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Theanine

Health Benefits, Uses, Side Effects & More

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Updated August 02, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Theanine (sometimes referred to as "L-theanine") is an amino acid found naturally in green tea. Also available in supplement form, theanine is said to offer a number of health benefits.

Health Benefits of Theanine:

To date, few clinical trials have tested the health effects of theanine. However, preliminary research indicates that theanine may offer certain health benefits. Here's a look at some key study findings:

1) Stress

Theanine may help reduce the negative effects of stress, according to a small study published in Biological Psychology in 2007. In an experiment involving 12 people, researchers found theanine-treated participants were less likely to experience an increase in heart rate when performing a stressful task.

See Natural Remedies For Anxiety and also Supplements For Stress Relief.

2) Immunity

Taking green-tea-derived theanine and antioxidants in supplement form may help prevent the flu, suggests a study published in BMC Complementary and Alternative Medicine in 2011. Every day for five months, the study's 197 participants took either a placebo or a capsule containing theanine and catechins (a class of antioxidants found in green tea). Results revealed that incidence of flu was significantly lower in the theanine/catechin group (compared to the placebo group).

Learn 5 Ways To Boost Your Immune System Naturally and get the scoop on 5 Foods For Boosting Your Immune System.

3) Brain Health

A 2010 study from Nutritional Neuroscience suggests that a combination of theanine and caffeine may help improve cognitive performance. For the study, 44 young adults took either a placebo or a combination of theanine and caffeine prior to performing a demanding cognitive task. Researchers found that the combination of theanine and caffeine significantly improved accuracy and alertness and helped to increase focus while performing the task.

Additionally, findings from an animal-based study published in Free Radical Biology & Medicine in 2009 suggest that theanine may inhibit buildup of amyloid beta (a substance that forms the brain plaques associated with Alzheimer's disease).

4) Depression

Theanine may help relieve depression, according to an animal-based study published in Phytotherapy Research in 2011. In tests on mice, scientists discovered that theanine produced an "antidepressant-like effect."

See Natural Remedies For Depression for other ways to help fight depression naturally.

5) Weight Loss

Theanine shows promise as a weight loss aid, according to animal-based research published in the journal In Vivo in 2004. In an experiment involving mice fed green tea powder, researchers found that theanine and caffeine found in the powder appeared to prevent weight gain and fight the buildup of fat.

Theanine is just one supplement that is used to shed pounds. Learn about 15 Popular Weight Loss Supplements.

Common Uses for Theanine:

Proponents claim that theanine can help with the following health problems:

Theanine is also purported to increase concentration, promote weight loss, and boost the immune system. In addition, some proponents suggest that theanine can prevent stroke, Alzheimer's disease, and some forms of cancer.

Safety:

To date, little is known about the safety of taking theanine supplements in the long term. While theanine is generally considered safe when consumed in green tea, the National Institutes of Health caution against drinking more than five cups of green tea daily. Due to the caffeine content, excessive consumption of green tea may trigger certain side effects (such as headache, insomnia, irritability, diarrhea, and heartburn).

There's also some concern that taking theanine in combination with sedatives, lipid-lowering medications, and/or drugs used in chemotherapy may produce harmful effects.

Where to Find Theanine Supplements:

Widely available for purchase online, theanine supplements are sold in many natural-food stores and in stores specializing in dietary supplements.

Using Theanine for Health:

While increasing your theanine intake by consuming green tea on a regular basis may help enhance your overall health, it's important to consult your doctor before using theanine supplements for any health condition.

Sources

Bryan J. "Psychological effects of dietary components of tea: caffeine and L-theanine." Nutr Rev. 2008 Feb;66(2):82-90.

Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. "The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness." Nutr Neurosci. 2010 Dec;13(6):283-90.

Kakuda T. "Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction." Pharmacol Res. 2011 Aug;64(2):162-8.

Kim TI, Lee YK, Park SG, Choi IS, Ban JO, Park HK, Nam SY, Yun YW, Han SB, Oh KW, Hong JT. "l-Theanine, an amino acid in green tea, attenuates beta-amyloid-induced cognitive dysfunction and neurotoxicity: reduction in oxidative damage and inactivation of ERK/p38 kinase and NF-kappaB pathways." Free Radic Biol Med. 2009 Dec 1;47(11):1601-10.

Kimura K, Ozeki M, Juneja LR, Ohira H. "L-Theanine reduces psychological and physiological stress responses." Biol Psychol. 2007 Jan;74(1):39-45.

Kakuda T. "Neuroprotective effects of the green tea components theanine and catechins." Biol Pharm Bull. 2002 Dec;25(12):1513-8.

Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM. " Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial." BMC Complement Altern Med. 2011 Feb 21;11:15.

Nobre AC, Rao A, Owen GN. "L-theanine, a natural constituent in tea, and its effect on mental state." Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8.

Owen GN, Parnell H, De Bruin EA, Rycroft JA. "The combined effects of L-theanine and caffeine on cognitive performance and mood." Nutr Neurosci. 2008 Aug;11(4):193-8.

Yin C, Gou L, Liu Y, Yin X, Zhang L, Jia G, Zhuang X. "Antidepressant-like effects of L-theanine in the forced swim and tail suspension tests in mice." Phytother Res. 2011 Nov;25(11):1636-9. doi: 10.1002/ptr.3456.

Zheng G, Sayama K, Okubo T, Juneja LR, Oguni I. "Anti-obesity effects of three major components of green tea, catechins, caffeine and theanine, in mice." In Vivo. 2004 Jan-Feb;18(1):55-62.

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