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.
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.
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
1-3 years – 65 mg/day
4-8 years – 110 mg/day
Adults – 350 mg/day
The Daily Reference Intakes (DRI) for magnesium are shown in the table below.
Magnesium requirements Daily Reference Intakes
0-6 months – 30 mg
7-12 months – 75 mg
1-3 years – 80 mg
4-8 years – 130 mg
9-13 years – 240 mg
14-18 years – 410 mg
19-30 years – 400 mg
>31 years – 420 mg
9-13 years – 240 mg
14-18 years – 360 mg
19-30 years – 310 mg
>31 years – 320 mg
>18 years – 400 mg
19-30 years – 350 mg
31-50 years – 360 mg
<18 years – 360
19-30 years – 310
31-50 years – 320
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
Pumpkin seeds, 1/4 cup roasted – 303 mg
Almonds, 1/2 cup – 238 mg
Soy nuts, 1/2 cup – 196 mg
Cashews, 1/2 cup – 157 mg
Tofu, firm, 1/2 cup – 128 mg
Peanuts, 1/2 cup – 125 mg
Chili with beans, 1 cup – 115 mg
Molasses, 2 Tbl – 100 mg
Wheat germ, toasted, 2 Tbl – 90 mg
Unsweetened chocolate, 50 g – 155 mg
Sunflower seeds, 1/4 cup – 82 mg
Halibut, baked, 100 g – 92 mg
Swiss chard, cooked, 1/2 cup – 75 mg
Spinach, 1/2 cup cooked – 66 mg
Black beans, 1/2 cup – 60 mg
Oatmeal, 1 cup cooked – 56 mg
Peanut butter, 2 Tbl – 51 mg
Baked potato with skin – 55 mg
Cereal, raisin bran, 50 g – 85 mg
Low fat yogurt, 1 cup – 43 mg
Milk, nonfat, 1 cup – 28 mg
Chicken, breast, 100 g. – 30 mg
Green peas, cooked, 1/2 cup – 23 mg