L-theanine for women: are there any particularities

L-theanine is an amino acid from tea that women often choose for calm concentration and better sleep. But does it affect the female body differently? The editorial team has analyzed what the research says and singled out the situations in which women should be more attentive: the cycle, contraception, pregnancy and iron.

What is known about L-theanine in general

L-theanine is a non-proteinogenic amino acid naturally found in the leaves of the tea plant (Camellia sinensis). It is credited with the characteristic "calm tone" of tea, in contrast to the harsher stimulation of coffee. As a supplement, theanine is sold as a means of reducing stress and improving concentration and sleep.

The mechanism of action has been studied only in part. Theanine crosses the blood-brain barrier and, according to experimental work, affects glutamatergic transmission and the levels of GABA, dopamine and serotonin. Early EEG studies (Nobre et al.) showed an increase in alpha rhythm — the brain activity characteristic of a calm but alert state.

The most convincing data concern the combination of theanine with caffeine: in randomized studies (Owen et al., 2008; Haskell et al., 2008) this pairing improved the speed and accuracy of attention tasks and reduced subjective fatigue. The effects of theanine alone on stress and sleep are moderate; the systematic review by Williams et al. (2020) rated them as promising but based on small studies.

So, before discussing particularities for women, it is important to understand: theanine is a mild supplement with a modest evidence base, not a sedative drug.

Does theanine act differently on women

The short answer is that there is essentially no data on sex differences in the action of theanine. Most studies were conducted on small mixed samples, and a separate analysis for women was usually not published. The Japanese randomized study by Hidese et al. (2019), in which participants received 200 mg of theanine per day for four weeks, included both men and women and showed improvements in measures of stress, sleep and certain cognitive functions compared with placebo.

There are no physiological reasons to expect a fundamentally different action: theanine is not a hormone, does not, as far as is known, affect the levels of estrogen or progesterone, and has no known mechanisms specific to the female body.

However, there are several contexts in which women use theanine more often, or in which its use has nuances. These are what we will consider next: the menstrual cycle, the interaction with caffeine while on hormonal contraception, pregnancy and breastfeeding, and iron.

The editorial team emphasizes: the diagram above reflects not the strength of the effect but only how much research exists in each area.

The menstrual cycle and PMS

In the luteal phase of the cycle, some women note irritability, anxiety and worse sleep. Theanine is sometimes marketed as a remedy for premenstrual syndrome. A few small Japanese studies reported a reduction in certain symptoms, but these were studies of limited design, and there are no recommendations from professional societies regarding the use of theanine for PMS.

In practical terms this means that theanine can be tried as a mild aid for falling asleep more easily and easing tension on these days, but one should not expect an effect comparable to the treatment a gynecologist prescribes for pronounced PMS or premenstrual dysphoric disorder.

If the symptoms significantly affect training, work and relationships, it is worth seeing a doctor: there are treatment methods with proven efficacy, and other conditions may be hiding behind severe symptoms.

For female athletes who keep a cycle diary, it is useful to note their well-being with and without the supplement — this makes it possible to honestly assess the individual response.

Caffeine, contraception and theanine

Many women take theanine together with caffeine — as part of pre-workout formulas or simply with their morning coffee. There is an important nuance here: combined oral contraceptives slow the metabolism of caffeine by inhibiting the enzyme CYP1A2. Caffeine stays in the blood longer, and a usual dose can cause anxiety, tachycardia and worse sleep.

Theanine partly smooths out the subjective "jitteriness" from caffeine but does not cancel its physiological action. That is why the editorial team advises women on hormonal contraception to assess the total dose of caffeine from all sources and not to increase it simply because a product contains theanine.

When it comes to iron, a distinction should be made: isolated theanine itself, as far as is known, does not interfere with iron absorption, but if you get theanine from large amounts of green or black tea, the polyphenols in tea reduce the absorption of non-heme iron. For women with heavy periods and endurance athletes, this is practically significant.

How to take it: practical guidelines

Theanine is an ordinary dietary supplement, and for healthy adult women the practical guidelines are the same as for men:

• studies most often used 100–200 mg per dose, with some using up to 400 mg per day;
• for concentration with caffeine, a ratio of about 2:1 (theanine : caffeine) has been studied, for example 100 mg of theanine with 50 mg of caffeine;
• for evening relaxation and sleep, theanine is taken without caffeine 30–60 minutes before bed;
• the effect is mild and develops over the course of an hour; noticeable "sedation" is not expected.

Side effects in studies were rare and mild: headache, slight stomach discomfort. No serious problems have been described in clinical work, but most of it lasted only a few weeks, so there is little data on long-term daily use.

Choose products from manufacturers who state the form (often the patented Suntheanine) and the dose per serving, rather than a "proprietary blend" without numbers.

During pregnancy and breastfeeding, the editorial team advises against taking theanine as a supplement without a doctor's approval — not because harm has been proven, but because its safety in these states has not been studied.

Editorial conclusions

There is no evidence that theanine acts differently on women than on men. The particularities concern context: the interaction with caffeine while on hormonal contraception, the lack of data on pregnancy and lactation, and the effect of tea on iron absorption.

As a mild aid for concentration paired with caffeine and for better relaxation in the evening, theanine has a reasonable benefit-risk ratio for healthy women.

We also recommend reading our articles "L-theanine after 40", "Rhodiola rosea for women: are there any particularities" and our review of caffeine in sports nutrition.

References

1. Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17(Suppl 1):167–168.
2. Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008;11(4):193–198.
3. Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol. 2008;77(2):113–122.
4. Hidese S, Ogawa S, Ota M, et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients. 2019;11(10):2362.
5. Williams JL, Everett JM, D'Cunha NM, et al. The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review. Plant Foods Hum Nutr. 2020;75(1):12–23.
6. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the safety of caffeine. EFSA J. 2015;13(5):4102.