Magnesium stearate is a white powder that combines the essential mineral magnesium and the saturated fat stearic acid. It provides a small amount of magnesium, but it's primarily used as an inactive ingredient in the pharmaceutical and supplement industries to produce pills with more consistent dosing.
Magnesium stearate provides a small amount of magnesium, as it consists of about 4 percent magnesium. You need magnesium for keeping your blood sugar and blood pressure at healthy levels, forming DNA and protein and keeping your muscles and nerves working properly. Women need at least 320 milligrams per day, and men need at least 420 milligrams per day for good health.
Use in Supplements
Manufacturers use magnesium stearate in some supplements and medications as an inactive ingredient to help keep the active ingredients flowing smoothly through the machinery used to produce the supplements. This is beneficial because it makes it more likely that each pill has a consistent dose of the active ingredients so each pill will have the same effect in your body.
Magnesium stearate is generally regarded as safe by the U.S. Food and Drug Administration. There are some rumors online that this inactive ingredient isn't safe, stating that it may suppress immune function and that it can form a biofilm and prevent the absorption of nutrients, based on preliminary animal studies.
An article published in Nutrition Review in November 2013 notes that these claims aren't valid, stating that magnesium stearate affected the immune function of mice because they lack an enzyme that converts stearic acid to oleic acid. That isn't a problem for people because we do have this enzyme. As for blocking the absorption of nutrients, the author notes that enzymes in your body break down stearic acid so it won't limit absorption.
If you want to avoid magnesium stearate, choose supplements in liquid or gummy form instead of tablet or capsule form. Although magnesium stearate is the most common lubricant used to make tablets, you can also find tablets made with alternative ingredients that serve the same purpose. These include substances called glycerine fatty acid esters, sodium behenate, sodium stearyl fumarate or stearic acid.