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Hypomagnesemia (Low Level of Magnesium in the Blood)

by James L. Lewis, III, MD

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

Although blood contains very little magnesium, some is still necessary for normal nerve and muscle function and for development of bone and teeth (see Overview of Magnesium). 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 B, and the chemotherapy drug cisplatin

  • Breastfeeding, which increases requirements for magnesium

Hypomagnesemia may cause loss of appetite, 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 people with alcoholism 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.

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