How Long Does Magnesium Citrate Stay in Your Body?

The amount of time magnesium citrate remains in your body can vary widely and depends on factors such as dose, formulation, and your body’s ability to absorb and eliminate magnesium.

How the Body Processes Magnesium

When you take magnesium citrate, your small intestine absorbs it quickly—within about an hour. Around 80% is absorbed in six hours. Your intestines, bones, and kidneys work together to tightly regulate magnesium levels. Roughly half of your body’s magnesium is stored in your bones, while the rest is found in muscles, soft tissues, and less than 1% in the blood. Excess magnesium is eliminated through urine.

Factors Affecting How Long Magnesium Citrate Stays in Your System

1. Your Magnesium Status  

If you are deficient in magnesium, your body will try to retain more of it by increasing absorption. Supplementing with magnesium citrate can help restore normal levels.

2. Form of Magnesium  

Different forms of magnesium are absorbed at different rates. Organic forms like magnesium citrate are more easily absorbed than inorganic forms like magnesium oxide. Magnesium citrate given for constipation works differently than supplements designed to raise magnesium levels.

3. Health Conditions  

Certain conditions can affect how your body handles magnesium:

- Vitamin D deficiency can reduce absorption.

- Diarrhea and vomiting can cause magnesium loss.

- Digestive diseases (such as celiac or Crohn’s disease) can reduce absorption due to frequent diarrhea.

- Diabetes can lead to more magnesium being excreted in urine.

- Alcohol use disorder can decrease magnesium through several mechanisms, including poor diet and digestive problems.

- Kidney disease can cause magnesium to accumulate because the body cannot eliminate it efficiently.

4. Dosage Amount  

How much magnesium citrate you take matters. Higher doses may lower the absorption rate, as the body is less efficient at absorbing large amounts at once. Smaller, more frequent doses are better absorbed than a single large dose. For example, 65% of a 36 mg dose was absorbed in one study, compared to only 11% from a 973 mg dose. Adult males need 400-420 mg of magnesium per day, while females need 310-320 mg. Intake of more than 350 mg of supplemental magnesium per day can cause side effects like diarrhea and cramps.

5. Medications  

Some medications can reduce magnesium absorption or increase loss. These include certain antibiotics, blood pressure medicines, diuretics, proton pump inhibitors, corticosteroids, estrogens, seizure medications, heart medicines, immunosuppressants, and stimulants.

6. Other Supplements  

High doses of some minerals, such as calcium, phosphorus, iron, copper, manganese, and zinc, can interfere with magnesium absorption and affect how much stays in your system.

7. Foods You Eat  

Certain foods may decrease absorption, such as those high in oxalates (spinach, cabbage, broccoli, Brussels sprouts) and phytates (bran, whole-meal bread), as well as certain fibers found in some grains, fruits, and vegetables. Diets high in sodium, calcium, caffeine, or alcohol can also promote magnesium loss through the kidneys.

8. Age  

Aging can reduce magnesium levels due to decreased intake, less efficient absorption, and increased loss through the kidneys.

In the United States, magnesium supplements are not regulated as strictly as prescription medications. Choose products tested by reputable organizations like NSF, U.S. Pharmacopeia, or ConsumerLab.com for quality assurance. For personalized guidance, consult your healthcare provider, registered dietitian, or pharmacist.