Why does a glass of tea on the balcony feel so different from a strong cup of coffee, even though both contain caffeine? Part of the answer is simply the ritual: the pause, the company, the mint or sage in the glass. Part of it may be a compound called L-theanine.
What L-theanine is
L-theanine is an amino acid found mainly in the leaves of the tea plant, Camellia sinensis. Unlike the amino acids that build protein, it is not one your body needs from food. Green, black and white teas all contain it, in amounts that vary with the leaf and how it was grown and processed. Shaded teas such as matcha tend to be richer in it.
Herbal drinks such as sage or anise tea come from different plants and do not provide it, unless they are blended with real tea.
What the research says
Studies on L-theanine are mostly small and short. A systematic review published in Plant Foods for Human Nutrition identified nine trials comparing an L-theanine supplement with a control and concluded that 200 to 400 milligrams a day may help reduce stress and anxiety in people under stressful conditions. The same authors stressed that longer-term and larger studies are needed before it could be justified as any kind of treatment.
One of the better-designed trials, published in Nutrients, gave 30 healthy adults 200 milligrams a day for four weeks in a placebo-controlled crossover design and reported better self-rated sleep quality and some improvement on cognitive tests. It was small, relied largely on questionnaires, and was supported by a company that sells the ingredient, so it should be read as a promising signal rather than proof. Other studies have found little difference. The honest summary is that the findings are interesting but limited and mixed, and they do not show that L-theanine manages any medical condition.
Getting it from tea
If you enjoy tea, you already consume some L-theanine. A few habits make the drink kinder to your day:
- Stop caffeinated tea by mid-afternoon if your sleep is light.
- Go easy on the sugar: a heavily sweetened glass several times a day adds up quickly.
- Drink tea between meals rather than with them if you have low iron. The NHS lists tea and coffee among the drinks that make it harder for the body to absorb iron.
- Try shaded green tea if you want a lighter cup than strong black tea.
Cautions and when to get help
L-theanine appears to be well tolerated by most healthy adults in the amounts studied, but long-term data are limited. Talk to a doctor or pharmacist first if you are pregnant or breastfeeding, take medicine for blood pressure, sedatives or any psychiatric medication, or have a chronic condition. Supplements should not be given to children without medical advice.
Feeling tense during an exam period or a heavy week at work is normal. Sleep, movement, daylight and talking to someone you trust come first. If worry, low mood or poor sleep last for weeks or get in the way of daily life, please see a doctor or mental health professional.
Sources
- The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review · Plant Foods for Human Nutrition
- Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial · Nutrients
- Iron deficiency anaemia · NHS
This article is general health information for educational purposes and is not medical advice. It does not promote any product. Talk to your doctor or pharmacist before starting a supplement, especially if you are pregnant, breastfeeding, have a health condition or take medication.