Tea, L‑theanine and a calmer mind

After water, tea is the most popular drink in the world. We turn to it for comfort, for a break in the day, and increasingly, for its claimed mood‑calming powers. Scroll through social media and you’ll find no shortage of claims that tea, or more so one of its bioactive compounds called L‑theanine, are a natural answer to stress and anxiety. In this podcast episode, I take a closer look at those claims through the lens of a new review that pulled together clinical trials on green tea, its key bioactive compounds, and mood with a particular focus on L‑theanine and anxiety.

Links referred to in the podcast

• Thinking Nutrition podcast episode 12 on tea and health https://thinkingnutrition.buzzsprout.com/808853/episodes/3156961-drink-tea-and-carry-on
• Systematic review on tea and its effects on mood https://pubmed.ncbi.nlm.nih.gov/40722728

Episode transcript
To access the full episode transcript, go to the following link and select the individual podcast episode and then click on the ‘Transcript’ tab https://thinkingnutrition.buzzsprout.com

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Transcript

After water, tea is the most popular drink in the world. We turn to it for comfort, for a break in the day, and increasingly, for its claimed mood‑calming powers. Scroll through social media and you’ll find no shortage of claims that tea, or more so one of its bioactive compounds called L‑theanine, are a natural answer to stress and anxiety. In today’s podcast, I’m going to take a closer look at those claims through the lens of a new review that pulled together clinical trials on green tea, its key bioactive compounds, and mood with a particular focus on L‑theanine and anxiety.

Let’s start off this podcast by setting the scene about tea itself. Because when I say ‘tea’, I’m talking about the classic varieties that come from the plant Camellia sinensis. From this one shrub we get black tea, green tea, white tea and oolong tea. All of them start life as the same leaves, but what happens after picking and depending on how much they’re oxidised or fermented, determines whether they end up in your cup as a strong black tea, a grassy green, or something in between.

For green tea, the tea leaves are harvested then quickly heated and dried to prevent too much oxidation and fermentation from occurring that would otherwise turn the green leaves brown and alter their fresh-picked flavour.

For black tea, tea leaves are exposed to air to allow them to ferment for several hours by natural enzymes found in the leaf. This oxidation process turns leaves a deep brown colour and during this process, the flavour is intensified. The leaves are then left as such or are heated, dried and crushed. Black tea has the highest content of caffeine of the different tea varieties but is still much less than a regular cup of coffee.

Oolong tea is produced by partial oxidation of the tea leaf so is intermediate between the processes used to make green and black tea.

The more processed the tea leaf, the lower the levels of some of its bioactive polyphenols, but even a standard black tea is still a rich source of these compounds. It’s these polyphenols, particularly a family called catechins in green tea and theaflavins in black tea, along with moderate amounts of caffeine and a unique amino acid called L‑theanine, that are thought to underpin many of tea’s health effects.

And that last one, L-theanine, is worth exploring in a bit more detail. Chemically, it looks a lot like glutamate, and since it can cross the blood brain barrier it has the potential to interact with glutamate receptors in the brain and help to inhibit glutamate’s activity. That’s important, because glutamate is the main excitatory neurotransmitter in the brain. Too much glutamate activity is linked to anxiety and neurotoxicity so controlling that system is one way to potentially dampen stress responses. L-theanine can also boost calming neurotransmitters like GABA, serotonin and dopamine, which can help to reduce stress and improve focus and concentration.

In an earlier podcast, episode 12, I did a deep dive into many of the health effects of tea so I’m not going to go over that ground here today. But if you want to check out that episode, I’ll link to it in the show notes. https://thinkingnutrition.buzzsprout.com/808853/episodes/3156961-drink-tea-and-carry-on

What I do want to talk about in this episode is the effect of tea on mood and mental health. Tea is one of the popular complimentary tools that people may turn to to help calm and soothe an over-active brain.

The mixture of bioactive compounds found in tea are thought to act on the brain through a combination of antioxidant, anti-inflammatory and neurosignalling mechanisms, helping to prevent neuroinflammation and neurotransmitter dysfunction. There is a lot more going on than that one simple sentence portrays, but for this podcast, I want to put that to the side and take the next step to see if drinking tea, or supplementing with the bioactive compounds it contains, can give some real-world brain and mood benefits.

And for this, I want to profile a newly published systematic review. The research team set out with a specific question: when you look only at randomised controlled trials in adults, what effect does green tea, green tea extracts, or its main bioactive compounds like L‑theanine and polyphenol catechins have on mood disorder symptoms?

In total, they could look at 13 randomised controlled trials with 7 trials using one of the bioactive compounds found in green tea given as a supplement while 6 trials used green tea extract, matcha or traditional green tea. Eleven trials included people without known health conditions, and two trials included participants with a mood disorder. And I’ll link to the review in the show notes. https://pubmed.ncbi.nlm.nih.gov/40722728

So, what did they find? Let’s start with L‑theanine as this was the most interesting finding. There were several studies that could show it led to improved sleep quality, reduced anxiety symptoms, and reduced stress. Doses used across the trials ranged from 200 to 400 milligrams per day which is in the ballpark for what is recommended in many commercial L-theanine supplements, but about 10-times more than you’ll find in a cup of tea. The effect sizes here though were modest, but they were measurable and they showed up in different countries, populations and study designs.

The trials with L-theanine proved to be the high-water mark because studies with green tea extract and isolated catechin supplements were more mixed, but some positive signals were seen although not a lot of studies were available to analyse. And when it came to drinking green tea, one study using 3 grams of matcha daily for 15 days could show a reduction in anxiety symptoms while one using green tea powder could show reduced depression symptoms.

Taken as a whole, the authors summarised the mood findings like this: across 13 trials, they saw improvements in depressive symptoms in four studies, anxiety in six, stress in five, and sleep in one.

But now for the downsides. Most of the trials were small with sample sizes often in the 20 to 80 range and with short intervention durations of up to four to twelve weeks. Populations varied from healthy students under exam stress, through to people with major depression, schizophrenia or HIV‑associated depression. Because the studies included a wide variety of interventions and only a small number evaluated the efficacy of specific interventions for a given outcome, it remains unclear which green tea interventions are most effective for improving mental health.

With the disclaimer of the limitations of the review, how best to translate the findings into practical advice for someone grappling with anxiety or stress and wondering if a daily green tea habit can help? Let’s bring this back down to the level of the teacup.

Firstly, if you enjoy drinking tea, this body of evidence gives you one more reason to feel good about that habit. Tea, especially green tea and matcha, appears to have small but meaningful, effects on anxiety and perceived stress, especially when consumed regularly. There’s also some early evidence that they can improve depressive symptoms and sleep in certain groups.

Secondly, when it comes to L‑theanine supplements specifically, the doses that have shown benefits in clinical trials tend to be in the 200 to 400 milligrams per day range. A standard cup of tea might give you somewhere around 20 to 40 milligrams, depending on how strong you brew it with the highest levels in matcha because you consume all of the tea leaves, rather than discard most of them. So regular tea drinking will contribute, but to reach trial‑like doses, you’re either looking at multiple cups of high‑theanine teas like matcha, or a standalone L‑theanine supplement.

Is that worth doing? For someone with mild anxiety or a lot of day‑to‑day stress who is already doing the big‑ticket lifestyle things like getting enough sleep, moving their body and eating well then a short trial of L‑theanine at evidence‑based doses could be reasonable, provided you’re not using it to bypass proper assessment for more significant mental health issues. In the reviewed studies, L‑theanine was generally well tolerated.

Green tea extracts and high‑dose catechin polyphenol supplements are where I’d be more cautious. While the trials in this review did not flag major safety problems over weeks of use at the doses used, other literature outside this paper have raised concerns about liver toxicity at high doses in some people. That’s more of a supplement issue than a brewed tea issue, but it’s a reminder that more is not always better.

And finally, perhaps the most important point. If you are experiencing persistent low mood, significant anxiety, or sleep disturbance that is affecting your functioning, the most evidence‑based path still runs through proper medical and psychological care. A teapot, no matter how beautifully brewed, cannot stand in for therapy or medication when those are indicated.

So, let’s wrap all this up. Tea brings together a unique mix of caffeine, polyphenols and L‑theanine. And while the research so far into its effects on mood still has quite some way to go, the direction of travel is encouraging. Though I would say that for the ‘supplement curious’, it could be worth doing a bit more of your own research into L-theanine to see what sort of mileage you could get from it. If nothing else though, it tells us that enjoying a regular cup or two of tea is doing more than just warming your hands.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on, or else head over to my webpage at www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

If you find this podcast of value, then please consider sharing it with your friends and colleagues. This all helps to increase the reach of the podcast, which means a big win for credible evidence-based nutrition messages and making the world a slightly less confusing place.

I’m Tim Crowe and you’ve been listening to Thinking Nutrition.