Taurine concentrations in land plants are low or undetectable, but up to 1000 nmol/g wet weight have been found in algae.[7][8]
Chemical and biochemical features
Taurine exists as a zwitterionH3N+CH2CH2SO−3, as verified by X-ray crystallography.[9] The sulfonic acid has a low pKa[10] ensuring that it is fully ionized to the sulfonate at the PHs found in the intestinal tract.
In 1993, about 5000–6000 tonnes of taurine were produced for commercial purposes: 50% for pet food and 50% in pharmaceutical applications.[12] As of 2010, China alone has more than 40 manufacturers of taurine. Most of these enterprises employ the ethanolamine method to produce a total annual production of about 3000 tonnes.[13]
In the laboratory, taurine can be produced by alkylation of ammonia with bromoethanesulfonate salts.[14]
Taurine occurs naturally in fish and meat.[5][19][20] The mean daily intake from omnivore diets was determined to be around 58 mg (range 9–372 mg),[21] and to be low or negligible from a vegan diet.[5] Typical taurine consumption in the American diet is about 123–178 mg per day.[5]
Taurine is partially destroyed by heat in processes such as baking and boiling. This is a concern for cat food, as cats have a dietary requirement for taurine and can easily become deficient. Either raw feeding or addition of extra taurine can satisfy this requirement.[22][23]
Prematurely born infants are believed to lack the enzymes needed to convert cystathionine to cysteine, and may, therefore, become deficient in taurine. Taurine is present in breast milk, and has been added to many infant formulas, as a measure of prudence, since the early 1980s. However, this practice has never been rigorously studied, and as such it has yet to be proven to be necessary, or even beneficial.[25]
Energy drinks and dietary supplements
Taurine is an ingredient in some energy drinks in amounts of 1–3 g per serving.[5][26][27][28] A 1999 assessment of European consumption of energy drinks found that taurine intake was 40–400 mg per day.[21]
Research
Taurine is not regarded as an essential human dietary nutrient and has not been assigned recommended intake levels.[4] High-quality clinical studies to determine possible effects of taurine in the body or following dietary supplementation are absent from the literature.[5] Preliminary human studies on the possible effects of taurine supplementation have been inadequate due to low subject numbers, inconsistent designs, and variable doses.[5]
Safety and toxicity
According to the European Food Safety Authority (EFSA), taurine is "considered to be a skin and eye irritant and skin sensitiser, and to be hazardous if inhaled;" it may be safe to consume up to 6 grams of taurine per day.[6] Other sources indicate that taurine is safe for supplemental intake in normal healthy adults at up to 3 grams per day.[5][29]
A 2008 review found no documented reports of negative or positive health effects associated with the amount of taurine used in energy drinks, concluding, "The amounts of guarana, taurine, and ginseng found in popular energy drinks are far below the amounts expected to deliver either therapeutic benefits or adverse events".[30]
Animal dietary requirement
Cats
Cats lack the enzymatic machinery (sulfinoalanine decarboxylase) to produce taurine and must therefore acquire it from their diet.[31] A taurine deficiency in cats can lead to retinal degeneration and eventually blindness – a condition known as central retinal degeneration[32][33] as well as hair loss and tooth decay. Other effects of a diet lacking in this essential amino acid are dilated cardiomyopathy and reproductive failure in female cats.[34]
Decreased plasma taurine concentration has been demonstrated to be associated with feline dilated cardiomyopathy. Unlike CRD, the condition is reversible with supplementation.[35]
Taurine is now a requirement of the Association of American Feed Control Officials (AAFCO) and any dry or wet food product labeled approved by the AAFCO should have a minimum of 0.1% taurine in dry food and 0.2% in wet food.[36] Studies suggest the amino acid should be supplied at 10 mg per kilogram of bodyweight per day for domestic cats.[37]
Other mammals
A number of other mammals also have a requirement for taurine. While the majority of dogs can synthesize taurine, case reports have described a singular American cocker spaniel, 19 Newfoundland dogs, and a family of golden retrievers suffering from taurine deficiency treatable with supplementation. Foxes on fur farms also appear to require dietary taurine. The rhesus, cebus and cynomolgus monkeys each require taurine at least in infancy. The giant anteater also requires taurine.[38]
Birds
Taurine appears to be essential for the development of passerine birds. Many passerines seek out taurine-rich spiders to feed their young, particularly just after hatching. Researchers compared the behaviours and development of birds fed a taurine-supplemented diet to a control diet and found the juveniles fed taurine-rich diets as neonates were much larger risk takers and more adept at spatial learning tasks. Under natural conditions, each blue tit nestling receive 1 mg of taurine per day from parents.[39]
Taurine can be synthesized by chickens. Supplementation has no effect on chickens raised under adequate lab conditions, but seems to help with growth under stresses such as heat and dense housing.[40]
Fish
Species of fish, mostly carnivorous ones, show reduced growth and survival when the fish-based feed in their food is replaced with soy meal or feather meal. Taurine has been identified as the factor responsible for this phenomenon; supplementation of taurine to plant-based fish feed reverses these effects. Future aquaculture is expected to use more of these more environmentally-friendly protein sources, so supplementation would become more important.[41]
The need of taurine in fish is conditional, differing by species and growth stage. The Olive flounder, for example, has lower capacity to synthesize taurine compared to the rainbow trout. Juvenile fish are less efficient at taurine biosyntheis due to reduced cysteine sulfinate decarboxylase levels.[42]
^Irving CS, Hammer BE, Danyluk SS, Klein PD (October 1980). "13C nuclear magnetic resonance study of the complexation of calcium by taurine". Journal of Inorganic Biochemistry. 13 (2): 137–150. doi:10.1016/S0162-0134(00)80117-8. PMID7431022.
^Jacobson SG, Kemp CM, Borruat FX, Chaitin MH, Faulkner DJ (October 1987). "Rhodopsin topography and rod-mediated function in cats with the retinal degeneration of taurine deficiency". Experimental Eye Research. 45 (4): 481–490. doi:10.1016/S0014-4835(87)80059-3. PMID3428381.
^Shao A, Hathcock JN (April 2008). "Risk assessment for the amino acids taurine, L-glutamine and L-arginine". Regulatory Toxicology and Pharmacology. 50 (3): 376–399. doi:10.1016/j.yrtph.2008.01.004. PMID18325648. the newer method described as the Observed Safe Level (OSL) or Highest Observed Intake (HOI) was utilized. The OSL risk assessments indicate that based on the available published human clinical trial data, the evidence for the absence of adverse effects is strong for Tau at supplemental intakes up to 3 g/d, Gln at intakes up to 14 g/d and Arg at intakes up to 20 g/d, and these levels are identified as the respective OSLs for normal healthy adults.
^Clauson KA, Shields KM, McQueen CE, Persad N (2008). "Safety issues associated with commercially available energy drinks". Journal of the American Pharmacists Association. 48 (3): e55–63, quiz e64–67. doi:10.1331/JAPhA.2008.07055. PMID18595815. S2CID207262028.
^Burger IH, Barnett KC (1982). "The taurine requirement of the adult cat". Journal of Small Animal Practice. 23 (9): 533–537. doi:10.1111/j.1748-5827.1982.tb02514.x.
^Schaffer SW, Ito T, Azuma J (January 2014). "Clinical significance of taurine". Amino Acids. 46 (1): 1–5. doi:10.1007/s00726-013-1632-8. PMID24337931. (abstracts of animal citations used to provide list of species)
