'L-Theanine' Impostors Blocked at Intestinal Border

Study confirms poor absorption, unknown safety and efficacy
of racemic mixtures of D- and L-theanine

May 8, 2005, Minneapolis – Your right shoe won’t fit on your left foot. This fashion dictum carries through to metabolism and biology, even with constituents found in tea. A new study in the journal Chirality suggests that dietary supplements that do not use pure L-theanine may not deliver L-theanine benefits because they “fit” poorly into the body.

Researchers from Iowa State University study compared the pharmacokinetics of L-theanine, D-theanine, and an ingredient commercially market as “L-theanine” that actually was a racemic mixture of theanine (a 50:50 D- and L-theanine mixture, also known as a racemate). “Our study published last year uncovered the fact that some ingredients being sold and marketed as “L-theanine” are indeed racemates of theanine”, stated Dr. Daniel Armstrong from ISU’s Department of Chemistry and the director of the research team in this investigation.

In the current study, Armstrong’s team orally supplemented rats with three different theanine ingredients: a commercially available “L-theanine” that actually was a racemate, pure D-theanine, and pure L-theanine. They then followed blood concentrations, urinary excretion, and a marker of theanine metabolism in the blood. “Our results quite convincingly demonstrate that, at least in animals, their metabolism preferentially selects L-theanine, beginning with absorption in the gut.” When equal amounts of L-theanine were administered, coming from pure L-theanine or the racemate, the concentration seen in the blood was greater with the pure L-theanine. “What poses a potential concern to the consumer is the safety and efficacy of theanine racemates sold as L-theanine, as this is a complete unknown,” he added.

Virtually all of the clinical studies and the majority of the animal studies that have been performed assessing the bioactivity of theanine have used Suntheanine. “Examination of the urinary excretion data from Dr. Armstrong’s study also indicates a trend for greater L-theanine excretion when supplemented as the racemate,” offered Dr. Lekh Raj Juneja, Executive Vice President of Taiyo Kagaku, the manufacturer of Suntheanine. “When it comes to evidence of safety and efficacy, and now pharmacokinetics, Suntheanine casts a very long shadow relative to the many ingredients that claim to be “pure L-theanine”.

Suntheanine and Taiyo have been successful in creating an awareness and demand for L-theanine, in addition to a suite of international patents. “Simple HPLC analysis cannot discriminate between D- and L-theanine yet a number of companies are relying upon this method to assert that they have the pure L-isomer,” declared Scott Smith, Vice President of Taiyo International in Minneapolis. “Our patented enzymatic synthesis method “locks” in the L-isomer and thus gives us pure L-theanine every batch. Suntheanine is an elegant example of where chemistry dictates biology.”

The study was supported by an ISU fund to Dr. Armstrong.


Taiyo International is the North American sales office for Taiyo Kagaku Japan, a leading manufacturer of functional ingredients for the food, beverage and dietary supplement industries. Taiyo focuses on the development of innovative ingredients, derived from natural sources, to further develop the body’s ability to protect and manage one’s health.

Suntheanine is Taiyo’s exclusive brand of pure L-theanine, supported by extensive clinical trials. Suntheanine is protected by over 40 U.S. and international patents for its various physiological efficacies and L-isomer-specific production processes.

Scott Smith
T: 763-398-3003
E: [email protected]

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