Why Chemo Can Cause Low Magnesium — and How Doctors Treat It

Cashews are a healthy sources of magnesium, an essential mineral that can be low among people going through chemo.
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Magnesium is one of the most essential minerals your body needs. In fact, it's used by every single organ and plays an important role in energy production, according to the U.S. National Library of Medicine.


Your body contains about 25 grams of magnesium, about half of which is found in your bones, according to Oregon State University. The rest is found mostly in muscle tissue. Healthy adults typically need between 310 and 420 milligrams of magnesium a day, depending on their age and sex. Good food sources of magnesium include Brazil nuts, cashews, leafy greens and legumes.

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The normal range for magnesium levels on a blood test is 1.3 to 2.1 milliequivalents per liter or mEq/L, according to the Library of Medicine. But when you're low in magnesium, you might find yourself dealing with fatigue, numbness or muscle cramps, spasms or weakness. Left untreated, complications of a magnesium deficiency can become even more serious, according to Oregon State University. Low magnesium has been linked to higher risks of heart disease, osteoporosis and type 2 diabetes.

Read more: Foods That Are Rich in Magnesium, Potassium and Calcium

How Chemotherapy Can Affect Magnesium Levels

If you're undergoing chemotherapy, the medications themselves could cause your magnesium levels to drop. Cancer patients receiving such chemotherapy drugs as cisplatin, cetuximab, interleukin-2 and cyclosporine may experience a dip in magnesium levels within three weeks of beginning treatment because of the way these drugs affect kidney function, Megan Kruse, MD, an oncologist at the Cleveland Clinic, tells LIVESTRONG.com.


Chemotherapy can also cause diarrhea, according to the American Cancer Society, and chronic diarrhea is a common cause of low magnesium, the Library of Medicine reports.

However, low magnesium from chemo isn't usually a permanent problem. "Though magnesium levels can be low for months after chemotherapy, most levels rebound after treatment," Dr. Kruse says.


Read more: The Nutrients You Need if You Have Low Hemoglobin From Chemotherapy

Your health care provider will likely measure your magnesium levels (as well as levels of other nutrients) through regular blood tests during chemotherapy. "Since low magnesium can be associated with serious cardiovascular arrhythmias, it's very important that we monitor magnesium levels throughout chemotherapy," Kelsey Martin, MD, an oncologist and assistant professor of clinical medicine at Yale School of Medicine, tells LIVESTRONG.com.


"If a patient's magnesium levels are low, we may suggest an oral medication or IV injection," Dr. Martin adds. However, magnesium supplements aren't ideal for every patient: The therapy can also cause diarrhea, so supplementing requires ongoing monitoring, she adds.

Certain people should not use magnesium supplements, including those taking medications for heart disease, high blood pressure or diabetes, according to Memorial Sloan Kettering Cancer Center. Always discuss supplements you're interested in trying with your doctor first, especially during cancer treatment. Getting plenty of this vital nutrient through your diet, on the other hand, has not been linked to any worrisome side effects.

Read more: 3 Ways Vitamin B12 Is Linked to Chemotherapy Side Effects




Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.

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