Magnesium and The Kidneys: Adding it in a Renal Diet

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While magnesium is not as popular a topic as, say, potassium is in a renal diet, it can be just as important for kidney patients. When it comes to magnesium and the kidneys, both high and low levels of magnesium can occur with abnormal kidney function. This article will cover magnesium in a renal diet, magnesium supplements, and how to know you’re getting the right amount of magnesium with kidney disease.

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What is Magnesium?

Magnesium is a mineral. It is similar to other minerals like sodium and potassium. 

It is the fourth most abundant mineral in the human body.

Roles of Magnesium

Magnesium plays many important roles in the human body, including;

  • Nerve function
  • Muscle contractions
  • Keeps bones healthy
  • Balances blood sugar
  • Supports immune system
  • Regulate heart beat
  • Make DNA

Magnesium Stored in The Body

Different parts of our body stores magnesium. In particular, our bones, muscle tissues, and soft tissues hold our magnesium stores.

Over 50% of magnesium is stored in our bones (1).

Magnesium Removal from The Body

Excess magnesium from our diet and supplements is removed in our urine and feces.

Those with normal kidney function filter about 1,800 to 2,400 milligrams (mg) of magnesium daily (2).

Magnesium Lab Values

The goal range for magnesium in blood test results is 0.5 – 2.0 mmol/L or 1.0 – 4.9 mg/dL (3).

Different labs may have slightly different ranges. It is important to discuss your lab results with your physician.

High Magnesium Levels

High magnesium levels, also known as hypermagnesemia, can occur in later stages of kidney disease. It is also more common for those on dialysis (4).

This can occur when not enough magnesium is removed via the gut and kidneys.

Low Magnesium Levels

Hypomagnesemia is the term for low magnesium levels. 

Those with late stages of kidney disease (stages 4 and 5) have a higher risk of low magnesium levels (5).

Additionally, medications like diuretics and proton pump inhibitors (PPIs) can cause low magnesium levels (6). These medications are commonly used with kidney patients, so magnesium testing can be vital.

This is important because those with low magnesium levels have a higher risk of worsening kidney damage (7).

Symptoms of High or Low Magnesium

Symptoms of high magnesium levels generally occur at severe levels of high magnesium, greater than 12 mg/dL.

Mild symptoms can include

  • Muscle weakness
  • Fatigue
  • Nausea
  • Dizziness
  • Confusion
  • Decreased reflexes
  • Bladder paralysis
  • Flushing
  • Headache
  • Constipation

Severe symptoms can include

  • Blood pressure drop
  • Bradycardia (slow heart rate)
  • Blurred vision
  • Muscle paralysis
  • Decreased breathing rate

In cases of extreme high magnesium levels (over 15 mg/dL), coma and cardiorespiratory arrest may happen (8).

Magnesium and the Kidneys

Magnesium is very important for kidney patients.

Those with advanced kidney disease may see a rise in magnesium levels. This is because the kidneys become less effective in removing magnesium from the body (9).

Those with a creatinine clearance below 10 mL/min may have high magnesium levels (10).

However, those with a creatinine clearance of 30 mL/min and above can maintain normal magnesium levels (11).

Magnesium and the Renal Diet

Magnesium intake is often lower with kidney patients as many limit foods high in potassium, which are often also high in magnesium.

However, getting adequate magnesium can help protect kidneys from further damage (12).

Why is Magnesium Important for Kidney Disease?

When it comes to magnesium and the kidneys, it can be a tricky situation. This is because people with kidney disease can experience either high or low magnesium levels.

Type 2 Diabetes

People with type 2 diabetes are at higher risk of lower magnesium levels. However, those with both type 2 and diabetes can experience high magnesium as well (13).

A meta-analysis published in 2006 found patients with type 2 diabetes on a magnesium supplement helped lower plasma fasting glucose levels (14).

For those with both CKD and type 2 diabetes, it can be important to have magnesium levels checked routinely.

Blood Pressure

Magnesium supplementation has been shown to lower both systolic and diastolic blood pressure (15).

Additionally, magnesium can help prevent vascular calcification, a common product of end-stage kidney failure (16).

Blood pressure can be more difficult to control when the arteries harden over time due to this calcification.

Bone Health

We often think about calcium when it comes to bone health. However, magnesium plays an important role as well.

Kidney patients are more prone to secondary hyperparathyroidism (sHPT). This is because of the interaction between the kidneys and the parathyroid.

Low magnesium levels have been linked to low calcium and therefore higher parathyroid hormone levels (17).

How Much Magnesium Should A Renal Diet Have?

According to the National Institutes of Health (NIH), magnesium guidelines for adults are 400 – 420 milligrams (mg) per day for men and 310 – 320 mg per day for women.

There are no other specific ranges for kidney patients outside of these recommendations.

However, adjusting dietary intake of magnesium may be necessary if blood levels are out of range.

Tracking Magnesium Intake

We recommend using a food tracker like Cronometer.*

By logging your food, you will be able to see how much your magnesium intake totals daily.

This is a helpful starting point to determine if you are eating enough or too much magnesium and can be used when discussing your blood test results with your doctor.

Alternatively, you can use a food log when working with a dietitian to gain more insight into your diet, labs, and any recommended changes you may want to make.

Magnesium-Rich Foods for Kidney Patients

Fortunately, there are many foods rich in magnesium that kidney patients can enjoy.

Foods that have magnesium generally come with other nutrients like fiber, antioxidants, and potassium.

Table of Foods with Magnesium

Below is a table of magnesium-rich foods. We also included the amount of potassium for consideration for those with a potassium-restricted diet.

FoodServing SizeMagnesium (milligrams)Potassium (milligrams)
Pumpkin seeds1 ounce (28.35 grams)156223
Edamame (cooked)1 cup (155 grams)99675
Chia seeds1 ounce (28.35 grams)95115
Oat bran cereal (ready-to-eat)1 cup87230
Cashews1 ounce (28.35 grams)83187
Spinach (boiled)1/2 cup (90 grams)78839
Almonds1 ounce (28.35 grams)76208
Soymilk8 ounces (243 grams)61287
Black beans (cooked)½ cup (86 grams)60611
Peanut butter2 Tablespoons (32 grams)54238
Peanuts1 ounce (28.35 grams)48200
Brown rice, medium-grain, cooked½ cup43154
Russet Potato, baked1 small potato (138 grams)42759

Nutritional information obtained from the USDA Food Database.

Note that many of these foods are also high in potassium.

However, chia seeds, cashews, peanuts and brown rice all have 200 milligrams or less of potassium per serving.

These would be excellent high-magnesium foods that would still be acceptable for a low-potassium diet.

Magnesium in Mineral Waters

Some bottled mineral waters may be a good source of magnesium, containing more than 120 milligrams of magnesium per liter (18).

Bottled water may not list the amount of magnesium in milligrams. However, looking at the ingredients list may hint as to whether minerals like magnesium were added.

Magnesium in Tap Water

Some hard water may have up to almost 50 milligrams of magnesium per liter of tap water (19).

You can look at your local water reports or ask your water utility company for a water report to indicate the amount of magnesium in your water.

Are Magnesium Supplements Okay for Kidney Patients?

There are often situations in which a magnesium supplement could be helpful for kidney patients.

As discussed above, there are many situations where a kidney patient may benefit from a magnesium supplement

The first thing to do before taking any supplement is to discuss with your physician.

Your physician can order a magnesium test to determine if your magnesium levels are low and would benefit from a supplement.

On the other hand, your magnesium levels may be high enough where magnesium supplements would need to be avoided.

Either way, it is important to discuss with your primary care physician or nephrologist prior to starting any new supplement to ensure you have a solid plan in place.

Types of Magnesium Supplements

There are several different types of magnesium supplements. The different types can have a different purpose.

Purpose of Magnesium Supplements

As stated above, magnesium supplements can be used for low magnesium levels in the blood.

Additionally, magnesium supplements are often used to help treat:

  • Constipation
  • Type 2 diabetes
  • High blood pressure
  • Migraines (20)
  • Osteoporosis & bone health
  • Anxiety
  • Sleep

Best Magnesium Supplements for Low Magnesium Levels

Not all supplements are equally effective when it comes to replenishing low magnesium levels.

The best forms of magnesium for this purpose are:

  • Magnesium Lactate
  • Magnesium Chloride
  • Magnesium Glycinate
  • Magnesium Aspartate
  • Magnesium Orotate

Magnesium and Vitamin B6

You may often come across a magnesium supplement that also has vitamin B6.

This is because supplementing both magnesium and vitamin B6 (also known as pyridoxine) has been shown to help reduce stress levels and improve low magnesium levels (21).

Magnesium and Zinc

High doses of zinc may interfere with magnesium absorption.

Taking a zinc supplement of 142 milligrams per day reduced magnesium absorption in a study published in 1994 (22).

Be careful with any supplements that contain mega-doses as these may not only be unnecessary, but harmful for kidney patients.

Summary 

Magnesium is an important mineral for kidney patients. It can help reduce blood pressure, control blood sugars, and even protect kidney function.

It is found in fruits, vegetables, nuts, and seeds. Many kidney patients do not get enough magnesium in their diet due to restricting high-potassium foods that have magnesium. 

Lower-potassium foods rich in magnesium include peanuts, brown rice, chia seeds, and cashews. These can fit into a low potassium diet and provide more magnesium.

In some situations, a magnesium supplement is ordered by a physician. These can help restore low magnesium levels in the body. Magnesium supplements are also commonly used to treat conditions such as constipation, migraines, blood pressure, type 2 diabetes, osteoporosis, anxiety, and sleep.

However, kidney patients are at higher risk of high magnesium levels, so it is important that any supplement is approved by a physician and blood levels are consistently monitored to prevent high magnesium levels.

Registered Dietitian Nutritionist, Board-Certified Specialist in Renal Nutrition | Website |  + posts

Jen Hernandez is a registered dietitian and board-certified specialist in renal nutrition. She has nearly a decade of experience with kidney disease patients in all stages - from stage 1 through kidney transplant. Jen writes on the blog of Plant-Powered Kidneys to help reach and teach more kidney patients about how they can enjoy more foods in a plant-based diet while protecting kidney health.

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