Magnesium is used to treat a variety of health conditions. People with diabetes may lose excessive amounts of magnesium in the urine and require supplementation. Alcoholics are also often deficient in magnesium. Over-the-counter magnesium is used to treat constipation and heartburn. Normally, the kidneys excrete extra magnesium efficiently. In people with kidney failure, medically termed renal failure, the kidneys can’t excrete enough magnesium and serum levels may climb too high. People with kidney failure should not take extra magnesium without their medical practitioner’s approval.
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Food sources rarely raise magnesium above normal limits. Taking extra magnesium in the form of over-the-counter milk of magnesia to treat heartburn, indigestion or constipation, or for use as a weight-loss laxative can cause magnesium levels to rise even in healthy persons. Over-the-counter medications are not without risk; follow the directions for dosing on the bottle and do not exceed amounts listed even if you don’t have impaired renal function. Even moderate amounts of over-the-counter laxative and heartburn preparations can cause high magnesium levels, the Linus Pauling Institute warns. Magnesium supplements should not be taken unless ordered by your physician.
Renal Failure Effects
The nephrons in the kidney contain filtering units called glomeruli. The kidneys normally filter 70 to 80 percent of the magnesium in the blood and excrete around 6 percent, according to Carol Mattson Porth, author of “Essentials of Pathophysiology: Concepts of Altered Health States.” Most of the magnesium is absorbed in the thick ascending loop of Henle, part of the tubule system that attaches to the glomeruli. When filtering units in the kidney or any part of the tubules are damaged, more magnesium stays in the blood.
The normal level of magnesium in the blood falls below 2.6 mg/dL. Symptoms don’t usually appear until levels rise above 4.8 mg/dL, Port reports. Symptoms of hypermagnesemia include muscle weakness, nausea, vomiting, diarrhea, mental depression, low blood pressure, confusion, lethargy, decreased respiration, loss of deep tendon reflexes and heart block. In severe cases, cardiac arrest can occur. Stop taking magnesium if any symptoms of toxicity appear.
The elderly often have decreased kidney function and are more likely to develop magnesium toxicity by taking laxative and antacids containing magnesium even if they aren’t in renal failure. Since renal failure may not have any overt signs until significant loss of kidney function has occurred, elderly people should not take more than 350mg of magnesium per day without medical approval.