The Betterment Project

What Is Magnesium Stearate & Is It Safe?

The scenario is all too common: You buy a new product or supplement, you turn it over to read all the directions closely and carefully — then your eyes start to glaze over as you get to the active and inactive ingredients list. 


Some words look familiar, some you can’t pronounce. 


At the end of the day, all the questions boil down to one: Is this safe? Magnesium stearate is one of those ingredients that makes the list in many nutritional supplements and care products. 


Magnesium certainly looks familiar, but what is stearate? 

It’s time to dive into those burning questions:


  1. What is magnesium stearate exactly? 


  1. Is magnesium stearate safe to use?

Magnesium and Stearic Acid

As stated, magnesium stearate is found in many nutritional supplements. However, it actually refers to a combination of two nutritional substances: Magnesium and stearic acid. Together they form a simple salt.


Let’s take a moment to look at each more closely before we look at their combination.


Magnesium, The Trace Mineral


Magnesium is a naturally occurring trace mineral found in many of the foods we eat. Its value to our health cannot be overstated, it is an essential element. 


As a dietary trace mineral, magnesium plays a versatile role. Its main function lies in enzyme reaction. It interacts with over 300 enzymes in the body and facilitates and supports many key systems like metabolism, nerve and muscle function, and protein synthesis.


The average adult has about 25 g of magnesium in their body; stored mostly in the skeletal systems and soft tissue. 


Food and Supplementation


Magnesium, as a dietary mineral, is consumed through many foods: Leafy greens, fruits, fish, seeds, and legumes, to name but a few. 


It is also consumed as a standalone supplement — common forms being magnesium citrate, aspartate, glycinate, and oxide — and in combination with other daily supplements.


The uses and benefits for magnesium supplementation are many. Some use it because of dietary deficiencies, others for things like sleep health


Stearic Acid, The Fatty Acid

The stearate portion of magnesium stearate refers to stearic acid; also referred to as octadecanoic acid. It is one of the most common long-chain fatty acids naturally occurring in all humans, animals, and plants. 


Fatty acids, of course, are the building blocks of fats and lipids. They are identified and classified by the carbon atoms attached to them, which can be numerous — hence, long-chain. 


Not to get too far into the chemistry weeds, but stearic acid is an 18-carbon chain fatty acid. It is one of the most predominant saturated fats in the human diet — we consume several thousand milligrams each day through animal and vegetable fats. 


Stearic Acid as a Natural Ingredient


Dietary stearic acid is important to our body, studies have shown it has a role to play, especially in cardiovascular function. But it has also found uses as a naturally-derived ingredient. 


Stearic acid is used in many personal care products, especially natural skin care products. Its main uses are to facilitate other skincare ingredients; acting as a surface agent, lubricant, and emollient in many moisturizers, lotions, and cleansers. 


It is also used as a natural emulsifier; helping bind ingredients and preventing them from separating. In supplements, this role as a natural emulsifier is where it is most often seen in combination as magnesium stearate.

Magnesium Stearate

Now it is time to look at the combination of these two substances, derived as magnesium stearate. 


Essentially, magnesium stearate is a simple salt derived from the two substances discussed above. In chemistry terms, magnesium stearate is formed when a magnesium ion molecule bonds with two stearic acid anion molecules. 


It is widely used as an inactive ingredient and excipient in supplement manufacturing; mostly in medication and supplement capsules. It is known as being a flow agent.

Magnesium Stearate as a Flow Agent

Excipients are widely used in the supplement industry. Natural, non-toxic excipients help maintain the integrity of the supplements within the capsules. Normally, they do not contribute to any sort of nutritional benefit. 


Magnesium stearate is used as a powdered excipient or what is sometimes referred to as a flow agent. Flow agents act as lubricants and anti-caking agents. 


In short, flow agents help keep dosing consistent during the manufacturing process — helping keep ingredients from sticking to one another and to encapsulating equipment.  


Magnesium Stearate as a Release Agent


According to the Food and Drug Administration, magnesium stearate is also used as a release agent, helping to enhance and promote the absorption, solubility, and therapeutic effect of other active ingredients. 

Is Magnesium Stearate Safe?

The question remains: Is magnesium stearate safe? Let’s explore the question a bit closer. 


The safety and use of magnesium stearate has been a contentious discussion, but we must let the facts bear out its safety and efficacy. Here are a few of the main concerns charged against magnesium stearate.


Effect on Some Immunity Cells

The most popular claim leveled against magnesium stearate is that it suppresses immune cell function, specifically T-cells. To date, there is only one study from 1990 that makes the claim. 


Scientists performed the research on mice. They isolated the rodent T-cells, incubated them, and “soaked” them in stearic acid. The T-cell membrane was compromised, causing the cells to lose their function. 


The study, however, did not actually employ magnesium stearate. The findings remain questionable because of the nature of the experiment and the fact that it didn’t address stearic acid in dietary use, but simply bathed the cells in it. 


To date, the study has never been repeated.

Pesticide and Contamination Concerns


Some other concerns have to do with how magnesium stearate is derived and the manufacturing processes. In most cases, magnesium stearate is derived from plant oils; e.g. cottonseed oil. 


Concerns have been raised about the potential for contamination by pesticides. However, since magnesium stearate is a highly purified substance there is sparse evidence to support the claim. 


Other concerns have to do with manufacturing practices. Most claims point to one incident reported by the World Health Organization in 2011 in which some batches of the substance were contaminated with potentially harmful chemicals. 


However, the incident was isolated and no further concerns have been published since. 

The Bottom Line on the Safety of Magnesium Stearate


So, can magnesium stearate be consumed safely? Yes. 


As an additive and excipient in food and supplements, magnesium stearate is approved by the FDA. Stearic acid alone is consumed daily in many food sources; 7,000 mg on average.


According to the National Center for Biotechnology Information a safe amount of magnesium stearate for human consumption is 2,500 mg per kilogram of body weight per day. That’s roughly 182,500 mg for an adult weighing 160 pounds. 


The good news is, supplement manufacturers that employ magnesium stearate as a flow or release agent use only a fraction of the amount deemed as safe. 


You would need to consume a garbage bag full of magnesium stearate-containing supplements to even reach the safe amount threshold.


Final Thoughts

Magnesium stearate makes a helpful ingredient as a flow and release agent in the supplement industry. 

These industries use it in safe, minuscule amounts that stay well below the safe amount threshold.


Of course, if safety is still a concern it never hurts to consult your physician. 


Dietary stearic acid regulates mitochondria in vivo in humans | NCBI

CFR - Code of Federal Regulations Title 21 | FDA

Molecular basis for the immunosuppressive action of stearic acid on T cells | NCBI

Contaminated magnesium stearate excipient in finished products | WHO

Magnesium stearate | NCBI

Meet our Experts

This article has been reviewed by members of our Scientific Advisory Board.

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