Magnesium – Part 2

When can magnesium deficiency occur?

Even though dietary surveys suggest that many Americans do not get recommended amounts of magnesium, symptoms of magnesium deficiency are rarely seen in the US. However, there is concern that many people may not have enough body stores of magnesium because dietary intake may not be high enough. Having enough body stores of magnesium may be protective against disorders such as cardiovascular disease and immune dysfunction.

The health status of the digestive system and the kidneys significantly influence magnesium status. Magnesium is absorbed in the intestines and then transported through the blood to cells and tissues. Approximately one-third to one-half of dietary magnesium is absorbed into the body. Gastrointestinal disorders that impair absorption such as Crohn’s disease can limit the body’s ability to absorb magnesium. These disorders can deplete the body’s stores of magnesium and in extreme cases may result in magnesium deficiency. Chronic or excessive vomiting and diarrhea may also result in magnesium depletion.

Healthy kidneys are able to limit urinary excretion of magnesium to make up for low dietary intake. However, excessive loss of magnesium in urine can be a side effect of some medications and can also occur in cases of poorly-controlled diabetes and alcohol abuse.

Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures (sudden changes in behaviors caused by excessive electrical activity in the brain), personality changes, abnormal heart rhythms, and coronary spasms can occur. Severe magnesium deficiency can result in low levels of calcium in the blood (hypocalcemia). Magnesium deficiency is also associated with low levels of potassium in the blood (hypokalemia).

Many of these symptoms are general and can result from a variety of medical conditions other than magnesium deficiency. It is important to have a physician evaluate health complaints and problems so that appropriate care can be given.

Who may need extra magnesium?

Magnesium supplementation may be indicated when a specific health problem or condition causes an excessive loss of magnesium or limits magnesium absorption.

  • Some medicines may result in magnesium deficiency, including certain diuretics, antibiotics, and medications used to treat cancer (anti-neoplastic medication). Examples of these medications are:
    • Diuretics: Lasix, Bumex, Edecrin, and hydrochlorothiazide
    • Antibiotics: Gentamicin, and Amphotericin
    • Anti-neoplastic medication: Cisplatin
  • Individuals with poorly-controlled diabetes may benefit from magnesium supplements because of increased magnesium loss in urine associated with hyperglycemia.
  • Magnesium supplementation may be indicated for persons with alcoholism. Low blood levels of magnesium occur in 30% to 60% of alcoholics, and in nearly 90% of patients experiencing alcohol withdrawal. Anyone who substitutes alcohol for food will usually have significantly lower magnesium intakes.
  • Individuals with chronic malabsorptive problems such as Crohn’s disease, gluten sensitive enteropathy, regional enteritis, and intestinal surgery may lose magnesium through diarrhea and fat malabsorption. Individuals with these conditions may need supplemental magnesium.
  • Individuals with chronically low blood levels of potassium and calcium may have an underlying problem with magnesium deficiency. Magnesium supplements may help correct the potassium and calcium deficiencies.
  • Older adults are at increased risk for magnesium deficiency. The 1999-2000 and 1998-94 National Health and Nutrition Examination Surveys suggest that older adults have lower dietary intakes of magnesium than younger adults. In addition, magnesium absorption decreases and renal excretion of magnesium increases in older adults. Seniors are also more likely to be taking drugs that interact with magnesium. This combination of factors places older adults at risk for magnesium deficiency. It is very important for older adults to get recommended amounts of dietary magnesium.

Doctors can evaluate magnesium status when above-mentioned medical problems occur, and determine the need for magnesium supplementation.

Table 4 describes some important interactions between certain drugs and magnesium. These interactions may result in higher or lower levels of magnesium, or may influence absorption of the medication.

Table 4: Common and important magnesium/drug interactions

Drug Potential Interaction
  • Loop and thiazide diuretics (e.g. lasix, bumex, edecrin, and hydrochlorthiazide
  • Anti-neoplastic drugs (e.g. cisplatin)
  • Antibiotics (e.g. gentamicin and amphotericin)
These drugs may increase the loss of magnesium in urine. Thus, taking these medications for long periods of time may contribute to magnesium depletion.
  • Tetracycline antibiotics
Magnesium binds tetracycline in the gut and decreases the absorption of tetracycline.
  • Magnesium-containing antacids and laxatives
Many antacids and laxatives contain magnesium. When frequently taken in large doses, these drugs can inadvertently lead to excessive magnesium consumption and hypermagnesemia, which refers to elevated levels of magnesium in blood.