The adult human body contains approximately 20 to 28 g of magnesium, of which 60% is found in bones, 26% in muscles, and the remainder in soft tissues and body fluids. Gender differences in the body content of magnesium begin before puberty.
Magnesium plays a role in neuromuscular transmission and activity. Working in concert with and against the effects of calcium, depending on the system involved. In a normal muscle contraction, calcium acts as a stimulator, and magnesium acts as a relaxant. Magnesium acts as a physiologic calcium-channel blocker.
High magnesium intakes are associated with greater bone density. Large doses of magnesium can result in central nervous system depression, anesthesia, even paralysis, especially in patients with renal insufficiency. Patients with renal problems should not be given magnesium supplements.
Oral magnesium supplementation in middle-age and older women with mild to moderate hypertension was found to reduce systolic and diastolic blood pressure significantly. Low magnesium intakes have been associated with coronary heart disease.
Dietary reference intake
Infants 30-75 mg/day
Children 80-130 mg/day
Adolescents 240-410 mg/day
Adults 310-400 mg/day
Pregnant 350-400 mg/day
Lactating 310-360 mg/day
Magnesium content of selected foods
Halibut, baked, ½ fillet (170 mg)
Spinach, canned, 1 cup (163 mg)
Cow peas, cooked, 1 cup (91 mg)
Muffin, oat bran, 1 (89 mg)
Rice, brown, cooked, 1 cup (84 mg)
Cashews, roasted, 1 oz (77 mg)
Orange juice, 6 oz (72 mg)
Mixed nuts, roasted, 1 oz (67 mg)
Baked potato with skin, 1 (57 mg)
Raisins, 1 cup (46 mg)
Bread, whole wheat, 1 slice (29 mg)
Milk, 2% fat, 1 cup (27 mg)
Excess magnesium can inhibit bone calcification.