Magnesium citrate and magnesium carbonate are two forms of the mineral commonly used in dietary supplements.
Neither one is the absolute best absorbed magnesium form, but the citrate preparation is a superior formula with a 10% higher absorption rate compared to carbonate. T
his significant difference in bioavailability between the two preparations is one of the main reasons why the citrate form is preferred as a dietary supplement for correcting a magnesium deficiency and associated symptoms.
Bioavailability of magnesium salts (a fancy, more scientific name for the different forms of magnesium in dietary supplements) is impacted by a number of factors.
Taking the essential mineral with vitamin D, for example, can potentially increase its bioavailability and uptake.
But taking it with a high dose of calcium can have the adverse effect, reducing bioavailability of the magnesium and consequently also how much of it your absorb.
Other essential nutrients such as phosphorus or copper, iron or manganese or zinc compete for absorption, potentially reducing magnesium uptake. Antibiotics, antacids, other medication or even some herb-based products as well as alcohol or excessive intake of coffee, caffeinated beverages or caffeinated tea can reduce absorption of the mineral.
On the bright side, a more severe the deficiency can result in increased uptake of the mineral. Essentially, the more deficient you are in magnesium, the more of the mineral your are likely to absorb, even from a supplement form with an otherwise poor bioavailability.
Just as interesting, a medical condition, increased intellectual and physical demands and stress all eat up magnesium reserves in the body and may, in turn, not only create demands for more of the mineral (which is drawn from bones if diet doesn’t supply adequate amounts), but may potentially also add up to an increased uptake from dietary supplements.
Mg citrate versus carbonate bioavailability
Magnesium citrate bioavailability can be as high as 30%, whereas magnesium carbonate bioavailability can be as high as 20%.
In some instances, the carbonate form has been found to have a maximum absorption rate of less than 10%.
So, of the two, the most bioavailable magnesium form is citrate, meaning you are likely to get more magnesium from this formula than from the carbonate formula.
Of course, bioavailability is affected by a number of factors, not just the form in which the mineral comes.
But it is one of the most important factors. In dietary supplements magnesium is bound to another compound, a salt of an acid or amino acid.
This other compound has a direct and important impact on the bioavailability of the mineral.
In the citrate form, magnesium is bound to citric acid, an organic acid naturally found in citrus fruits, especially lemons and limes, but also in yuzu, ugli fruit or oranges.
In the magnesium carbonate formula, the mineral is bound to a salt of carbonic acid. Of the two, the magnesium citrate formula is more soluble in water and more readily absorbed than the carbonate formula which contributes to its higher bioavailability.
Frequently asked questions
Why is citrate the most bioavailable magnesium of the two forms?
This particular form of the mineral is more soluble in water which helps with its absorption. By comparison, magnesium carbonate is a formula less soluble in water which leaves it to the stomach acid to process it for optimal absorption.
But existing malabsorption problems, having too little stomach acid, taking antacids or proton-pump inhibitors for acid reflux disease or gastritis treatment can inadvertently also affect magnesium absorption.
Is magnesium carbonate any good?
Yes, it is. Some people respond well to this form of the mineral and can enjoy benefits as a result of supplementation. I am one example of such a person. I have taken powder magnesium carbonate doses of 150 mg and 300 mg and can honestly say I have experienced great results with this formula.
For one, the effects were almost immediate, a matter of minutes. I found it to be a great formula and dose for anxiety and calming nerves, reducing stress and lowering a rapid heart rate. Over the course of a few days of supplementation, I have noticed benefits for muscle cramps and spasms too.
Even though it has a poorer solubility in water compared to citrate and has, in the best of cases, a 20% absorption rate. In the worst of cases, it has an absorption rate of up to 10%. Even so, it’s better than magnesium oxide whose absorption rate is often as low as 4%. It can be just as good for you as other forms with higher bioavailability ratings.
Uses and side effects of the magnesium forms
What does magnesium citrate do?
The most important uses of this form of the mineral include correcting a magnesium deficiency, relieving heartburn from acid reflux and treating constipation.
Other reasons for taking magnesium citrate include improved sleep, reduced anxiety and stress, fewer muscle cramps and spasms, stronger bones, benefits for the cardiovascular system, for blood sugar control in type 2 diabetes and for pregnant women. Available options include capsules, tablets, oral solution and powder formulation.
The most common side effects of magnesium citrate are diarrhea and associated abdominal cramps and a potential electrolyte imbalance.
Dosage is established according to the reason for taking it and age. As an adult, when taking magnesium citrate, remember to drink plenty of water, as instructed on the package.
If it’s for constipation relief, expect to have a bowel movement in up to 4-6 hours. If it’s to correct a deficiency, a good tip is to split your dose in two, half in the morning and half in the evening, to ensure you are getting a steady supply of the mineral throughout the day and night. It helps to eat before if you are looking to avoid stomach upset.
What does magnesium carbonate do?
Magnesium carbonate uses include correcting a deficiency, relieving heartburn, indigestion (dyspepsia) and constipation.
There are also benefits for muscles, bones, the nervous and cardiovascular system, blood sugar control and mental health.
Dosage is established according to the purpose for which the mineral preparation is used. In adults, doses of up to 350 g of magnesium carbonate powder are meant for correcting a deficiency, whereas doses of up 40 ml a day (liquid form) are meat for relieving heartburn and indigestion.
A high dose of magnesium carbonate can cause diarrhea and side effects such as abdominal cramps and bloating. Side effects are usually mild.
Important: In rare cases, allergic reactions to magnesium may occur. Seek medical assistance if you experience red, itchy skin, blisters, swelling of the lips, tongue or throat, difficulty breathing, wheezing, hoarseness, low blood pressure, dizziness, fainting, nausea or vomiting.