Can Green Tea Actually Make You Calmer And Sharper? Research Weighs In
There's a particular kind of afternoon slump when you're tired enough to want coffee, but wired enough to wonder whether another cup is really a good idea.
Green tea can feel like a middle ground.
You still get some caffeine, but you're also getting L-theanine, an amino acid naturally found in tea leaves. It's become popular in supplements aimed at focus and relaxation, and some people swear by the combination. But how much of that reputation is actually backed by research?
A recent mini-review of human trials1 took a closer look.
About the review
L-theanine is a naturally occurring amino acid found mainly in tea leaves and some mushrooms. Researchers have been interested in it because it may influence how we respond to stress while still allowing us to stay alert.
For this review, researchers pulled together existing human trials examining L-theanine in three areas: cognitive performance, stress and mood, and sleep quality.
They compared findings across previous research to see where the evidence was most consistent.
What researchers found
The results varied depending on the outcome.
For cognitive performance, L-theanine showed some potential at doses between 100 and 400 milligrams. Some studies found improvements in visual attention and processing speed, but it did not consistently improve reaction time or more complex thinking tasks.
The cognitive benefits also appeared more often when L-theanine was taken with caffeine.
The evidence was more consistent for stress. Doses of 200 to 400 milligrams were linked with lower perceived stress and changes in stress-related markers when participants were put in stressful situations.
L-theanine also did not appear to make people sleepy, which could make it appealing for someone who wants to feel calmer without feeling checked out.
Sleep quality showed another potential benefit. Research using 200 to 450 milligrams found that people tended to rate their sleep more favorably, although L-theanine did not significantly increase the amount of time they actually spent asleep.
Why the caffeine combination is interesting
The cognitive findings are particularly relevant if you already drink coffee or tea.
L-theanine did not consistently improve cognitive performance on its own, but some of the more positive findings appeared when it was combined with caffeine.
That may help explain why the two ingredients are often paired in supplements designed for focus.
Still, the evidence here is limited.
The cognitive studies involved relatively small groups, and researchers used different doses and tests. So while the combination is interesting, we can't say that L-theanine and caffeine will reliably produce a major cognitive boost for everyone.
A few ways to put this research into practice
You don't need to start taking an L-theanine supplement to make use of the research. A few simple options include:
- Try green tea as a lower-key afternoon option: You'll get L-theanine along with caffeine, rather than automatically reaching for another strong coffee.
- Pay attention to how caffeine feels: If coffee leaves you alert but jittery, swapping some of your caffeine intake for tea may be a simple way to see whether you feel better with a gentler dose.
- Keep expectations realistic: If you're interested in an L-theanine supplement, research has used 100 to 450 milligrams depending on the outcome being studied. These are research doses, not a recommendation for everyone, so check with a health care provider before starting a supplement, particularly if you take medications or other supplements, or you're managing a diagnosed condition like anxiety or a sleep disorder.
The takeaway
L-theanine's strongest case so far sits with stress and sleep quality, while the attention findings are smaller and often tied to caffeine. A cup of green tea is one way to test it out, or try pairing a supplement with your morning cup of coffee.