Magnesium is an essential nutrient, meaning that your body needs it for healthy functioning. It is found in significant quantities throughout the body and used for numerous purposes, including muscle relaxation, blood clotting, and the manufacture of ATP (adenosine triphosphate, the body's main energy molecule).

It has been called nature's calcium channel blocker. The idea refers to magnesium's ability to block calcium from entering muscle and heart cells. A group of prescription heart medications work in a similar way, although much more powerfully. This may be the basis for some of magnesium's effects when it is taken as a supplement in fairly high doses.

Requirements

Requirements for magnesium increase as we grow and age. The official US and Canadian recommendations for daily intake are as follows:

  • Infants
    • 0-6 months: 30 mg
    • 7-12 months: 75 mg
  • Children
    • 1-3 years: 80 mg
    • 4-8 years: 130 mg
  • Males
    • 9-13 years: 240 mg
    • 14-18 years: 410 mg
    • 19-30 years: 400 mg
    • 31 years and older: 420 mg
  • Females
    • 9-13 years: 240 mg
    • 14-18 years: 360 mg
    • 19-30 years: 310 mg
    • 31 years and older: 320 mg
  • Pregnant Women
    • 18 years and younger: 400 mg
    • 19-30 years: 350 mg
    • 31-50 years: 360 mg
  • Nursing Women
    • 18 years and younger: 360 mg
    • 19-30 years: 310 mg
    • 31-50 years: 320 mg

Note: These recommendations refer to total intake from food plus supplements. The average diet provides a daily intake of magnesium very close to these amounts.

Sources

Kelpis very high in magnesium. Other good sources include blackstrap molasses, brewer's yeast (not to be confused with nutritional yeast), and buckwheat. The National Institutes of Health's Office of Dietary Supplements provides this list of other foods that contain magnesium:125

Food Serving size Magnesium content
(milligrams [mg])
% Daily Value
Wheat bran ¼ cup 89 22
Almonds, dry roasted 1 ounce 80 20
Spinach, frozen, cooked ½ cup 78 20
Raisin bran cereal 1 cup 77 19
Cashews, dry roasted 1 ounce 74 19
Soybeans, cooked ½ cup 74 19
Wheat germ ¼ cup 69 17
Mixed nuts, dry roasted 1 ounce 64 16
Bran flakes cereal ¾ cup 64 16
Shredded wheat cereal 2 biscuits 61 15
Fortified instant oatmeal 1 cup 61 15
Peanuts, dry roasted 1 ounce 50 13
Peanut butter 2 tablespoons 49 12
Baked potato (with skin) 1 medium 48 12
Blackeyed peas, cooked ½ cup 46 12
Pinto beans, cooked ½ cup 43 11
Brown rice, cooked ½ cup 42 11
Lentils, cooked ½ cup 36 9
Vegetarian baked beans ½ cup 35 9
Kidney beans, canned ½ cup 35 9
Magnesium Deficiency

In the United States, the average dietary intake of magnesium is lower than the recommended daily allowance; however, it is unclear whether this truly indicates deficiency, or if the recommended allowance is too high.1,2Alcohol abuse, surgery, diabetes, zinc supplements, certain types of diuretics ( thiazide and loop diuretics, but not potassium-sparing diuretics), estrogen and oral contraceptives, and the medications cisplatin and cyclosporinhave been reported to reduce the body's level of magnesium or increase magnesium requirements.3,4,5,88-92 If you are taking potassium supplements, you may receive greater benefit from them if you take extra magnesium as well.

Magnesium Absorption

While it is sometimes said that calciuminterferes with magnesium absorption, this effect is apparently too small to have a significant effect on overall magnesium status.8,9