Magnesium

What is it?
Magnesium is a mineral that forms part of the bone matrix. Its level in the blood is regulated by the kidneys.

What does it do?
Magnesium is important to the body in a number of ways. It plays a part in:

• bone metabolism
• the transmission of nerve impulses to muscles
• transporting calcium and potassium
• getting energy from the carbohydrates we eat
• the production of body proteins and DNA
• regulating blood pressure (in conjunction with calcium and potassium)

Magnesium also has been correlated with bone mineral density in post-menopausal women.

Where do you get it?
Magnesium occurs widely in foods and drinking water (except soft water). The highest amounts are in nuts, legumes and whole grains. Green vegetables are also good sources.

Magnesium in Foods

Food	Amount	Milligrams of Magnesium
All-bran cereal	8 oz. (1 cup)	318
Soybean nuts, roasted	4 oz. (1/2 cup)	196
Pumpkin seeds, roasted	1 oz.	152
Tofu	4 oz. (1/2 cup)	127
Navy beans, canned	8 oz. (1 cup)	122
Lima beans, canned	8 oz. (1 cup)	94
Almonds	1 oz.	86
Cooked spinach	4 oz. (1/2 cup)	78
Kidney beans, canned	8 oz. (1 cup)	74
Lentils, cooked	8 oz.(1 cup)	71
Bran flakes	8 oz.(1 cup)	70
Potato with skin	1 medium potato	55
Peanut butter	2 tbsp.	51
Okra, boiled	4 oz. (1/2 cup)	46
Peas, cooked or frozen	4 oz. (1/2 cup)	23
Green beans, cooked or frozen	4 oz. (1/2 cup)	15

One of the highest sources of magnesium is not a food at all; it is milk of magnesia taken as a laxative. Just two tablespoons provide 1,000 milligrams, which is more than twice as much as the Recommended Dietary Allowance (RDA) for anyone of any age. This is not necessarily a good thing; taken too frequently, it could be toxic. Milk of magnesia also decreases the availability of calcium and phosphorus.

How much do we need?
The RDA for magnesium is different for men and women, and different amounts are needed at different ages.

Gender	Age	Amount Required (milligrams)
Men	19-30	400
Men	31-70	420
Pregnant women	18 and under	400
Pregnant women	19-30	350
Pregnant women	31-50	360
Women	19-30	310
Women	31-70	320

We usually absorb about half the magnesium we need from food; the presence of phytate and fiber reduce absorption to a minor extent.

If you eat about three servings of vegetables a day, have legumes two or three times a week, and get six to 10 servings of whole grains a day, it should be fairly easy to get enough magnesium from foods. However, the typical fast-food and refined diet of many Americans generally does not provide enough of this mineral.

In unusual medical circumstances, such as life-threatening convulsions or severe eclampsia of pregnancy, it may be necessary to provide supplementary magnesium by injection.

Is it safe?
Magnesium is safe in the appropriate amounts. However, as mentioned earlier, it can be toxic in excessive amounts. Milk of magnesia, which provides 1,000 milligrams of magnesium in just two tablespoons, is a commonly used, potentially toxic source. Elderly people who use it frequently as a laxative could be at risk for magnesia intoxication because their aging kidneys may not function well enough to clear it as well as a younger person's kidneys. Some of the signs of magnesium intoxication include:

• drowsiness
• lethargy
• sweating
• slurred speech

The upper limit for safe ingestion of magnesium from supplements and pharmacological sources is 350 milligrams a day. (This maximum does not include any of the magnesium obtained from food and water.)