrition
Calcium is the most abundant mineral in the body. The bone
contains 99% of the body's calcium, while the blood contains only
1% (24). Calcium helps regulate muscle contraction, helps
transmit nerve impulses, and regulates ion exchange across cell
membranes. It also helps in the secretion of hormones, digestive
enzymes, and neurotransmitters (22,24).
Naturally bioavailable calcium is found almost exclusively in
milk, milk products, and water. Because the intake of these
products is often low, many foods are now fortified with calcium
(eg, orange juice). Calcium can also be found in small amounts in
several vegetables, many of which contain binders that impede its
absorption (22). Among the few vegetables that contain
bioavailable calcium are mustard greens, parsley, broccoli, and
kale (22).
The recommended dietary allowance for calcium after 24 years
of age for both men and women is 800 mg per day (22); the need is
higher during childhood, fetal growth, pregnancy, and lactation.
However, nutritional surveys indicate that the calcium intake of
more than 50% of the North American population is well below the
National Research Council's daily recommendation (Figure 3)(22).
This imbalance is especially true for adult women, who have an
average consumption of 600 mg of calcium per day (22). Thus, the
average North American woman needs an extra 200 mg of calcium per
day.
The bioavailability of calcium in water is believed to be at
least as high as that of milk and milk products (50,51).
Therefore, selecting a bottled water with a high calcium content
may help achieve the daily recommended intake. For example, a
liter of Contrexeville bottled water contains 546 mg of calcium,
about 68% of the recommended daily allowance.
On the other hand, ingesting too much calcium may lead to the
formation of kidney stones. As a low calcium diet (400 to 600 mg
daily) has been suggested as a preventive treatment for patients
with type 2 idiopathic hypercalciuria(52), people with a history
of kidney stone formation might benefit from avoiding bottled
waters with a high calcium content.
Calcium Defiency and Osteoporosis
Over 24 million people in North America are at risk for
osteoporosis (53), which may be prevented by increasing peak bone
mass (22,24). A population-based studv observed a reduced rate of
age-related bone loss and hip fractures in a community receiving
a high calcium diet in comparison with an adjacent community on a
low calcium diet (54). In another study, an inverse relationship
between calcium intake and osteoporotic vertebral fracture
frequency was seen. For example, Finnish women, with the highest
daily calcium intakes (1,300 mg per day), had the lowest
frequency of fractures. In comparison, Japanese women, with the
lowest daily calcium intake(400 mg per day), had the greatest
frequency of fractures(20,54).
When animals are fed calcium deficient diets, their bones
become susceptible to fractures (54). A low calcium diet resulted
in a loss of trabecular bone in adult cats, a generalized
thinning of bone in dogs, and a decreased bone mass in young
growing rats (20). The bones of experimental animals become weak,
soft, and lack density when their diets lack calcium, phosphorus,
and vitamin D.
Other Minerals
Bottled waters contain other minerals as well as trace
elements that have important functions in the body. For example,
chromium may reduce fatty acids and cholesterol levels in the
blood, while copper may play a role in the formation of
hemoglobin. Zinc may help in the proper functioning of the immune
system, enzymes, taste, and smell; it may also help in the
healing process of body tissues. However, the content of trace
elements in most bottled waters is low and their dailv
requirements are usually met with normal dietary intake.
CONCLUSION
Consumption of bottled water in North America has been
increasing for the past 2 decades. In 1997, per capita
consumption was 12.7 gallons per year in the United States as a
whole (Arthur von Wiesenberger, personal communication) and over
20 gallons per year on the West Coast (1,2). A wide variation
exists in the mineral content of bottled waters that are
commercially available in North America and Europe: magnesium
content ranges from 0 to 126 mg per liter, sodium from 0 to 1,200
mg per liter, and calcium from 0 to 546 mg per liter. Evidence
links magnesium deficiency to sudden death, excess sodium to
hypertension, and calcium deficiency to osteoporosis. Drinking
water that is high in magnesium and calcium and low in sodium
will help individuals achieve the recommended daily allowances of
these minerals. Because wide variations exist in the mineral
contents of commercially available bottled waters, understanding
the potential beneficial and harmful effects of these minerals
will provide valuable information on which water to
choose.
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