Theanine (or L-theanine a specific form of theanine) is an amino acid analog of the amino acids L-glutamic acid and L-glutamine and is found primarily in black, green, and white teas prepared from Camellia sinensis. It's uncommon in the typical Western diet.
Is it safe? Are there side effects?
Yes, L-theanine is classified as GRAS (generally regarded as safe) by the FDA.
Effects on Cognition
The general picture that emerges from L-theanine research is anti-stress effects, with the strongest hypothesis being that anti-glutamate receptor activity is the primary driver of this effect. In particular, work from Kimura et al 2002 demonstrated that stress, measured subjectively by the state trait anxiety index and objectively by heart rate variability, are significantly reduced as a result of L-theanine administration during a stressful task.
There is also evidence to suggest that L-theanine administration prior to stress in academic settings can act to reduce stress levels as measured by questionnaires and salivary alpha-amylase (a marker for stress).
L-theanine supplementation has also been shown to increase brain α-waves (8-10 Hz range) which are associated with reduced stress and anxiety. Beyond relaxation, increased α-waves are associated with selective attention mechanisms and mental alertness. These altered wave functions are said to be evidence that theanine has 'relaxing and attention promoting' properties. There's also literature that report increased theta wave function which is associated with learning and memory.
Interestingly, in animal and human studies, high levels of stress are well known to result in cognitive and health deficits. In one study in mice, L-theanine reversed the lifespan reduction, cognitive deficits, and behavioral depression associated with chronic stress. In another study in mice, L-theanine was shown to reverse 3 stress-induced, depression-like phenotypes in mice. These data point to robust effects of L-theanine on a variety of general and cognitive health correlates that are impacted by stress.
By itself, the effects of L-theanine on attention is not pronounced, however, there is a strong synergism between Caffeine and L-theanine for improving attention.
Caffeine & L-theanine
Caffeine and L-theanine can act synergistically to improve alertness and attention. L-theanine can also potentially reverse some of the less favorable physiological effects of caffeine - including increased blood pressure, and reduced flow of oxygenated blood to the head.
- Unno, K., Tanida, N., Ishii, N., Yamamoto, H., Iguchi, K., Hoshino, M., . . . Yamada, H. (2013). Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary alpha-amylase activity, trait anxiety and subjective stress. Pharmacol Biochem Behav, 111, 128-135. doi:10.1016/j.pbb.2013.09.004
- Unno, K., Fujitani, K., Takamori, N., Takabayashi, F., Maeda, K., Miyazaki, H., . . . Hoshino, M. (2011). Theanine intake improves the shortened lifespan, cognitive dysfunction and behavioural depression that are induced by chronic psychosocial stress in mice. Free Radic Res, 45(8), 966-974. doi:10.3109/10715762.2011.566869
- Yin, C., Gou, L., Liu, Y., Yin, X., Zhang, L., Jia, G., & Zhuang, X. (2011). Antidepressant-like effects of L-theanine in the forced swim and tail suspension tests in mice. Phytother Res, 25(11), 1636-1639. doi:10.1002/ptr.3456
- Kakuda, T., Nozawa, A., Sugimoto, A., & Niino, H. (2002). Inhibition by theanine of binding of [3H]AMPA, [3H]kainate, and [3H]MDL 105,519 to glutamate receptors. Biosci Biotechnol Biochem, 66(12), 2683-2686.
- Yokogoshi, H., Kato, Y., Sagesaka, Y. M., Takihara-Matsuura, T., Kakuda, T., & Takeuchi, N. (1995). Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats. Biosci Biotechnol Biochem, 59(4), 615-618.
- Kakuda, T., Nozawa, A., Unno, T., Okamura, N., & Okai, O. (2000). Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat. Biosci Biotechnol Biochem, 64(2), 287-293. doi:10.1271/bbb.64.287