Magnesium (Mg) is one of the most important minerals in the body. It plays an essential role as a cofactor for more than 300 critical enzymatic reactions. Unfortunately, dietary magnesium intake in developed countries has decreased over the past decades due to the increased consumption of low-magnesium diets that include processed foods and produce cultivated in magnesium-depleted soil. Therefore, it is estimated that more than half of the US population does not meet the average requirement of dietary intake of magnesium.
Low magnesium levels have been associated with a number of adverse events, such as high risk for heart disease. However, little is understood about magnesium and kidney health. Here, we will discuss the potential benefits of magnesium on the kidneys. This is one of two articles on magnesium and kidneys. For more on how to test and treat kidney patients with magnesium deficiency, see part two, “Magnesium Deficiency: Assessment and Management for Better Kidney Health.”
Dietary sources of magnesium
A daily intake of 3.6 mg/kg is necessary to maintain magnesium balance in humans under normal conditions. This is estimated to be between 320 to 420 mg/day (13–17 mmol/day) for adults. Sadly, there has been a steady decline in magnesium content in cultivated fruits and vegetables over the past 100 years. This is due to depletion of magnesium in soil over time. This, along with the rise of ultra-processed food, sodas, and taking medications such as proton pump inhibitors and diuretics that deplete magnesium levels (polypharmacy), has led to rising prevalence of magnesium deficiency.
Traditionally, the highest food sources of magnesium are:
- Leafy greens (78 mg/serving on average)
- Nuts (80 mg/serving on average)
- Pumpkin seeds have the highest level of magnesium per serving (156 mg).
- Whole grains (46 mg/serving on average)
A complete list of foods high in magnesium can be found here.
Can Magnesium Help Kidney Function?
There are many potential benefits of magnesium for kidney health including improving blood pressure control, insulin sensitivity, bone health, vascular health, and preventing kidney stones. Let’s explore the data.
Magnesium and blood pressure control
Magnesium supplementation may help reduce blood pressure (BP) by increasing the production of nitric oxide. Nitric oxide acts as a signaling molecule that helps relax blood vessels, which lowers BP. In fact, a review of 34 studies showed that supplementing magnesium with an average dose of 368 mg per day for 3 months can decrease systolic BP by 2.00 mmHg and diastolic BP by 1.78 mmHg. This supplementation was accompanied by 0.05 mmol/L increase in serum magnesium levels.
Magnesium and insulin sensitivity
Diabetes is one of the major risk factors for kidney disease worldwide. Higher dietary intake of magnesium has been correlated with lower diabetes incidence. A review of 18 studies in people with diabetes showed that magnesium supplements reduced fasting plasma glucose levels. In people who are at high risk for diabetes, magnesium supplementation significantly improved plasma glucose levels after a 2-hour oral glucose tolerance test. These effects are thought to be due to the effects of magnesium on insulin receptors and signaling that allows for improvement in glucose transport and utilization.
Magnesium and vascular health
Magnesium levels have been associated with a lower incidence of cardiovascular disease. In fact, supplementing with magnesium was associated with improvement in vascular flow and endothelial function. Endothelial function refers to the lining of the blood vessels, which is involved in regulating blood vessel health and blood clotting.
Studies in patients receiving dialysis have shown that having a lower serum magnesium level is a significant risk for cardiovascular mortality. Laboratory data show that magnesium inhibits high phosphate-induced calcification of vascular smooth muscle cells. Calcification of arteries is a strong predictor of heart disease and heart-disease-related death.
Magnesium and vitamin D
Magnesium is essential to vitamin D metabolism. Vitamin D that we eat or make in our skin from sun exposure circulates in the blood and is bound to vitamin D binding protein (VDBP). VDBP binding activity depends on adequate magnesium levels. In addition, magnesium is an essential cofactor for the enzymes that activate vitamin D. Studies have demonstrated that magnesium deficiency is associated with impaired vitamin D metabolism.
On the other hand, taking large doses of vitamin D can induce severe depletion of magnesium. This is thought to be due to the overutilization of magnesium. Therefore, adequate magnesium supplementation should be an important part of vitamin D therapy.
Magnesium and bone health
Besides magnesium’s effects on vitamin D metabolism, it is an essential component of hydroxyapatite, an essential component of bone and teeth. In fact, 60% of total Mg is stored in the bone. Low magnesium intake was found to be associated with lower bone mineral density in postmenopausal women. Magnesium deficiency contributes to osteoporosis directly by acting on crystal formation and on bone cells and indirectly by impacting the secretion and the activity of parathyroid hormone (PTH) and by promoting oxidative stress and inflammation.
In addition, a review of 8 studies looked at magnesium and chronic kidney disease (CKD). The study investigated magnesium supplementation on parameters of CKD-related mineral bone disease (CKD-MBD). Mg supplementation improved PTH levels and carotid intima-media thickness (CIMT). Low serum Mg levels were also found to impact PTH and worsen osteoporosis in CKD patients, particularly with diabetes.
Magnesium and kidney stones
Mg acts as an inhibitor of calcium oxalate crystallization and stone formation in the urine. It also decreases the absorption of dietary oxalate in the gut. Mg supplementation in patients with kidney stones was found to decrease the incidence of stone formation even in patients without signs of Mg deficiency.
Magnesium as a phosphate binder
Hyperphosphatemia (high phosphate level) is common in advanced kidney disease. Many kidney patients with stage 4 and above use binders that bind phosphate (or “phosphorus,” as it is commonly known) in the food and prevent it from getting absorbed. High phosphate levels have been associated with poor bone and vascular health in kidney patients. In fact, higher dietary phosphate load can be seen in earlier stages of CKD, and it can do harm even before it is detected.
Magnesium carbonate has been successfully used as a phosphate binder. Magnesium based phosphate binders were also found to reduce vascular calcifications in rats with kidney disease. Iron-magnesium hydroxycarbonate was also studied and found to be well tolerated and can effectively lower phosphate levels in dialysis patients. It is essential to know that most of the magnesium used as a phosphorus binder will not be absorbed.
The bottom line on magnesium and kidneys
Magnesium is essential to many biological functions. It has many health benefits for kidney, bone, and vascular health. Optimizing magnesium status is, therefore, an important step in the integrative approach to kidney health. In part two of this blog, “Magnesium Deficiency: Assessment and Management for Better Kidney Health,” we will discuss practical steps for figuring out a person’s actual magnesium status, the best form of magnesium to take, and the dose I recommend for each condition.
