According to a paper from Anhui Agricultural University in China, theanine can protect liver tissue, minimising damage to the liver from chronic inflammation and its resultant diseases. The amino acid was found to increase antioxidant enzyme activity in mice, and to improve the human immune system.
The review stated: “More than 10% of the global population is estimated to be affected by chronic liver disease”, adding that “the incidence of chronic liver disease has been gradually increasing worldwide”.
It also noted that despite the progress made in the prevention and treatment of liver diseases, “the availability of treatments and the outcomes of individuals with chronic liver disease are still not ideal”.
To date, tea is the only known dietary source of theanine. Unlike catechins, which are present mostly in unfermented green teas but not in highly fermented black teas, theanine levels remain largely unaffected by the fermentation process, and are consistent in both green and black teas. This makes it the compound most likely responsible for liver protection.
When taken orally, theanine — either in its pure form or in tea — is absorbed fairly quickly by the small intestine before being metabolised in the intestine and liver.
A study on the effects of theanine on the liver showed that when it was administered to mice prior to ethanol exposure, it fully restored the mice’s baseline liver functions. These results bode well for drinkers, since they imply that theanine can help prevent ethanol-induced liver injury.
Apart from its hepatoprotective qualities, theanine has also been shown to have favourable effects on the overall immune system. This is especially true for the elderly, who tend to be more vulnerable to the flu.
According to the review, “The oral co-administration of theanine and cystine before vaccination can enhance immune response to the influenza vaccine in elderly persons with low total protein and haemoglobin levels.”
Research on the health benefits of theanine is still ongoing, and “additional evidence to support the health-promoting effects of theanine when consumed at levels consistent with current dietary guidelines is anticipated”.
Source: Asia Pacific Journal of Clinical Nutrition
"Theanine: The unique amino acid in the tea plant as an oral hepatoprotective agent"
Authors: Dongxu Wang, Qiang Gao, Taotao Wang, Frank Qian, Yijun Wang