Tolerance to theine: what side effects?

The caffeine works by blocking the receptors ofadenosine, a molecule that signals fatigue to the brain. The word “theine” is a historical legacy, as the substance was isolated separately in tea in the 19th century before being identified as identical.

In tea, caffeine binds partially to tannins. Its release into the body is therefore more gradual, which explains the longer-lasting and less abrupt effect described by many drinkers.

The L-Theanine is an amino acid found almost exclusively in the tea plant. Several studies referenced on PubMed show that it promotes alpha brain waves, associated with a state of calm alertness.

Combined with caffeine, it produces alertness without nervousness. Shade-grown teas such as gyokuro and Matcha contain the most, because shading slows the conversion of theanine into catechins.

Tolerance varies according to weight, genetics, and habit. The most common signs of excessive intake:

• nervousness, palpitations, trembling hands;
• sleep that is shorter or lighter;
• digestive discomfort on an empty stomach, linked to tannins andEGCG;
• headaches when stopping suddenly after heavy consumption.

The EFSA considers that a healthy adult can consume up to 400 mg of caffeine per day, equivalent to eight to ten average cups of tea. Most people feel the effects well before that.

The polyphenols reduce the absorption of plant-based iron when tea is drunk during a meal, as several studies on PubMed remind us. For people with a deficiency, simply delay the cup by one hour.

Practical levers:

• lower the temperature: less caffeine extracted;
• shorten the infusion: caffeine is released mainly in the first two minutes;
• choose the family: a white tea or a green tea light rather than a black tea full-bodied;
• avoid tea six hours before bedtime if your sleep is sensitive.

Theoxidation does not determine caffeine content on its own: a white tea of buds can contain as much as a black tea. It is the cultivar and the part of the plant harvested that matter most.

The rate at which caffeine is eliminated depends largely on the liver enzyme CYP1A2. Depending on genetic variants, some people eliminate half the caffeine in three hours, others in seven or more. Smoking speeds up this metabolism, while pregnancy and certain medications slow it down.

Habit also plays a role: regular consumption increases the number of receptors foradenosine, which reduces the perceived effect. This is known as tolerance. Stopping abruptly then causes fatigue and headaches for a few days.

To reduce consumption without discomfort, it is better to cut back gradually: one cup fewer every three or four days, or replacing a cup of black tea with a white tea light one.

Approximate ranges for 200 ml, varying greatly depending on the cultivar, the harvest and thetime:

• Matcha: 60 to 80 mg, since the powder is consumed;
• black tea: 40 to 60 mg;
• oolong: 30 to 50 mg;
• green tea: 20 to 40 mg;
• hojicha and bancha: 10 to 20 mg;
• rooibos and herbal teas: 0 mg.

These figures show that no family is « caffeine-free » apart from herbal teas. But they also remind us that a cup of tea contains, on average, half as much caffeine as filter coffee. The liquor can then be adjusted through the quantity of leaves, the temperature and the duration oftime.

At HOLLIN taste counter, our contemporary Asian grocery store in Sartrouville, we guide you according to your sensitivity: teas rich in L-theanine for concentration, natural infusions and scented teas for the evening. A conversation is often enough to readjust a routine.

Dian VAULTIER, for HOLLIN.