In part one of this article, “Magnesium and Kidneys,” I discussed the increased prevalence of magnesium deficiency and addressed the question: “Can magnesium help kidney function?” Magnesium is the fourth most abundant mineral in the body. It is essential for many biological functions. As I discussed in part one, magnesium is also crucial for kidney health. Here, in part two of our discussion on magnesium and the kidneys, I discuss the reasons for magnesium deficiency and the current literature on measuring and supplementing magnesium in people with chronic kidney disease (CKD).

Magnesium Deficiency: Assessment and Management for Better Kidney Health

Causes of magnesium deficiency

Poor dietary choices

There has been a steady decline in magnesium content in cultivated fruits and vegetables over the past 100 years. This is caused by the depletion of magnesium in soil over time. In addition, utilizing phosphate-based fertilizers leads to the formation of magnesium phosphate salts that are not soluble. This means the soil is deprived of both components: magnesium and phosphorus.

On top of that, the rise of ultra-processed food and drinks have also contributed to the depletion of magnesium in the modern standard American diet. Grain bleaching and vegetable cooking and adding preservatives can lead to a significant loss of magnesium content. Preservatives such as various forms of phosphate and oxalate can bind with magnesium and prevent its absorption. Phosphoric acid in soft drinks has similar effects.

The addition of fluoride to drinking water also prevents magnesium absorption by binding to it and forming insoluble complexes. Finally, drinking caffeine and alcohol can also lead to an increase in the excretion of magnesium by the kidneys, causing magnesium deficiency.

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Drug-induced magnesium deficiency

Many medications can interfere with magnesium absorption or increase its excretion, leading to deficiency. Most of the medications leading to magnesium deficiency are summarized in the following table:

Medication class Example Mechanism
Anti-diabetic medications Insulin, insulin mimetics Interferes with Na/Mg exchange leading to renal loss
Antimicrobial Gentamicin, pentamidine, foscarnet, amphotericin B Increased renal loss
Beta agonists Salbutamol Renal loss and cellular shifts
Bisphosphonate Pamidronate Renal loss
Cardiac glycoside Digoxin Increased renal loss
Chemotherapy agents Cisplatin Renal loss
Diuretics Thiazide diuretics Renal loss
Proton-pump inhibitors Omeprazole Decreased GI absorption

Measuring magnesium status

Simply put, there is no ideal test for assessing magnesium status in the body. Mg blood levels are tightly controlled and represent only 0.8% of total body stores (0.5% in red blood cells and 0.3% in the serum). Red blood cell Mg levels have been used as an alternative method, but this too does not represent total body stores and is not well validated. Measuring urine Mg requires measuring a 24-hour urine specimen. This too has been found to be imperfect due to large variations from day to day.

The Mg retention test has been proposed as a more accurate way to assess Mg status. Here, the patient receives an intravenous Mg load (0.25 mmol magnesium/kg body weight at a rate of 2.5 mmol/hour), and a 24-hour urine specimen is collected before and after the load. The percentage of administered magnesium that is retained by the body (not excreted in urine) determines magnesium status. This test is not standardized yet, but retention of 25%-50% may indicate a moderate deficiency, and retention of more than that may indicate severe deficiency.

Ideally, measuring muscle or bone magnesium may be more reflective of accurate magnesium stores but this is obviously not practical. Combining a serum Mg test, a 24-hour urinary Mg, and assessing dietary Mg intake is the most comprehensive and practical evaluation of a patient’s magnesium status.

Patients at high risk for magnesium deficiency include:

  • Diabetics
  • Heart disease patients
  • Osteoporosis patients
  • People who eat a diet high in processed food and soda
  • People who suffer from leg cramps
  • People with metabolic syndrome
  • People who take certain medications

Those patients at risk of magnesium deficiency should be targeted for additional testing and supplementation.

What type of magnesium should I take?

The type of magnesium supplement used depends on the exact indication. Magnesium supplements are available as oxide, hydroxide, gluconate, chloride, citrate, lactate, malate, taurate, L-threonate, sulfate, glycinate, orotate, and carbonate salts. In addition to magnesium citrate’s direct effects on kidney stones, magnesium benefits the person with kidney disease through its effects on blood pressure, insulin sensitivity, vascular health, and bone. The following indications are listed with the recommended types of magnesium supplements and doses. These doses are for prevention only. Patients who are deficient may need higher doses. Magnesium supplements should be discontinued or decreased in kidney patients if the serum magnesium level is higher than 2.6.

Indication Mg type Dose
Prevention of kidney stones Magnesium citrate 400 mg daily
Bone health Magnesium citrate or chloride 400 mg daily
Improving blood pressure Magnesium taurate 400 mg once or twice daily
Improving insulin sensitivity Magnesium taurate 400 mg once or twice daily
Improving vascular health Magnesium glycinate or orotate 200-400 mg daily
Phosphate binder Magnesium carbonate 250 mg with meals

We recommend using high-quality supplements. This article can be a useful guide.

The bottom line

Magnesium is essential to many biological functions, as I described in part one, “Magnesium and Kidneys.” It has many health benefits for kidney, bone, and vascular health. Assessing magnesium status is difficult but magnesium deficiency is very common and underrecognized. Supplementing magnesium may be important for patients with kidney disease. The type of supplement used depends on the indication. As always, it is recommended that you check with a Functional or Integrative Medicine provider and nephrologist before taking any new supplement.