Taurine, or 2-aminoethanesulfonic acid, is an organic acid. It is also a major constituent of bile and can be found in the lower intestine and amounts in the tissues of many animals and in humans as well. Taurine is a derivative of the sulfur-containing (sulfhydryl) amino acid, cysteine. Taurine is the only known naturally occurring sulfonic acid.

Taurine is named after the Latin taurus, which means bull or ox, as it was first isolated from ox bile in 1827 by German scientists Friedrich Tiedemann and Leopold Gmelin. It is often called an amino acid, even in scientific literature, but as it lacks a carboxyl group it is not strictly an amino acid. It does contain a sulfonate group and may be called an amino sulfonic acid. Small polypeptides have been identified which contain taurine but to date no aminoacyl tRNA synthetase has been identified as specifically recognizing taurine and capable of incorporating it onto a tRNA.

The major pathway for mammalian taurine synthesis occurs in the liver via the cysteine sulfinic acid pathway. In this pathway, the sulfhydryl group of cysteine is first oxidized to cysteine sulfinic acid by the enzyme cysteine dioxygenase. Cysteine sulfinic acid, in turn, is decarboxylated by sulfinoalanine decarboxylase to form hypotaurine. It is unclear whether hypotaurine is then spontaneously or enzymatically oxidized to yield taurine.

Taurine in the pharmaceutical and lab setting is synthesized through a combination of cysteine, methionine and vitamin E. It is naturally produced in testicles of many mammals. Urban legends surrounding the source of taurine have included bull urine extract and bull semen. While it’s true that taurine is found in both sources, it is not the source of taurine in the pharmaceutical or food industry. And while taurine is sometimes extracted from the intestines of cattle, many food industry sources, including the popular energy drink Red Bull,  make efforts to use synthesized sources that are vegetarian friendly.

Physiological roles

Taurine is conjugated via its amino terminal group with chenodeoxycholic acid and cholic acid to form the bile salts sodium taurochenodeoxycholate and sodium taurocholate. The low pKa (1.5) of taurine’s sulfonic acid group ensures that this moiety is negatively charged in the pH ranges normally found in the intestinal tract and thus improves the surfactant properties of the cholic acid conjugate, which can be found in many energy drinks today. Taurine has also been implicated in a wide array of other physiological phenomena including inhibitory neurotransmission, long-term potentiation in the striatum/hippocampus, membrane stabilization, feedback inhibition of neutrophil/macrophage respiratory bursts, adipose tissue regulation, calcium homeostasis and recovery from osmotic shock. It also acts as an antioxidant. .

Prematurely born infants who lack the enzymes needed to convert cystathionine to cysteine may become deficient in taurine. Thus, taurine is a dietary essential nutrient in these individuals and is often added to many infant formulas as a measure of prudence. There is also evidence that taurine is beneficial for adult human blood pressure and possibly, the alleviation of other cardiovascular ailments. Recent studies have also shown that taurine can influence (and possibly reverse) defects in nerve blood flow, motor nerve conduction velocity, and nerve sensory thresholds in experimental diabetic neuropathic rats. Taurine levels were found to be significantly lower in vegans than in a control group on a standard American diet. Plasma taurine was 78% of control values, and urinary taurine 29%.

According to animal studies, taurine produces anxiolytic effect and may act as a modulator or anti-anxiety agent in the central nervous system.

Taurine is necessary for normal skeletal muscle functioning. This was shown by a 2004 study, using mice with a genetic taurine deficiency. They had a nearly complete depletion of skeletal and cardiac muscle taurine levels. These mice had a reduction of more than 80% of exercise capacity compared to control mice. The authors expressed themselves as “surprised” that cardiac function showed as largely normal (given various other studies about effects of taurine on the heart).

Taurine is also used in some contact lens solutions.

Taurine has also been shown in diabetic rats to decrease weight and decrease blood sugar. According to one study, it has no effect on insulin secretion or insulin sensitivity in humans. However, there is evidence that taurine may exert a beneficial effect in preventing diabetes-associated microangiopathy and tubulointerstitial injury in diabetic nephropathy.

In humans suffering essential hypertension, taurine supplementation resulted in measurable decreases in blood pressure