Can Magnesium Cause Diarrhea? A Registered Dietitian Nutritionist Explains

Magnesium is an essential mineral required for numerous reactions in your body, including blood sugar and blood pressure control, nerve and muscle function, and energy production.

Magnesium supplements fill the gap between average intake and the amount your body needs. However, magnesium can cause diarrhea. High doses of magnesium draw water into the gut, causing diarrhea or more than three loose or liquid bowel movements per day.

Magnesium and Diarrhea

You may be wondering, can magnesium cause diarrhea? The answer is yes. The following explains how.

Most magnesium supplements are salts, meaning magnesium is bound to another molecule to help with absorption. However, when the body does not absorb magnesium salts, they can draw in water and increase bowel movements. 

Magnesium is mainly absorbed in the small intestine. However, some absorption also occurs in the colon. How much magnesium is absorbed may depend on the type and amount of magnesium you consume. Smaller doses may be better absorbed than larger doses. 

The tolerable upper intake level (UL) for magnesium—350 milligrams daily for adults—is the maximum amount unlikely to cause side effects. This limit generally applies to supplements and medications, as it may be unlikely that it would be reached from food sources alone.

Supplements provide high doses of magnesium at one time, which can lead to excessive unabsorbed magnesium. When magnesium is poorly absorbed or not absorbed, it causes loose stools or diarrhea. 

Types of Magnesium More Likely to Cause Diarrhea

Although all types of magnesium can cause diarrhea, some are more likely than others. The body absorbs magnesium differently depending on the form consumed. When magnesium is not well absorbed, it causes loose stools and diarrhea.

Types of magnesium that are poorly absorbed and more likely to cause diarrhea include the following: 

• Magnesium citrate: This form treats constipation, increasing the number of bowel movements. Magnesium citrate is considered a saline laxative. Saline laxatives contain salt to help draw water into the stool, making it easier to pass. Additionally, because of how well magnesium citrate dissolves, it may be more likely to cause diarrhea. 
• Magnesium oxide: This form acts as an antacid to help with heartburn or indigestion. Magnesium oxide is also used as a laxative for short-term, rapid bowel emptying, often before surgery or a medical procedure like a colonoscopy.
• Magnesium hydroxide: Like magnesium citrate, magnesium hydroxide is a saline laxative used to temporarily treat constipation. Bowel movements occur 30 minutes to six hours after taking magnesium hydroxide. 
• Magnesium carbonate: This type is less commonly used because it is not as well dissolved or absorbed in the body. 
• Magnesium sulfate: This supplement empties the large intestine and bowel before a colonoscopy. It is also an osmotic laxative. Osmotic laxatives draw water into the colon to soften stool and produce watery diarrhea. Unlike saline laxatives, osmotic laxatives do not contain salt. Magnesium sulfate also has topical uses. Epsom salts contain magnesium sulfate.
• Magnesium chloride: This form is available as an oral supplement, topical ointments, and injectable formulas. Additionally, it is a common ingredient in household cleaning supplies.  

Even though they’re more likely to cause diarrhea, magnesium citrate, and magnesium oxide are among the most commonly prescribed magnesium supplements.

What Types of Magnesium Do Not Cause Diarrhea?

All types of magnesium can cause diarrhea. However, some are less likely to cause diarrhea than others. When magnesium is better absorbed by the body, fewer gastrointestinal (GI) issues like diarrhea occur.

Some types of magnesium that may cause less diarrhea include the following:

• Magnesium gluconate: This type is prescribed for low blood magnesium, often due to gastrointestinal issues or prolonged vomiting or diarrhea. Magnesium gluconate is a more common supplement because it is less likely to cause diarrhea.
• Magnesium glycinate: This form helps resolve magnesium deficiency. It combines the protein (amino acid) glycine with magnesium. Magnesium glycinate is often recommended to help with sleep, as glycine and magnesium affect neurotransmitters that promote relaxation. Still, additional research is needed to understand magnesium glycinate’s role in sleep fully.
• Magnesium lactate: This form of magnesium is a food additive in yogurts and fruit-flavored beverages, where it is a source of dietary magnesium.
• Magnesium L-threonate: This particular supplement contains the L-threonate form of magnesium, which may boost cognition and benefit symptoms of attention deficit hyperactivity disorder (ADHD). Still, additional research is necessary, given that the studies were small and used high doses of magnesium L-threonate (greater than 2 grams daily).
• Magnesium malate: This type is formed by combining magnesium and malic acid. It dissolves well in the body and is highly bioavailable. Malic acid is a weak organic compound found in fruits and vegetables.

What Are the Signs of Too Much Magnesium?

It is difficult to consume too much magnesium via diet alone. Instead, too much magnesium is more likely to be found in high-dose supplements. Signs of too much magnesium may include the following:

Symptoms of dangerously excessive magnesium (hypermagnesemia) include the following:

Contact your healthcare provider if you experience any of the symptoms of too much magnesium.

Hypermagnesemia is rare but potentially life-threatening, typically affecting those with impaired kidney function or those taking high-dose magnesium supplements or infusions.

How Much Magnesium Do I Need Each Day?

The recommended dietary allowance (RDA) is the average daily amount of magnesium required to meet the nutrient needs of nearly all healthy individuals.

The RDA for magnesium is the following:

• Females 31 and older: 320 mg
• Females 19 to 30: 310 mg
• Males 31 and older: 420 mg 
• Males 19 to 30: 400 mg

Most Americans do not consume enough magnesium, and certainly not from dietary sources alone. Since most people do not meet daily recommendations, you can take a magnesium supplement daily to ensure you reach the RDA.

What Foods Are High in Magnesium?

Magnesium is found in many plant-based foods, including nuts, seeds, and legumes (peas, beans, and lentils). Grains and cereal products are often fortified with magnesium to help meet recommended intakes. 

Common sources of magnesium include the following:

• Pumpkin seeds: A 3.5-ounce (nearly one-half cup) serving contains 500 mg of magnesium.
• Almonds: A 3.5-ounce serving of raw almonds contains 260 mg of magnesium.
• Spinach: A 1-cup serving of boiled spinach has 160 mg of magnesium.
• Edamame: A one-half-cup serving has 100 mg of magnesium.
• 2% milk: A 1-cup serving of 2% milk contains 30 mg of magnesium.
• Cashews: A 3.5-ounce serving of raw cashews contains 250 mg of magnesium.

Adding a magnesium supplement helps ensure you meet nutrient recommendations. Various magnesium forms and doses exist, so you can pick the type that works best for you to add to the magnesium you get from food.

Supplements That Increase Magnesium Absorption

Taking magnesium with other supplements can influence how it is absorbed in your body. 

Other supplements or nutrients can influence magnesium absorption:

• Calcium and vitamin D: Both support bone health and may affect magnesium absorption, though more research is needed. Maintaining adequate vitamin D and calcium levels is vital for optimal magnesium absorption.
• Protein: Higher protein intake may improve magnesium absorption by preventing binding with calcium and phosphate.
• Zinc: Essential for health and may enhance magnesium absorption, but avoid exceeding the tolerable upper limit to prevent adverse effects.

Managing and Preventing Diarrhea from Magnesium Supplements

When taking magnesium supplements, consider the following steps:

• Start small and slow: Begin with a low dose and gradually increase it to the recommended amount.
• Spread out your dosage: Taking smaller doses throughout the day may decrease side effects like diarrhea.
• Take with food: This may help minimize the risk of diarrhea.
• Try different forms: If you experience diarrhea, consider switching to a different type or form of magnesium.
• Stay hydrated: Drink fluids and consider electrolyte solutions to keep hydrated if you have diarrhea.
• Consult your healthcare provider: Get in touch with a provider if diarrhea persists or worsens.
• Consider higher magnesium foods: Getting magnesium from food typically poses a lower risk of overdose and may enhance absorption due to other nutrients.

Summary

All magnesium supplements can cause diarrhea, but some forms of magnesium may be less likely to cause it. If you supplement with magnesium, start with a small dose and take it with food to reduce the chance of diarrhea. Consult a healthcare provider before starting a new supplement to ensure it will be safe and effective for you.