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Is magnesium stearate safe? -- woman looking at ingredients on supplement label


The first thing to understand is that magnesium stearate is added to supplements not for any nutritional benefit, but because it creates an even distribution of active ingredients and prevents ingredients and tablets from sticking to machines during production. It is created from reacting stearate (from animals or plants) with magnesium. A very small amount is used in supplements, and it typically comprises less than 1% of a total formulation. If it's in a product, you'll see it included in the "Other Ingredients" section of supplement labels.  

One popular website claims that magnesium stearate can promote the growth of bacterial colonies in the gastrointestinal tract and create a "biofilm" preventing the absorption of nutrients. However, there does not seem to be clinical evidence behind this.  In fact, a laboratory study (Soni,  J Food Prot 2008) found stearic acid to inhibit the formation of biofilms.

The claim that magnesium stearate (which is the magnesium salt of stearic acid) suppresses the immune system seems to be based on effects seen with stearic acid. For example, laboratory studies on immune cells from mice found that large amounts of stearic acid will damage the cell membranes of T-lymphocytes (Tebbey, Immunology 1990).  However, these laboratory conditions do not represent what happens inside your body when you ingest normal amounts of stearic acid, let alone very small amounts of magnesium stearate.  It is highly unlikely the small amount of magnesium stearate in supplements cause immune suppression and such an effect has not been reported.

Concern has also been raised about the stearic acid in magnesium stearate raising cholesterol levels, as it is a saturated fat.  This should not be a concern because even normal dietary intake of stearic acid has been shown to have no significant effect on total cholesterol, LDL or HDL cholesterol levels (Yu, Am J Clin Nutr 1995).  In addition, the amount of stearic acid from magnesium stearate in supplements is very small.  According to USDA nutrition surveys, the average American adult consumes between 5,900 to 8,800 milligrams of stearic acid each day, typically from food sources like beef, poultry, cocoa butter, milk and cheese.  A single chocolate bar contains about 5,000 milligrams of stearic acid.  Meanwhile, the amount of stearic acid in the magnesium stearate in a dietary supplement is generally less than 20 milligrams.

The bottom line
There does not appear to be a safety concern with magnesium stearate from dietary supplements.  At the same time, there is no nutritional advantage to having it in your supplement, although it allows manufacturers to provide a more consistent product. If you want to avoid it, check the list of "Other Ingredients" in Supplement Facts panels of products and choose one without it. ConsumerLab.com publishes all of the listed ingredients for every product in its Reviews -- just click on "Ingredients" under the name of any product in the results table of any report.  You should also be aware that the magnesium stearate used in dietary supplements can be manufactured from vegetable or animal sources. If you're looking for a vegetarian source, look for a product that lists "vegetable grade" or "vegetable magnesium stearate." Otherwise, it is most likely sourced from animals.
For information about other inactive ingredients used in supplements, see ConsumerLab.com's Review of Inactive Ingredients.

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January 25, 2016

Wonderful information , i have always not known why it was added , without really caring , but with this information i feel very comfortable if it is one of the added ingredients to my supplements

August 1, 2018

Just to clarify, magnesium stearate is NOT natural-- it does not occur anywhere in nature. It is produced by a high heat process that combines magnesium with stearic acid. Having worked in health food stores for over 20 years, I have heard enough people tell me that magnesium stearate causes them to have headaches, and their headaches went away after they stopped taking supplements that had mag stearate in them. My concern would be what effect does mag stearate have on your cells. How does it prevent material from adhering to the tabletting or encapsulation machinery? Why wouldn't it affect your cell membranes the same way? Personally, I stay away from it. There are other "cleaner" supplements available.

Michael K16507
February 25, 2018

Thank you for providing an answer to a point of consumer confusion generated by negative sales tactics that have been corrected by at least a half dozen quality manufacturers.

In fact, one study by tablet chemists Vitkova and Chalabala described magnesium stearate as the best tablet lubricant because of all the things that you said, AND that other flow agents can cause higher manufacturing costs, while not performing well to allow tablet disintegration to be adequately predictable.

I have a review that included statements confirming that magnesium stearate is the
"lubricant of choice" from a number of science-based companies, scientists and long-term researchers, including Nutricology, Jarrow Formulas, Chris Kresser, Nutri-Spec, ConsumerLabs and Dana Dana Myatt, NMD in the Nutricology Newsletter, In Focus, April 2003.

July 24, 2017

Can magnesium stearate cause diarrhea?

July 24, 2017

Hi Joe -- Diarrhea is not a known side effect of magnesium stearate in the amounts typically used in supplements.

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