The main reason to take a magnesium supplement is a documented low body magnesium, usually identified by a low blood level. A normal blood level range is 1.7 to 2.2 milligrams per deciliter. To maintain a healthy magnesium level, it’s best to get the mineral from food, especially dark, leafy green vegetables, unrefined grains, and legumes. The recommended dietary allowance (RDA) of magnesium from food is 420 milligrams (mg) per day for men ages 50 and older and 320 mg/day for women ages 50 and older. The RDA for magnesium from a supplement is lower: 350 mg/day for men and women.
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