Linoleic acid

Linoleic acid (LA) is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2(n-6). Chemically, linoleic acid is a carboxylic acid with an 18-carbon chain and two cis double bonds; the first double bond is located at the sixth carbon from the methyl end.

Linoleic acid belongs to one of the two families of essential fatty acids that humans and animals must ingest for good health, because the body requires them for various biological processes, but cannot synthesize them from other food components.

The word "linoleic" comes from the Greek word linon (flax). Oleic means "of, relating to, or derived from oil or olive" or "of or relating to oleic acid" because saturating the n-6 double bond produces oleic acid.

In physiology
LA is a polyunsaturated fatty acid used in the biosynthesis of arachidonic acid (AA) and thus some prostaglandins. It is found in the lipids of cell membranes. It is abundant in many vegetable oils, comprising over half (by weight) of poppy seed, safflower, sunflower, and corn oils.

Linoleic acid is an essential fatty acid that must be consumed for proper health. A lack of LA and other n-6 fatty acids in the diet causes dry hair, hair loss, and poor wound healing. However, achieving a deficiency in linoleic acid is nearly impossible consuming any normal diet and is thus not considered to be of clinical concern.

Along with oleic acid, linoleic acid is released by cockroaches upon death to deter other roaches from entering the area. This is similar to the mechanism found in ants and bees, in which oleic acid is released upon death.

Metabolism and eicosanoids


The first step in the metabolism of LA is performed by Δ6desaturase, which converts LA into gamma-linolenic acid (GLA).

There is evidence suggesting that infants lack Δ6desaturase of their own, and must acquire it through breast milk. Studies show that breast-milk fed babies have higher concentrations of GLA than formula-fed babies, while formula-fed babies have elevated concentrations of LA.

GLA is converted to Dihomo-gamma-linolenic acid (DGLA), which in turn is converted to arachidonic acid (AA). One of the possible fates of AA is to be transformed into a group of metabolites called eicosanoids, a class of paracrine hormones. The three types of eicosanoids are prostaglandins, thromboxanes, and leukotrienes. Eicosanoids produced from AA tend to be inflammatory. For example, both AA-derived thrombaxane and leukotrieneB4 are proaggretory and vasoconstrictive eicosanoids. The oxidized metabolic products of linolenic acid, such as 9-hydroxyoctadecanoic acid and 13-hydroxyoctadecanoic acid, have also been shown to activate TRPV1, the capsaicin receptor, and through this might play a major role in hyperalgesia and allodynia.

An increased intake of certain n–3 fatty acids with a decrease in n-6 fatty acids has been shown to attenuate inflammation due to reduced production of these eicosanoids.

One study monitoring two groups of survivors of myocardial infarction concluded “the concentration of alpha-linolenic acid was increased by 68%, in the experimental group, and that of linoleic acid reduced by 7%...the survivors of a first myocardial infarction, assigned to a Mediterranean alpha-linolenic acid rich diet, had a markedly reduced rate of recurrence, other cardiac events and overall mortality.”

Industrial uses
Linoleic acid is used in making quick-drying oils, which are useful in oil paints and varnishes. These applications exploit the easy reaction of the linoleic acid with oxygen in air, which leads to crosslinking and formation of a stable film.

Reduction of linoleic acid yields linoleyl alcohol.

Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's anti-inflammatory, acne reductive, and moisture retentive properties when applied topically on the skin.