Written by Greg Arnold, DC, CSCS. Those taking theanine reduced heart rate by 6% and reaction time by 14% compared to the control group.

The relaxing properties of tea have been known for decades, possibly due to an amino acid called L-theanine, known to affect brain activity (1). In 2009, a study showed that four cups of green tea per day is “associated with a lower prevalence of depressive symptoms in the community-dwelling older population” compared to drinking less than one cup per day (2). The average cup of green tea is estimated to contain 20 mg of L-theanine (8) , so it would take 10 cups of tea per day to provide the dose tested below.

Now a new study (3) suggests that L-theanine may even affect reaction time. In the study, 18 healthy subjects between the ages of 18 and 20 were split into either “high anxiety” (8 subjects) or “minimal anxiety” (10 subjects) groups according to their scores on the manifest anxiety scale (4). The minimal and high anxiety subjects were given either one dose of either L-theanine 200 mg or placebo for a total of four different testing groups (minimal anxiety-placebo, minimal-theanine, high anxiety-placebo, high-theanine). Sixty minutes after supplementation, the researchers measured reaction time response, heart rate, and alpha brain waves. The participants also completed the State-Trait Anxiety Inventory (5) to assess anxiety levels.

The 200 mg of theanine dosage was chosen as it has been used in previous research studies from 1999 (6) and 2004 (7).  The researchers found significant differences between the L-theanine and placebo groups in the high anxiety group for brain activity, heart rate, and response time but no significant differences in the low anxiety group. After 1 hour, the L-theanine subjects in the high anxiety group had a 6% increase in alpha waves (105.6% vs. 99.6% of pre-study values), 6% lower heart rate (93.2% vs. 99.1% of pre-study values), and a 15% decrease in reaction time, compared to a 1% decrease in reaction time in the placebo group.

The change in brain waves may be due to L-Theanine’s ability to increase levels of brain chemical called GABA (9) which may have been responsible for the reaction time decrease. The researchers concluded that “L-theanine clearly has a pronounced effect on attention performance and reaction time response in healthy subjects prone to have high anxiety.”

Source: Higashiyama, Akiko, et al. “Effects of L-theanine on attention and reaction time response.” Journal of Functional Foods 3.3 (2011): 171-178.

Copyright © 2011 The Combustion Institute. Published by Elsevier Ltd

Posted August 4, 2011.

References:

  1.  Juneja LR.  (1999). L-Theanine – A unique amino acid of green tea and its relaxation effect in humans. Trends in Food Science & Technology, 1999;10(6–7), 199–204.
  2.  The World Health Organization. The World Health Report 2004: Changing History, Annex Table 3: Burden of disease in DALYs by cause, sex, and mortality stratum in WHO regions, estimates for 2002. Geneva: WHO, 2004.
  3.  Higashiyama, A. et al., Effects of L-theanine on attention and reaction time response, Journal of Functional Foods (2011), doi:10.1016/j.jff.2011.03.009.
  4.  Taylor, J. A. (1953). A personality scale of manifest anxiety. Journal of Abnormal and Social Psychology, 48(2), 285–290 (Japanese version of translation 1985).
  5. Speilberger, C. D., Gorushi, R. L., & Lushene, R. D. (1970). STAI manual for the State-Trait Anxiety Inventory. Palo Alto, CA: Consulting Psychologist Press.
  6.  Kobayashi, K. Effects of L-theanine on the release of alpha-brain waves in human volunteers. Nippon Nogeikagaku Kaishi 1998; 72, 153–157.
  7. Lu, K. The acute effects of Ltheanine in comparison with alprazolam on anticipatory anxiety in humans. Human Psychopharmacology 2004; 19(7), 457–465.
  8.  “L-Theanine” – Wikipedia.
  9.  Juneja, L. R., Chu, D. C., Okubo, T., Nagato, Y., & Yokogoshi, H.  L-Theanine – A unique amino acid of green tea and its relaxation effect in humans. Trends in Food Science & Technology 1999; 10(6–7), 199–204.