| Nutrition Fact Sheet: Magnesium |
Physiological Functions
Magnesium has roles in energy metabolism, muscle contraction, and nerve impulse transmission, and bone mineralization. It is a required cofactor for an estimated 300 enzymes. Among the reactions catalyzed by these enzymes are fatty acid synthesis, protein synthesis, and glucose metabolism. Magnesium status is important for regulation of calcium balance through parathyroid hormone-mediated reactions. Secretion of parathyroid hormone and end-organ responsiveness to the hormone are dependent on availability of the mineral.
As a positively charged divalent cation, magnesium acts as a calcium antagonist at the cell membrane level which is necessary to maintain normal electrical potentials and to coordinate muscle contraction-relaxation responses. In muscle, increased intracellular calcium concentration triggers contraction while increased intracellular magnesium concentration counteracts this effect resulting in relaxation. Magnesium is also involved in metabolism of ATP which enables release of energy stored in the high-energy phosphate ester bond. It is also a potent vasodilator. Magnesium and calcium coordinate the constriction/relaxation of capillary blood vessels which contributes to regulation of blood pressure.
Factors Affecting Availability
Milling of whole grains reduces the magnesium content of the processed flour to 20% of the amount initially present. High intakes of calcium can inhibit magnesium absorption.
Deficiency
Magnesium deficiencies are usually observed as secondary to other clinical conditions rather than due to inadequate dietary intake. Use of diuretics, alcohol abuse, renal disease, and acidosis can contribute to magnesium deficiency through increasing urinary losses. Symptoms of magnesium deficiency include tremors, muscular weakness, confusion, nervousness, hallucinations and swallowing difficulties.
Toxicity
Exposure to magnesium from dietary sources is unlikely to result in toxicity. Individuals who take magnesium-containing laxatives may experience diarrhea without any other adverse effects.
Since magnesium balance is regulated by renal mechanisms, patients with renal disease are prone to toxicity. Initial symptoms of magnesium toxicity include diarrhea, nausea, vomiting, and low blood pressure. Advanced stages of toxicity are characterized by cardiovascular and muscular irregularities.
The upper limit of safety for magnesium established by the Food and Nutrition Board of the Institute of Medicine is approximately 350 mg daily for adults. See table below for more age- and gender specific guidelines.
Magnesium Tolerable Upper Intake Levels
Life Stage Magnesium(mg/day)
Infants
0-6 mo N/A
7-12 mo N/A
Children
1-3 years 65
4-8 years 110
Males, Females
9-13 years 350
14-18 years 350
19-70 years 350
>70 years 350
Pregnancy
< 18 years 350
19-50 years 350
Lactation
< 18 years 350
19-50 years 350
Requirements
The Daily Reference Intakes (DRI) for magnesium are shown in the table below.
Magnesium Requirements Daily Reference Intakes
Life Stage Magnesium (mg)
Infants
0-6 mo 30
7-12 mo 75
Children
1-3 years 80
4-8 years 130
Males
9-13 years 240
14-18 years 410
19-30 years 400
31-50 years 420
51-70 years 420
>70 years 420
Females
9-13 years 240
14-18 years 360
19-30 years 310
31-50 years 320
51-70 years 320
>70 320
Pregnancy
>18 years 400
19-30 years 350
31-50 years 360
Lactation
<18 years 360
19-30 years 310
31-50 years 320
Dietary Sources
Rich sources of magnesium include nuts and seeds, soybeans, tofu, chocolate, dark-green vegetables, legumes, yogurt, wheat germ and dairy products. See table below for detailed listing.
Magnesium Content of Food
Food Magnesium (mg)
Pumpkin seeds, 1/4 cup roasted 303
Almonds, 1/2 cup 238
Soy nuts, 1/2 cup 196
Cashews, 1/2 cup 157
Tofu, firm, 1/2 cup 128
Peanuts, 1/2 cup 125
Chili with beans, 1 cup 115
Molasses, 2 Tbl 100
Wheat germ, toasted, 2 Tbl 90
Unsweetened chocolate, 1 oz 88
Sunflower seeds, 1/4 cup 82
Halibut, baked, 3 oz. 78
Swiss chard, cooked, 1/2 cup 75
Spinach, 1/2 cup cooked 66
Black beans, 1/2 cup 60
Oatmeal, 1 cup cooked 56
Peanut butter, 2 Tbl 51
Baked potato with skin, 1 55
Cereal, raisin bran, 1 oz. 48
Low fat yogurt, 1 cup 43
Milk, nonfat, 1 cup 28
Chicken, breast, 3 oz. 25
Green peas, cooked, 1/2 cup 23
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