What is it?
is a mineral needed by every cell of your body. About half of
your body's magnesium stores are found inside cells of body tissues
and organs, and half are combined with calcium and phosphorus
in bone. Only 1 percent of the magnesium in your body is found
in blood. Your body works very hard to keep blood levels of magnesium
Magnesium is needed for more than 300 biochemical reactions in
the body. It helps maintain normal muscle and nerve function,
keeps heart rhythm steady, and bones strong. It is also involved
in energy metabolism and protein synthesis (2).
foods provide magnesium?
vegetables such as spinach provide magnesium because the center
of the chlorophyll molecule contains magnesium. Nuts, seeds, and
some whole grains are also good sources of magnesium (3).
Although magnesium is present in many foods, it usually occurs
in small amounts. As with most nutrients, daily needs for magnesium
cannot be met from a single food. Eating a wide variety of foods,
including five servings of fruits and vegetables daily and plenty
of whole grains, helps to ensure an adequate intake of magnesium.
content of refined foods is usually low (4). Whole-wheat bread,
for example, has twice as much magnesium as white bread because
the magnesium-rich germ and bran are removed when white flour
is processed. The table of food sources of
magnesium suggests many dietary sources of magnesium.
provide magnesium, but the amount varies according to the water
supply. "Hard" water contains more magnesium than "soft"
water. Dietary surveys do not estimate magnesium intake from water,
which may lead to underestimating total magnesium intake and its
is the Recommended Dietary Allowance for magnesium?
Recommended Dietary Allowance (RDA) is the average daily dietary
intake level that is sufficient to meet the nutrient requirements
of nearly all (97-98 percent) individuals in each life-stage and
gender group (4). The 1999 RDAs for magnesium for adults
(4), in milligrams (mg), are:
14 - 18
19 - 30
of two national surveys, the National Health and Nutrition Examination
Survey (NHANES III-1988-91) (5) and the Continuing Survey of Food
Intakes of Individuals (1994 CSFII) (4), indicated that the diets
of most adult men and women do not provide the recommended amounts
of magnesium. The surveys also suggested that adults age 70 and
over eat less magnesium than younger adults, and that non-Hispanic
black subjects consumed less magnesium than either non-Hispanic
white or Hispanic subjects (4).
can magnesium deficiency occur?
though dietary surveys suggest that many Americans do not consume
magnesium in recommended amounts, magnesium deficiency is rarely
seen in the United States in adults. When magnesium deficiency
does occur, it is usually due to excessive loss of magnesium in
urine, gastrointestinal system disorders that cause a loss of
magnesium or limit magnesium absorption, or a chronically low
intake of magnesium (4, 6-9).
with diuretics (water pills), some antibiotics, and some medicine
used to treat cancer, such as Cisplatin, can increase the loss
of magnesium in urine (4, 10). Poorly controlled diabetes increases
loss of magnesium in urine, causing a depletion of magnesium stores
(6). Alcohol also increases excretion of magnesium in urine, and
a high alcohol intake has been associated with magnesium deficiency
problems, such as malabsorption disorders, can cause magnesium
depletion by preventing the body from using the magnesium in food.
Chronic or excessive vomiting and diarrhea may also result in
magnesium depletion (1, 9).
of magnesium deficiency include
confusion, disorientation, loss of appetite, depression, muscle
contractions and cramps, tingling, numbness, abnormal heart rhythms,
coronary spasm, and seizures (1, 4, 9).
may need extra magnesium?
adults who eat a varied diet do not generally need to take a magnesium
supplement. Magnesium supplementation is usually indicated when
a specific health problem or condition causes an excessive loss
of magnesium or limits magnesium absorption (2, 6, 7, 11-16).
may be required by individuals with conditions that cause excessive
urinary loss of magnesium, chronic malabsorption, severe diarrhea
and steatorrhea, and chronic or severe vomiting.
thiazide diuretics, such as Lasix, Bumex, Edecrin, and Hydrochlorothiazide,
can increase loss of magnesium in urine (7). Medicines such as
Cisplatin (10), which is widely used to treat cancer, and the
antibiotics Gentamicin, Amphotericin, and Cyclosporin also cause
the kidneys to excrete (lose) more magnesium in urine (6). Doctors
routinely monitor magnesium levels of individuals who take these
medicines and prescribe magnesium supplements if indicated.
diabetes increases loss of magnesium in urine and may increase
an individual's need for magnesium. A medical doctor would determine
the need for extra magnesium in this situation. Routine supplementation
with magnesium is not indicated for individuals with well-controlled
diabetes (14, 15, 17, 18).
abuse alcohol are at high risk for magnesium deficiency because
alcohol increases urinary excretion of magnesium. Low blood levels
of magnesium occur in 30 percent to 60 percent of alcoholics,
and in nearly 90 percent of patients experiencing alcohol withdrawal
(12). In addition, alcoholics who substitute alcohol for food
will usually have lower magnesium intakes (11, 12). Medical doctors
routinely evaluate the need for extra magnesium in this population.
of magnesium through diarrhea and fat malabsorption usually occurs
after intestinal surgery or infection, but it can occur with chronic
malabsorptive problems such as Crohn's disease, gluten sensitive
enteropathy, and regional enteritis (13). Individuals with these
conditions may need extra magnesium. The most common symptom of
fat malabsorption, or steatorrhea, is passing greasy, offensive-smelling
vomiting should not cause an excessive loss of magnesium, but
conditions that cause frequent or severe vomiting may result in
a loss of magnesium large enough to require supplementation. In
these situations, your medical doctor would determine the need
for a magnesium supplement.
with chronically low blood levels of potassium and calcium may
have an underlying problem with magnesium deficiency. Adding magnesium
supplements to their diets may make potassium and calcium supplementation
more effective for them (2, 16). Doctors routinely evaluate magnesium
status when potassium and calcium levels are abnormal, and prescribe
a magnesium supplement when indicated.
is the best way to get extra magnesium?
will measure blood levels of magnesium whenever a magnesium deficiency
is suspected. When levels are mildly depleted, increasing dietary
intake of magnesium can help restore blood levels to normal. Eating
at least five servings of fruits and vegetables daily, and choosing
dark-green leafy vegetables often, as recommended by the Dietary
Guidelines for Americans, the Food Guide Pyramid, and the Five-a-Day
program, will help adults at-risk of having a magnesium deficiency
consume recommended amounts of magnesium. When blood levels of
magnesium are very low, an intravenous drip (IV drip) may be needed
to return levels to normal. Magnesium tablets also may be prescribed,
but some forms, in particular magnesium salts, can cause diarrhea
(19). Your medical doctor or qualified health-care provider can
recommend the best way to get extra magnesium when it is needed.
are some current issues and controversies about magnesium?
and blood pressure
suggests that magnesium may play an important role in regulating
blood pressure (4). Diets that provide plenty of fruits and vegetables,
which are good sources of potassium and magnesium, are consistently
associated with lower blood pressure (20-22). The DASH study (Dietary
Approaches to Stop Hypertension) suggested that high blood pressure
could be significantly lowered by a diet high in magnesium, potassium,
and calcium, and low in sodium and fat (23-26). In another study,
the effect of various nutritional factors on incidence of high
blood pressure was examined in over 30,000 U.S. male health professionals.
After four years of follow-up, it was found that a greater magnesium
intake was significantly associated with a lower risk of hypertension
(27). The evidence is strong enough that the Joint National Committee
on Prevention, Detection, Evaluation, and Treatment of High Blood
Pressure recommends maintaining an adequate magnesium intake as
a positive lifestyle modification for preventing and managing
high blood pressure (28-30).
and heart disease
deficiency can cause metabolic changes that may contribute to
heart attacks and strokes (31-33). There is also evidence that
low body stores of magnesium increase the risk of abnormal heart
rhythms (4), which may increase the risk of complications associated
with a heart attack. Population surveys have associated higher
blood levels of magnesium with lower risk of coronary heart disease
(34-36). In addition, dietary surveys have suggested that a higher
magnesium intake is associated with a lower risk of stroke (37).
Further studies are needed to understand the complex relationships
between dietary magnesium intake, indicators of magnesium status,
and heart disease.
deficiency may be a risk factor for postmenopausal osteoporosis
(4). This may be due to the fact that magnesium deficiency alters
calcium metabolism and the hormone that regulates calcium (13).
Several studies have suggested that magnesium supplementation
may improve bone mineral density (4), but researchers believe
that further investigation on the role of magnesium in bone metabolism
and osteoporosis is needed.
is important to carbohydrate metabolism. It may influence the
release and activity of insulin, the hormone that helps control
blood glucose levels (15). Elevated blood glucose levels increase
the loss of magnesium in the urine, which in turn lowers blood
levels of magnesium [(14). This explains why low blood levels
of magnesium (hypomagnesemia) are seen in poorly controlled type
1 and type 2 diabetes.
the American Diabetes Association issued a consensus statement
that concluded: "Adequate dietary magnesium intake can generally
be achieved by a nutritionally balanced meal plan as recommended
by the American Diabetes Association." It recommended that
"... only diabetic patients at high risk of hypomagnesemia
should have total serum (blood) magnesium assessed, and such levels
should be repleted (replaced) only if hypomagnesemia can be demonstrated"
is the health risk of too much magnesium?
magnesium does not pose a health risk, however very high doses
of magnesium supplements, which may be added to laxatives, can
promote adverse effects such as diarrhea. Magnesium toxicity is
more often associated with kidney failure, when the kidney loses
the ability to remove excess magnesium. Very large doses of laxatives
also have been associated with magnesium toxicity, even with normal
kidney function (38). The elderly are at risk of magnesium toxicity
because kidney function declines with age and they are more likely
to take magnesium-containing laxatives and antacids.
of excess magnesium can
be similar to magnesium deficiency and include mental status changes,
nausea, diarrhea, appetite loss, muscle weakness, difficulty breathing,
extremely low blood pressure, and irregular heartbeat (4, 39-41).
of Medicine of the National Academy of Sciences has established
a tolerable upper intake level (UL) for supplementary magnesium
for adolescents and adults at 350 mg daily. As intake increases
above the UL, the risk of adverse effects increases (4).
of Food Sources of Magnesium (3)
percent Bran, 2 Tbs
Florida, 1/2 med
germ, toasted, 1 oz
dry roasted, 1 oz
shredded wheat, 2
pumpkin, 1/2 oz
dry roasted, 1 oz
mixed, dry roasted, 1 oz
cooked, 1/2 c
flakes, 1/2 c
cooked w/ water, 1 c
baked w/ skin, 1 med
cooked, 1/2 c
dry roasted, 1 oz
butter, 2 Tbs.
bar, 1.45 oz
baked beans, 1/2 c
baked w/out skin, 1 med
California, 1/2 med
cooked, 1/2 c
raw, 1 medium
mixed species, raw, 3 oz (12
golden seedless, 1/2 c packed
powder, unsweetened, 1 Tbs
whole wheat, 1 slice
raw, 1 c
fruit, raw, 1 med
chopped, boiled, 1/2 c
= Daily Value. DVs are reference numbers based on the Recommended
Dietary Allowance (RDA). They were developed to help consumers
determine if a food contains very much of a specific nutrient.
The DV for magnesium is 400 milligrams (mg). The percent DV (%DV)
listed on the nutrition facts panel of food labels tells adults
what percentage of the DV is provided by one serving. Even foods
that provide lower percentages of the DV will contribute to a