Magnesium Stearate

Magnesium Stearate

Like most vitamin companies, Nutristart uses magnesium stearate in the production of our supplements. More and more we are hearing from those critical of magnesium stearate, so I thought I would address this issue in a newsletter.

Why is Magnesium Stearate Used in Supplements?

Magnesium stearate is used in the production of most tablets, and capsules, for dietary supplements, and pharmaceutical drugs. It is also found in some cosmetics, and many food products, including candies, spices, and baking ingredients.

Magnesium stearate is used as an inert flow agent for the purposes of blending ingredients. Its use ensures that doses of ingredients are consistent in each pill. It is also required to ensure the encapsulation machines run smoothly, by serving as a lubricant, preventing ingredients from sticking to manufacturing equipment.

What is Magnesium Stearate?

Magnesium stearate is technically a magnesium salt produced by attaching magnesium to two stearic acid molecules.

Stearic acid is a long-chain, saturated fatty acid found commonly in foods, and abundantly in beef, cocoa butter, and coconut oil. Even though it is a saturated fat, it does not elevate cholesterol levels, and has never been shown to increase the risk of heart disease.

Now, people ingest far more stearic acid from foods than they could ever get even from copious amounts of supplements. For example a chocolate bar can contain up to 5 grams of stearic acid, whereas a capsule might contain around 10 mg.

From the perspective of manufacturing pills, magnesium stearate, being made from plant fats, is a vegetarian option to lab produced stearic acid. Stearic acid is what pharmaceutical companies use to produce drugs (including over the counter drugs). But, since commercial stearic acid is made from animal fat (beef or pork), the health food industry moved towards magnesium stearate, given the amount of vegetarians in their customer base. (The little known fact that stearic acid is usually made from pork makes me wonder how those who don’t eat pork for moral/political/religious reasons would feel if they knew that a simple over the counter pain reliever could contain pork ingredients.)

Why are People Concerned?

Online critics of magnesium stearate claim that it negatively affects the immune system, and inhibits the absorption of supplements. Others claim it causes a range of symptoms including joint pain, nausea, and even neurological problems.

The primary study referred to when accusing magnesium stearate of affecting the immune system is one titled, “Molecular basis for the immunosuppressive action of stearic acid on T cells.”  (Study)

In this experiment, immune cells from mice were saturated in a solution containing stearic acid (with a few other substances), which resulted in their T cells incorporating the stearic acid into the cell membrane. This destabilized the membrane so much that it caused the cell to die.

So, firstly, the study used stearic acid not magnesium stearate. Next, our cells are not bathed in stearic acid, it is consumed as part of the diet (or from pills), and goes through the digestive tract. And, lastly, we are not mice. Mice lack the ability to desaturate fatty acids, unlike humans, who easily desaturate fatty acids. Thus, even if our cells were bathed in stearic acid, it would not affect the membrane function.

Now let’s look at the idea that magnesium stearate inhibits nutrient absorption.

This criticism is based on a laboratory study which found that tablets made with magnesium stearate dissolved slower than tablets without magnesium stearate (in an artificial medium mimicking gastric fluids). Again, a study that does not use an actual human digestive system.

And, another study found that magnesium stearate didn’t affect tablet dissolution at all. (Study)

As well, another previous study concluded that, while magnesium stearate increased the time it took for a drug to dissolve, it had zero effect on the overall bioavailability of the drug (based on blood tests of the subjects).  (Study)

The argument that magnesium stearate inhibits nutrient (or drug) absorption is often supported by the claim that it will form biofilms in the intestinal tract. (“A biofilm is a consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances.” Wikipedia)

Biofilm both coats the intestinal tract, reducing nutrient absorption, and protects pathogenic bacteria from being destroyed by the body, leading to ailments like SIBO (small intestine bacterial overgrowth).

This thesis is based on the idea that soap scum (which forms a film on the bathtub or shower) is composed of magnesium and calcium stearate, and therefore magnesium stearate can create a film on your intestines.

Clearly the intestinal tract is a far different environment from an inert shower door, and there are no studies even implying that magnesium stearate can create a film on human intestines.

Is Magnesium Stearate Safe? 

According to the FDA, magnesium stearate is generally considered safe for human consumption at levels below 2500 mg/kg per day. This is an amount so much larger than any amount encountered through supplement use, that it becomes a non-issue. (Reference)

Humans ingest large amounts of stearic acid from foods, and our liver converts stearates and stearic acid into oleic acid. Oleic acid is a monounsaturated fat, found in avocado and olive oils, and is generally good for human health. Yet another indication of its safety.

Finally, in a laboratory study designed to test the safety of magnesium stearate, cultured cells were examined to determine its potential to induce genetic toxicity. The conclusion was, “These data indicate a lack of genotoxic risk posed by magnesium stearate consumed at current estimated dietary exposures.”  (Study)

Some People are Allergic to Magnesium Stearate

Now, there is no escaping the anecdotal feedback from many people who find their health improves when they avoid products containing magnesium stearate. Adverse responses include asthma, joint pain, panic attacks, and other symptoms as well.

One woman who developed hives, and pins and needles sensations in her face and joints, ultimately was diagnosed with a hypersensitivity to magnesium stearate.

Another testimonial involved a fellow who “was going along ok having cut out magnesium stearate from my life, and then suddenly I got the exact same reaction…….to eggs”. Eggs are a source of stearic acid, thus revealing him to be allergic to all stearates, not just magnesium stearate.

Magnesium stearate is commonly put on avoid lists for those with sensitivity to the nightshades (bell peppers, eggplant, potatoes, tomatoes). Therefore, those with nightshade allergies should also watch for a reaction to products containing magnesium stearate.

Though rare, those suffering from “alpha gal” meat allergy cannot tolerate food, or supplements, that contain stearates derived from animal fats. And they may indeed also react to magnesium stearate from vegetable sources, given its chemical similarity to stearic acid.

(“Alpha-gal syndrome is a recently identified type of food allergy to red meat. In the United States, the condition most often begins when a Lone Star tick bite transmits a sugar molecule called alpha-gal into the body.” Mayo Clinic)

While it is good that those who experience a reaction to the stearates share this information, potentially helping others with a similar response, it does appear that they are a minority. Just because a small portion of the population has an allergic response does not mean that it is an issue for the general population. Certainly if you believe you may have such an allergy it is worth discontinuing using supplements that contain magnesium stearate for a month or so, to see if your symptoms resolve.


Magnesium stearate (and stearic acid) are used in the formulation of tablets and capsules because, over the decades, they have proven to be the most cost effective, best tablet lubricant, one that allows for predictable tablet disintegration.

Magnesium stearate use is supported by respected nutritional authorities such as Chris Kresser, ConsumerLabs, and Dr. Dana Myatt. It is used by the vast majority of supplement producers including the stalwarts Jarrow Formulas, Life Extension Foundation, and Nutricology.

As with most of modern life, choices must be made based on a risk versus benefit ratio. I take large amounts of supplements (and have done so for decades), and I am comfortable that the benefits I garner far outweigh any risk that a small amount of magnesium stearate might cause.

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