Cancer Treatments Often Lower Magnesium Levels

Finding the best magnesium supplement for cancer patients isn’t straightforward. The right form and dose depend on the patient’s treatment, kidney function, and other medications. Two doctors explain why cancer treatment often lowers magnesium, which symptoms to watch for, and how to choose a supplement safely.

Cancer patients face a higher risk of low magnesium, though the cancer itself isn’t always the cause. Amar Rewari, MD, chief of radiation oncology at Luminis Health, notes that treatments, poor nutrition, vomiting, diarrhea, or kidney problems can all contribute to deficiency.

Which Treatments Lower Magnesium?

Certain cancer treatments are more likely to reduce magnesium levels. Cisplatin, a platinum-based chemotherapy drug, is known for causing the kidneys to lose magnesium, sometimes for months after treatment. According to 2020 research, 40% to 90% of patients receiving cisplatin experience low magnesium.

Targeted therapies like cetuximab and other EGFR inhibitors can also reduce magnesium by affecting kidney regulation. Studies show 26% to 37% of patients on cetuximab develop low magnesium, with 3% to 6% experiencing severe cases.

Symptoms and Diagnosis

Mild magnesium deficiency may not cause noticeable symptoms. As levels drop, patients may experience muscle cramps, weakness, fatigue, tremors, nausea, numbness, irregular heartbeat, or loss of appetite. These symptoms can resemble treatment side effects, so informing the oncology team is important.

Deficiency is usually confirmed with a blood test, though blood levels don’t always reflect total magnesium stores. Oncology teams often monitor magnesium as part of routine lab work, especially for patients on medications known to lower it.

Unlike earlier approaches, today’s care teams proactively monitor magnesium levels, particularly for patients on high-risk treatments like cisplatin. This shift reflects a broader understanding of how nutritional deficiencies impact treatment outcomes.

If deficiency is found, treatment may include oral supplements, intravenous magnesium, or addressing the underlying cause. However, supplements must be used carefully, especially in patients taking other systemic medications.

Catherine Perrault, DO, chief medical officer at The Mesothelioma Center, emphasizes that magnesium supplements should not interfere with treatment or worsen health. For example, magnesium can cause diarrhea, increasing dehydration risk in patients already struggling with nausea.

There’s no single best form for everyone. Magnesium glycinate is often better tolerated, while citrate and oxide are more likely to cause diarrhea. The choice depends on the patient’s symptoms and needs.

Magnesium can alter the absorption and efficacy of other medications. Patients should work with their physician and pharmacist to determine when to take supplements relative to their treatment schedule.

High intakes from supplements can cause diarrhea, nausea, and abdominal cramping, with an upper limit of 350 mg from supplements alone.

Eating magnesium-rich foods like pumpkin seeds, spinach, and whole grains may suffice to maintain normal levels. If levels remain low, oral or intravenous supplements may be needed. A registered dietitian can help plan meals, especially when side effects make eating difficult.

Magnesium Supplements and Interactions

Magnesium supplements can interact with medications, affecting their absorption and efficacy. Dr. Perrault notes that while magnesium doesn’t cancel chemotherapy, it can still impact the body. Patients should coordinate with their physician and pharmacist to determine the best timing for supplements relative to treatment.

Dietary Sources and Professional Guidance

In some cases, dietary changes alone can maintain normal magnesium levels. Foods rich in magnesium include pumpkin seeds, chia seeds, cashews, black beans, edamame, avocado, spinach, peanut butter, and whole grains. Dr. Perrault recommends trying these foods first and rechecking blood levels after four to six weeks.

The National Institutes of Health Office of Dietary Supplements (ODS) notes that healthy kidneys remove excess magnesium through urine, but impaired kidney function increases the risk of magnesium buildup. This shows the importance of monitoring kidney health in cancer patients considering magnesium supplementation.