Magnesium Information
Magnesium: What is it?
What foods provide magnesium?
What is the Recommended Dietary
Allowance for magnesium for adults?
When can magnesium deficiency occur?
Signs of magnesium deficiency
Who may need extra magnesium?
What is the best way to get extra magnesium?
What are some current issues and controversies about magnesium?
Magnesium and blood pressure
Magnesium and heart disease
Magnesium and osteoporosis
Magnesium and diabetes
What is the health risk of too
much magnesium?
Signs of excess magnesium
Table of Food Sources of Magnesium
Magnesium: What is it?
Magnesium 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 constant
(1).
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).
What
foods provide magnesium?
Green 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.
The 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.
Water can 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 variability (4).
What is the Recommended Dietary
Allowance for magnesium?
The 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:
| Life-Stage |
Men |
Women |
Pregnancy |
Lactation |
| Ages 14
- 18 |
410 mg |
360
mg |
400 mg |
360
mg |
| Ages 19
- 30 |
400 mg |
310
mg |
350 mg
|
310
mg |
| Ages 31
+ |
420 mg |
320
mg |
360 mg |
320
mg |
| Results 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). |
When can magnesium deficiency
occur?
Even 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).
Treatment 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 (11, 12).
Gastrointestinal 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).
Signs 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).
Who may need extra magnesium?
Healthy 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).
Extra magnesium 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.
Loop and 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.
Poorly controlled 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).
People who 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.
The loss 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 stools.
Occasional 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.
Individuals 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.
What is the best way to get extra magnesium?
Doctors 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.
What are some current
issues and controversies about magnesium?
Magnesium and blood pressure
Evidence 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).
Magnesium and heart disease
Magnesium 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.
Magnesium and osteoporosis
Magnesium 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.
Magnesium and diabetes
Magnesium 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.
In 1992, 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" (18).
What is the health risk
of too much magnesium?
Dietary 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.
Signs 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).
The Institute 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).
Table of Food
Sources of Magnesium (3)
| Food |
Milligrams
|
%DV*
|
| 100
percent Bran, 2 Tbs |
44
|
11
|
| Avocado,
Florida, 1/2 med |
103
|
26
|
| Wheat
germ, toasted, 1 oz |
90
|
22
|
| Almonds,
dry roasted, 1 oz |
86
|
21
|
| Cereal,
shredded wheat, 2
rectangular biscuits |
80
|
20
|
| Seeds,
pumpkin, 1/2 oz |
75
|
19
|
| Cashews,
dry roasted, 1 oz |
73
|
18
|
| Nuts, mixed,
dry roasted, 1 oz |
66
|
17
|
| Spinach,
cooked, 1/2 c |
65
|
16
|
| Bran
flakes, 1/2 c |
60
|
15
|
| Cereal,
oats, instant/fortified,
cooked w/ water, 1 c |
56
|
14
|
| Potato,
baked w/ skin, 1 med |
55
|
14
|
| Soybeans,
cooked, 1/2 c |
54
|
14
|
| Peanuts,
dry roasted, 1 oz |
50
|
13
|
| Peanut
butter, 2 Tbs. |
50
|
13
|
| Chocolate
bar, 1.45 oz |
45
|
11
|
| Vegetarian
baked beans, 1/2 c |
40
|
10
|
| Potato,
baked w/out skin, 1 med |
40
|
10
|
| Avocado,
California, 1/2 med |
35
|
9
|
| Lentils,
cooked, 1/2 c |
35
|
9
|
| Banana,
raw, 1 medium |
34
|
9
|
| Shrimp,
mixed species, raw, 3 oz (12
large) |
29
|
7
|
| Tahini,
2 Tbs |
28
|
7
|
| Raisins,
golden seedless, 1/2 c packed |
28
|
7
|
| Cocoa
powder, unsweetened, 1 Tbs |
27
|
7
|
| Bread,
whole wheat, 1 slice |
24
|
6
|
| Spinach,
raw, 1 c |
24
|
6
|
| Kiwi
fruit, raw, 1 med |
23
|
6
|
| Hummus,
2 Tbs |
20
|
5
|
| Broccoli,
chopped, boiled, 1/2 c |
19
|
5
|
|
*DV = 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 healthful
diet.
|
This
Fact Sheet was developed by the Clinical Nutrition Service, Warren Grant
Magnuson Clinical Center, National Institutes of Health (NIH), Bethesda,
MD, in conjunction with the Office of Dietary Supplements (ODS) in the Office
of the Director of NIH. The mission of ODs is to strengthen knowledge and
understanding of dietary supplements by evaluating scientific information,
stimulating and supporting research, disseminating research results, and
educating the public to foster an enhanced quality of life and health for
the US population. The Clinical Nutrition Service and the ODs would like
to thank the expert scientific reviewers for their role in ensuring the
scientific accuracy of the information discussed in this Fact Sheet.
References
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Ann Emerg Med 1996;28:552-5.
39. Whang R. Clinical disorders of magnesium metabolism. Compr Ther
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Updated 12/9/02
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