Cognitive Benefits of L-Theanine Supplementation
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L-Theanine is a unique amino acid primarily found in green tea leaves (Camellia sinensis). Unlike most amino acids, L-Theanine is not used to build proteins but is prized for its subtle yet significant effects on the brain. Over the past two decades, research has illuminated how L-Theanine supplementation can support cognitive function, stress management, and mental performance.
How L-Theanine Works in the Brain
L-Theanine readily crosses the blood-brain barrier and modulates several neurotransmitter systems, including gamma-aminobutyric acid (GABA), dopamine, and serotonin. These changes contribute to its relaxing yet non-sedating effects, making it a popular supplement for cognitive health and stress reduction (1).
Key Cognitive Benefits of L-Theanine
1. Promotes Relaxation Without Drowsiness
L-Theanine increases alpha brain wave activity, which is associated with a state of “relaxed alertness.” This relaxation effect occurs without causing sedation or impairing cognitive function, making L-Theanine distinct from many other calming supplements (2).
- Evidence: In a randomized, placebo-controlled study, healthy adults who took 200 mg of L-Theanine showed increased alpha wave activity and reported greater feelings of relaxation compared to placebo (2).
2. Reduces Stress and Anxiety
L-Theanine supplementation has been linked to reduced physiological and psychological markers of stress. (lowering cortisol)
- Evidence: In a randomized controlled trial, participants who took 200 mg of L-Theanine before a stressful task showed lower heart rate and salivary immunoglobulin A responses, suggesting reduced acute stress (4).
- Additional findings: Several studies report that L-Theanine supplementation can lower subjective feelings of anxiety and tension in both healthy and high-stress populations (5).
3. Supports Cognitive Performance Under Stress
L-Theanine may help preserve cognitive function in stressful situations by promoting calmness and reducing the negative impact of stress on memory and attention.
- Evidence: Studies have shown that L-Theanine supplementation can reduce cognitive impairments associated with acute stress and help maintain performance in demanding tasks (4, 5).
Safety and Dosage
L-Theanine is considered very safe, with no known toxicity at typical supplemental doses (100–400 mg/day). Most studies use doses of 100–200 mg, either alone or in combination with caffeine.
Summary Table
| Benefit | Evidence Level | Typical Dose |
|---|---|---|
| Relaxation (non-sedating) | Strong | 100–200 mg |
| Improved attention & focus | Strong | 100–200 mg (with caffeine) |
| Reduced stress & anxiety | Moderate | 200 mg |
| Cognitive support under stress | Moderate | 200 mg |
References
- Nathan, P.J., Lu, K., Gray, M., & Oliver, C. (2006). The neuropharmacology of L-theanine (N-ethyl-L-glutamine): A possible neuroprotective and cognitive enhancing agent. Nutritional Neuroscience, 9(4), 193-200. Link
- Nobre, A.C., Rao, A., & Owen, G.N. (2008). L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pacific Journal of Clinical Nutrition, 17(S1), 167-168. Link
- Haskell, C.F., Kennedy, D.O., Milne, A.L., Wesnes, K.A., & Scholey, A.B. (2008). The effects of L-theanine, caffeine and their combination on cognition and mood. Biological Psychology, 77(2), 113-122. Link
- Kimura, K., Ozeki, M., Juneja, L.R., & Ohira, H. (2007). L-Theanine reduces psychological and physiological stress responses. Biological Psychology, 74(1), 39-45. Link
- Hidese, S., Ogawa, S., Ota, M., et al. (2019). Effects of chronic L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: A randomized controlled trial. Nutrients, 11(10), 2362. Link
