Stearic Acid: Function & Diseases

Stearic acid, along with palmitic acid, is a major component of fats and oils. It represents an unsaturated fatty acid with 18 carbon atoms, whose main function is to store energy. Since it can be synthesized in the organism, it does not need to be supplied as an essential part of the diet.

What is stearic acid?

Stearic acid and palmitic acid represent the two main components in vegetable oils and animal fats. In this context, stearic acid consists of 18 carbon atoms. It is therefore also known as octadecanoic acid. As with palmitic acid, its chemical structure is very simple. There is a carboxyl group at one end of the hydrocarbon chain with 17 carbon atoms. The carboxyl group provides the acid properties of the molecule. Due to the long hydrocarbon chain, the compound is almost insoluble in water. In free form, it is a white, tasteless solid that melts at 69 degrees and boils at 370 degrees. The salts of stearic acid are called stearates. Stearic acid and palmitic acid have similar chemical and physical properties. They differ only in the length of the hydrocarbon chain, which is only two carbon atoms shorter in palmitic acid. Both fatty acids also significantly determine the properties of triglycerides (fats and oils). While palmitic acid occurs in high concentrations in both animal and vegetable fats and oils, stearic acid is mainly found in animal fats. Vegetable oils usually contain only up to a maximum of 7 percent stearic acid. In addition to triglycerides, stearic acid is also present in cell membranes and nerve fibers. There it is present as a phospholipid or sphingolipid. Because of their chemical structure, which is similar to that of palmitic acid, the two fatty acids always occur in association. In animal or human organisms, stearic acid is produced from palmitic acid by the addition of two carbon atoms.

Function, effect, and tasks

The biochemical structure of stearic acid is not spectacular. Nevertheless, it possesses great physiological significance. As mentioned above, stearic acid represents a rather simply constructed hydrocarbon chain with a carboxyl group. In the organism, it serves as an effective energy store when bound to glycerol. When 100 grams of stearic acid are burned, about 900 kilocalories are released. This is almost twice the energy of the same amount of carbohydrates. The hydrocarbon bonds, which are present in large numbers in long-chain fatty acids, are particularly rich in energy. Because of this energy storage capacity, stearic acid and the other fatty acids are suitable as effective energy stores in the body. For this purpose, three fatty acids each are esterified with a glycerol molecule to form triglycerides or fats and oils. These triglycerides compress the energy-rich molecules again into a very small space, so that fats can function as one of the most energy-rich energy storage molecules. In evolution, organisms have evolved that have found a way to make provisions for bad times by storing fats and oils. Among other things, stearic acid and palmitic acid are also starting materials for the synthesis of the biologically more active unsaturated fatty acids. On their basis, in turn, many active substances such as prostaglandins can be formed. According to current findings, stearic acid alone does not have any major physiological effects. In addition to its function as an energy store, it is also a major component of phospholipids and sphingolipids, which in turn determine the structure of cell membranes and the membranes of cell organelles. The molecules consisting of hydrophilic and hydrophobic portions demarcate the cells from the intercellular area. The hydrophobic fatty acid chains protrude from the membrane towards the cytoplasm of the cell. At the same time, the hydrophilic portion of the cell points toward the cell surface. Recent research results indicate yet another physiological effect of stearic acid. By chance, scientists from the German Cancer Research Center discovered that stearic acid could have a controlling effect on mitochondria. Here, the stearic acid molecule acts as a signal transducer and leads to the fusion of mitochondria. As a result, mitochondrial function improves. Stearic acid could thus be used in the future to treat mitochondrial diseases.

Formation, occurrence, properties and optimal values

Stearic acid, like all other fatty acids, is synthesized by building a hydrocarbon chain through the stepwise addition of two carbon atoms at a time. Starting compounds are usually carbohydrates. However, the fatty acids and amino acids contained in food also serve as the basis for building up higher-chain fatty acids. Animal fats contain particularly high levels of stearic acid. Beef tallow, mutton fat, butterfat and lard are very rich in stearic acid. From a vegetable source, cocoa butter is the largest supplier of stearic acid. Other vegetable oils and fats usually only contain a maximum of 7 percent. Free stearic acid is produced by saponifying fats with boiling sodium hydroxide solution. This initially produces the sodium salt of the fatty acids, which are converted back into fatty acids by treatment with mineral acids. The subsequent separation of the individual fatty acids is carried out by special physical (distillation) or chemical processes. Stearic acid is used in cosmetic products, shaving foam, cleaning agents or detergents.

Diseases and disorders

Stearic acid does not exert any harmful effects under normal conditions. It is toxically neutral and well tolerated. However, fine dusts and vapors containing stearic acid can have corrosive effects. This results in local irritation, gastrointestinal problems and, in some cases, vomiting. If contact with these dusts and vapors is very intense, respiratory problems and pulmonary edema may occur. Magnesium stearate presents another problem. It is technically produced by hydrogenating palm oil, which is, however, contaminated with pesticides. Therefore, magnesium stearate used in dietary supplements can have toxic effects on the liver. In addition, skin damage and intestinal disorders may also be caused by the use of magnesium stearate.