Whether you’ve had customer inquiries or received e-mail alerts, there have been concerns raised regarding the safety of stearic acid and magnesium stearate in dietary supplements. Stearic acid is a saturated fatty acid found in many foods, including animal and vegetable fats and oils,1 and cocoa and flaxseed.2,3 Magnesium stearate is a magnesium salt of stearic acid—a compound containing two stearic acids and one magnesium.
In the body, stearic acid is primarily converted into oleic acid (a monounsaturated fatty acid).4 Oleic acid comprises the majority of olive oil, and may also be found in substantial quantities in grape seed oil, sea buckthorn oil and the açaí berry.5,6 In addition, oleic acid may be responsible for the blood pressure-reducing effects of olive oil.7 Consequently, even though stearic acid is a saturated fat, studies have suggested it has no negative effect on blood cholesterol levels since such a high proportion is converted to oleic acid.8 In fact, some research indicates stearic acid actually lowers low-density lipoprotein (LDL) cholesterol.9 After magnesium stearate is broken down into its component parts in the body, its fat is essentially the same as that of stearic acid, except the magnesium molecule supplies the body with this essential mineral.
Both compounds have become more commonly used in dietary supplements. Stearic acid is commonly used as a binder in tablets, and it has lubricant properties. Magnesium stearate is a lubricant commonly used in tablet formulations. After achieving a homogenous blend of powdered ingredients, adding a small amount of magnesium stearate enables the powder blend particle surface to be sufficiently coated while limiting penetration of the lubricant within the particle matrix.10 This allows tablets to be punched without sticking to the machinery, or capsules to glide shut easily and eject from the machinery.
The amounts of stearic acid and magnesium stearate typically used in a tablet are relatively minute. Stearic acid typically ranges between 0.5 and 10 percent of the tablet weight, while magnesium stearate typically represents 0.25 to 1.5 percent of the tablet weight.11 Therefore, in a 500 mg tablet, the amount of stearic acid would probably be about 25 mg, and magnesium stearate about 5 mg.