Bone contains most of the body's magnesium. Blood contains very little. Magnesium is necessary for the formation of bone and teeth and for normal nerve and muscle function. Many enzymes in the body depend on magnesium to function normally. The body obtains magnesium from foods and excretes it in urine and stool.

Hypomagnesemia

In hypomagnesemia, the level of magnesium in blood is too low.

Usually, the level becomes low because people consume less (most often, because of starvation) or because the intestine cannot absorb nutrients normally (called malabsorption). But sometimes hypomagnesemia develops because the kidneys or intestine excrete too much magnesium. Hypomagnesemia may result from the following:

• Consuming large amounts of alcohol (common), which reduces consumption of food (and thus magnesium) and increases excretion of magnesium
• Protracted diarrhea (common), which increases excretion
• High levels of aldosterone, antidiuretic hormone, or thyroid hormones, which increase excretion
• Drugs that increase excretion, including diuretics, the antifungal drug amphotericin BSome Trade Names
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• Breastfeeding, which increases requirements for magnesium

Hypomagnesemia may cause nausea, vomiting, sleepiness, weakness, personality changes, muscle spasms, tremors, and loss of appetite. If severe, hypomagnesemia can cause seizures, especially in children.

The diagnosis is usually based on blood tests indicating that the magnesium level is low.

Magnesium is given by mouth when the deficiency causes symptoms or persists. All alcoholics are given magnesium. If a very low magnesium level is causing severe symptoms or if people cannot take magnesium by mouth, magnesium is given by injection into a muscle or vein.

Hypermagnesemia

In hypermagnesemia, the level of magnesium in blood is too high.

Hypermagnesemia usually develops only when people with kidney failure are given magnesium salts or take drugs that contain magnesium (such as some antacids or laxatives).

Hypermagnesemia may cause weakness, low blood pressure, and impaired breathing. When hypermagnesemia is severe, the heart can stop beating.

The diagnosis is based on blood tests indicating that the magnesium level is high.

People with severe hypermagnesemia are given calcium gluconate intravenously. Diuretics (particularly if given intravenously) can increase the kidneys' excretion of magnesium. However, if the kidneys are not functioning well (as is typical) or if hypermagnesemia is severe, dialysis is usually needed.

Last full review/revision August 2008 by Larry E. Johnson, MD, PhD