There are few certainties in life, but one of them is that we all, without fail, will age. Aging is the nature of biological life and of the universe itself through entropy. But, just because it is inevitable doesn't mean we as a species have resigned ourselves to it. Significant amounts of effort have been spent looking for ways to fight aging and death, ranging from the mystical to the scientific, throughout all of human history.
While we haven't figured out a way to prevent aging, we've found many different ways to expand our lifespans, from the treatment of disease to the expansion of sanitation to modern medicine. And we're always looking out for more potential avenues to address either the side effects or the causes of aging.
One such possible mechanism comes from a humble molecule called L-Theanine, or simply Theanine. There has been some attention paid to this molecule in recent years, with some potentially promising results, but there are a few drawbacks that leave me skeptical for the time being. Before you go out and start buying theanine supplements, let's talk about the truth without all of the marketing.
Table of Contents
What is L-Theanine?
What is theanine in the first place?
Theanine is an amino acid of some sort. Actually, it's an amino acid analogue. Analogues are molecules that are structurally identical to one another but place their atoms in slightly different positions or use slightly different atoms in their makeup. Though they are structurally the same, they may not be functionally the same, which is a critical difference when talking about microbiology and biochemistry.
Theanine is a structural analogue of the proteinogenic amino acid glutamine, which is the most abundant free amino acid in our blood and is used in many different ways throughout the body. However, since Theanine is not a functional analogue of glutamine, we don't really need to dig into glutamine to understand theanine's function.
Theanine also comes in two forms, described as handedness. L-theanine is the left-handed version (but no, the L doesn't stand for left) and is common because it's found in tea leaves and some mushrooms. The other version, the right-handed D-theanine, is rarer and is not well studied. I bring this up because I'll be using the terms Theanine and L-Theanine interchangeably; D-Theanine isn't part of today's discussion either.
As mentioned, theanine comes primarily from tea, the camellia sinensis plant. That means all versions of tea with actual tea leaves – green, black, white, oolong, matcha – have it, but herbal teas and other plants do not. It's present in greater amounts in variations of tea that are shaded from sunlight, like matcha and gyokuro green. It's also found in some mushrooms, but the vast majority of the time when theanine is being discussed, it's coming from some form of tea.
Is there a recommended daily intake for theanine?
No. Theanine is not a critical or essential nutrient and is not required in your diet to be healthy.
Theanine has GRAS status in the United States. That is, it is Generally Recognized as Safe. It's broadly approved in foods in Japan, except for infant foods. Meanwhile, Germany restricts its addition to beverages other than those it's naturally in like tea. Slovenia prohibits its addition to non-alcoholic beverages.
In tea as a natural beverage, a single cup often contains around 6-7 mg of theanine, while others can have anywhere from 25 to 46 mg. This is a highly variable average, however; there's little information on whether or not preparation changes the amount, and whether or not steeping the same tea multiple times adds more or less, and other factors. It's estimated that the average Japanese citizen consumes around 20 mg of theanine per day, though this is also highly variable.
Theanine supplements, meanwhile, are often in the 200 mg to 500 mg range. At this level, theanine does not appear to have significant side effects; reports of headaches, nausea, dizziness, and similar side effects come from consuming large quantities of tea and the associated caffeine intake.
Why Do Some People Say L-Theanine Can Help with Longevity?
So, why has theanine been getting attention recently? Current marketing trends and supplement promoters are making claims that theanine can help reduce the effects of aging and cognitive decline.
Theanine has also been touted for relaxation and anti-anxiety effects, but most studies have not backed up these claims. What we're mostly concerned with today is the anti-aging possibilities.
Where do these claims come from?
The most frequently cited study is this one from June 2024. This study found that theanine functioned to activate certain molecular pathways to resist damage from ultraviolet radiation on roundworms.
Why roundworms? Research from all the way back in 1965 found that these roundworms serve two purposes in research:
- They have very fast life cycles, so the effects of various compounds, radiation, and other treatments on aging can be observed much more rapidly than in longer-lived organisms.
- Numerous studies over the decades have shown that effects observed in roundworms are unusually highly effective predictive value for similar effects in higher organisms. In other words, what works for roundworms is promising for other creatures, including humans.
Additionally, roundworms have been completely genetically sequenced and mapped, so there's a comprehensive knowledge of how they're put together, and even the smallest changes can be observed much more readily than they can be in larger organisms.
Back to the study. What did this roundworm study show about theanine?
Essentially, theanine helped improve how the roundworms functioned after exposure to UV-C radiation by helping boost energy production, repair damaged mitochondria, and clean up damage throughout cells.
If this was the only study, we could end the discussion here. However, there have been some other studies as well over the last few years that could lend some additional weight to the idea that theanine helps reduce the effects of aging.
Another study, published in May of 2024, examined the effects of theanine in L6 cells. L6 cells, put simply, are cell cultures from rats that are used for simple testing purposes where a more controlled environment is required and where testing on live rats is both unnecessary and potentially cruel. This study found that the impact of induced aging on the cells was reduced by administering theanine. A similar rat study of liver aging from 2019 had similar results.
A mice study from all the way back in 2011 also seemed to indicate theanine intake could improve lifespan, reduce cognitive dysfunction, and decrease behavioral depression in stressed mice.
In humans, many of the common effects of theanine, like regulating mood, reducing anxiety, and reducing stress levels, have not been reflected in most studies. Some, like this one from 2010, showed some benefit in patients with schizophrenia. That study was only two months long and involved only 60 patients, however.
Why I'm Not Excited for L-Theanine Just Yet
If you've read my blog or followed my YouTube channel, you know I'm always keeping an ear to the ground about new and interesting medical research, particularly when it involves aging, health, sleep, or exercise. I prefer to rely on large-scale human studies to base my recommendations, and I avoid anything that is untested. I also broadly dislike megadosing, as there are frequently negative effects associated with "too much of a good thing."
In the case of theanine, there's some good news and some bad news.
The good news is, there does not seem to be any serious side effects associated with large doses of theanine. When a standard "dose" from a cup of tea can be anywhere from 5 to 50mg of theanine, but a single supplement can be an order of magnitude more, you would expect at least some common side effects to be apparent, but none have been reported.
While this is good news for those who take large doses of theanine, it may also be bad news in terms of the efficacy of theanine as a supplement. The fact that it has no side effects may mean that it isn't being readily absorbed or that it isn't being processed in the body in an impactful way. After all, the only difference between an effect and a side effect is whether or not it's intended.
The bad news has to do with the studies showing promising anti-aging effects. As you may have noticed, none of them are human studies. Studies in mice, rats, and roundworms can all be useful. Roundworms, as mentioned above, are great for specific kinds of testing. Mice and rats are good for more complex biological tests that need testing beyond those on tissue samples or worms, but which aren't viable enough to be upgraded to human testing.
The problem is, until those effects are demonstrated in randomized, controlled trials, they aren't particularly meaningful to me. It's possible that those effects will bear out, but it's also possible that they won't or that theanine could interact with other bodily systems or with medications in a negative way. I wouldn't recommend an untested supplement, let alone a megadose of that supplement, without good reason.
For these reasons, I don't take theanine myself, either on its own or as part of MicroVitamin.
If you've decided you want to take theanine yourself, you have to decide how much you want and what form it should take. There are essentially two options available to you.
The first is tea. Drinking tea will provide you with some amount of theanine, though it will vary from cup to cup, from batch of tea to batch of tea, and even between different types of tea. If you simply want to make sure you're taking some amount of theanine, and don't feel the need to take very large doses, tea is an acceptable option.
There are two cautions I have for tea, however.
First, make sure you're only drinking it within the first four or so hours of your day after waking up in the morning. This has little to do with theanine and everything to do with the fact that tea contains caffeine, and caffeine will negatively impact your sleep if you take it too late in the day.
The second is that you should only drink tea in moderation. Theanine itself doesn't seem to have any side effects in large doses, but tea does, and drinking too much tea throughout a day can cause a variety of adverse effects depending on your sensitivity to the compounds and caffeine in each drink.
Finally, there are a wide range of theanine supplements available on the market, but again I personally wouldn’t take any of them.
And stay tuned. If human trials are performed and show that theanine has tangible beneficial effects, I'm certainly willing to revisit the subject.
Sources:
- PubChem – Theanine: https://pubchem.ncbi.nlm.nih.gov/compound/Theanine
- Memorial Sloan Kettering Cancer Center – L-Theanine: https://www.mskcc.org/cancer-care/integrative-medicine/herbs/l-theanine
- Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples: https://pmc.ncbi.nlm.nih.gov/articles/PMC4787341/
- ConsumerLab L-Theanine Supplements Review: https://www.consumerlab.com/reviews/l-theanine-supplements-review/l-theanine/
- L-Theanine Prolongs the Lifespan by Activating Multiple Molecular Pathways in Ultraviolet C-Exposed Caenorhabditis elegans: https://pmc.ncbi.nlm.nih.gov/articles/PMC11173996/
- L-theanine protects against D-galactose-induced aging in L6 skeletal muscle cells: https://www.sciencedirect.com/science/article/pii/S1756464624001373
- L-Theanine attenuates liver aging by inhibiting advanced glycation end products in D-galactose-induced rats and reversing an imbalance of oxidative stress and inflammation: https://www.sciencedirect.com/science/article/abs/pii/S0531556519306643
- Theanine intake improves the shortened lifespan, cognitive dysfunction, and behavioral depression that are induced by chronic psychosocial stress in mice: https://www.tandfonline.com/doi/abs/10.3109/10715762.2011.566869?journalCode=ifra20
- L-theanine prevent quinolinic acid induced motor deficit and striatal neurotoxicity: Reduction in oxido-nitrosative stress and restoration of striatal neurotransmitters level: https://www.sciencedirect.com/science/article/abs/pii/S0014299917304235?via%3Dihub
- L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study: https://pubmed.ncbi.nlm.nih.gov/21208586/
