Theine is found in tea leaf infusions. It's like caffeine but different... because there are polyphenols. Not a conclusive explanation. Yet today it's widely accepted in the French press. So what exactly is it?
Theine, caffeine: one and the same molecule...
Caffeine is an alkaloid (a molecule of plant origin that has a nitrogen atom) and is part of the family of methylxanthines. Caffeine has the formula 1,3,7-trimethylxanthine because of the number of hydrogens, their position and the number of methyl. This molecule was discovered in 1819 in coffee beans. A few years later, it was discovered in cocoa beans, mate and tea leaves. In each type of infusion, this methylxanthine took a particular name: theine for tea, caffeine for coffee. In pre-1900 publications, this nomenclature is predominant. (1)
And yet, by the end of the 1900s, it was already known that theine and caffeine were the same molecule. This distinction in terms probably allowed researchers to know what type of caffeine was referred to in the literature. Today, there are several newspaper articles that make it clear that theine and caffeine ... are caffeine. (2)
Caffeine and the body
Caffeine is a stimulant for the nervous system, heart rate and vasoconstriction of blood vessels. It binds to receptors on the surface of cells called adenosine receptors. There are 4 major subtypes (A1, A2a, A2b, A3) that will produce different effects. Among the most well known effects are an increase in blood pressure, heart rate and cognitive activity (arousal, memory). Health authorities recommend not to exceed 400 mg of caffeine per day, with variations according to age (2 mg/kg/day in children) and sex (2.4 mg/kg/day for women, 2 mg/kg/day for men). (3)
The absorption and elimination of caffeine is the same regardless of its source. Caffeine is absorbed in one hour in the small intestine. It also appears to be absorbed by the mammary gland and umbilical cord in pregnant women. The body will eliminate it thanks to oxidation enzymes in the liver. (4)
Yet despite this lack of difference, some say that coffee and tea do not produce the same effects: coffee would be very stimulating in a short time, tea would act more gently over time.
Caffeine effects of tea and coffee: a question of dose?
One of the main differences between coffee and tea is that brewed coffee contains between 2 and 4 times more caffeine than brewed tea per cup. (5) In 25cl of ground coffee (without information on the quantities of coffee used) there is on average between 90 and 133 mg of caffeine (6)(7). Conversely, the amount of caffeine in 25 cl of tea (without information on the amount of tea used) is between 45 and 53 mg, which is half the amount of caffeine in ground coffee (6)
There is a wide disparity in the data in the publications. The amounts of caffeine vary according to the origin of the product and its preparation. For coffee :
- 50cl of coffee from Guatemala would contain 172.7 mg of caffeine compared to 245.1 mg for a coffee from Costa Rica. (6)
- 25cl of instant coffee contains 93 mg of caffeine compared to 133 mg for a ground coffee (7)
The differences in caffeine levels are even more pronounced for tea. They will also depend on the tea plant used (cultivar), the tea family (green, black, etc), the manufacture of the leaves (broken leaves, etc) and the harvest period:
- By comparing 37 teas of different families (green, black, oolong, Pu'Erh, white) and different origins (China, India, Japan, etc.), Boros et al (8) showed differences in caffeine quantity ranging from 16.76 mg per gram of leaves (for green tea) to 19.31 mg per gram (for oolong tea). The amounts of caffeine in green tea appear to be higher in Japanese green tea crops (9)
- The same authors showed that broken leaf teas (Lipton Earl Grey tea bag, Pickwick green Melon tea bag) would release more caffeine than the averages evaluated (on average 4 mg more for tea bags) (8)
- A Taiwanese oolong tea with careful leaf processing such as Alishan contains only 10.96 mg per gram of leaves while a less processed Taiwanese oolong tea in a bag of the HWA Gung brand contains 39.71 mg per gram of leaves (i.e. for a 25 cl / 5g cup of tea more than the average ground coffee!). (9)
- Teas from Yunnan and Fuijian have different amounts of caffeine, with 14.56 mg per gram for Yunnan versus 16.20 mg per gram for Fujian. Green, black and Puerh teas all contained more than 20 mg/g of caffeine, showing that the data are very different from one publication to another. (10)
- Wakamatsu et al (11) demonstrated that the Japanese cultivar Yabukita produced green tea with 3 times more caffeine than green tea from the cultivar Benifuki.
- According to them, the fourth harvest of Benifuki tea would produce green teas with 1.5 to 2 times less caffeine (which is the case for Bancha (8) )
- The age of the tea plants would also have an impact on the amount of caffeine found in Jukro black tea. Mature tea plants would give a tea that is richer in caffeine after 40 and 60 days of growth compared to older tea plants 90 days after maturity. (12)
L-Theanine: an additional data in cup form
The amount of caffeine in tea is one explanation for a less pronounced effect of caffeine, but there is another: the molecular composition of tea.
In tea leaves, there is a molecule called L-theanine that is not found in coffee. It belongs to the family of amino acids, a class of molecules that help form proteins. The particularity of this amino acid is that it is not part of the composition of proteins and is present in plant cells such as those of tea leaves. Its quantity would be between 1 and 2% of the leaf mass, i.e. between 25 and 60 mg per cup of tea (13)
Although the mechanism of action of L-theanine is not known, it has caffeine-antagonistic effects: reduction of brain activity (14) (stress, improvement of sleep, etc.) and blood pressure (15)
A study of 44 adults who consumed 40 mg of caffeine and 97 mg of L-theanine showed that people who ingested L-theanine and caffeine had a slight increase in attention during concentration-demanding exercises even after 1 hour and 40 minutes (+5% attention) (16). While cardiac variations such as systolic and diastolic pressure were observed, there were no differences in heart rate. The magnitude of these effects would rather be due to the dose of caffeine, partially attenuated by the dose of L-theanine (17).
While there are as yet no studies that directly relate tea consumption to the body's levels of L-theanine and caffeine in tea, a plausible hypothesis is that L-theanine partially masks the effects of caffeine.
Theine does not exist: it is caffeine. The stimulating and relaxing effects of tea could be due to a lower concentration of caffeine compared to coffee and the presence of L-theanine having an inverse action to caffeine. Nevertheless, the quantities of these molecules are very different, depending on the tea leaves themselves and the way the tea is prepared. It is therefore necessary to carry out further research with these parameters in mind.
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