Is Caffeine Your Cup of Tea? -- Part 2
In Part 1 of our discussion about tea & caffeine we reviewed several of the major factors that determine the caffeine content of tea including the location of the pluck, season of harvest, the varietal and cultivar, the manner of production and quality of the tea. We also pointed out that because of these factors white tea is considered to have the most caffeine while oolong tends to have the least.
In order to fully appreciate the difference between the caffeine in coffee and that in tea, one should understand just how caffeine works in the body. From the moment we wake up to the moment we go to sleep the neurons in our brains produce adenosine, a neuromodulator that regulates our sleep/wake cycles. The brain keeps tabs on the amount of adenosine in the body by use of adenosine receptors. As adenosine bonds with these receptors neural activity slows down, blood vessels in our brains dilate, the release of dopamine is inhibited and we become sleepy. Caffeine has a similar molecular structure as adenosine and actually mimics it by bonding to the adenosine receptors. In his book Buzz: The Science and Lore of Alcohol and Caffeine, Stephen Braun likens the power of caffeine to "putting a block of wood under one of the brain's primary brake pedals." With these adenosine receptors blocked by caffeine the brain doesn’t know to slow down so neural activity actually speeds up and the brain’s own stimulants, dopamine and glutamate, are free to do their thing. Dopamine is a neurotransmitter responsible for the way the brain regulates our movements. Without it we could not move at all. With too much of it we become jittery. In addition, dopamine is important for memory, problem solving and motivation. It is also one of the brain’s “feel good” chemical. It is released naturally as a reward for eating good food, having sex, etc. Without it we would have a total lack of motivation and enjoyment. Dopamine is responsible for caffeine’s addictive qualities. With the blockage of the adenosine receptors and the increase of neural activity, the pituitary gland secretes hormones that in turn cause the adrenal gland to produce adrenalin. Adrenalin causes the heart rate to increase along with blood pressure. And, finally, caffeine causes the blood vessels in the brain to constrict, which is why caffeine is considered a good headache remedy. When taken orally caffeine is completely absorbed and thoroughly distributed throughout the body within 45 minutes.
The caffeine in tea works in synergy with other components and it works differently than the caffeine in coffee, chocolate or energy drinks. Drink a cup of coffee, an energy drink or eat a chocolate bar and you get the full impact of the caffeine instantly, in one big rush……then you crash about 45 minutes later! Not so with tea. Tea is the only natural source of the amino acid L-theanine. L-Theanine, is a natural antidepressant and stress reliever. (Connoisseurs describe the taste of theanine as “umami”, or savory, fresh and lively. It is what gives tea the characteristic sweet taste that counters the astringency in tea. Theanine is also a flavor enhancer. It has a similar affect on the taste buds as monosodium glutamate (MSG.)) Theanine is a derivative of glutamine. As such, it has a small molecular size which allows it to cross the blood-brain barrier. It boosts alpha wave activity in the brain, promotes a relaxed state of concentration, reduces stress and improves mood. It does this by increasing the brain’s production of serotonin, dopamine and GABA, neurotransmitters that are associated with relaxation, sleep and the feeling of well-being. It allows one to maintain alertness, focused attention, and accuracy. L-theanine’s interaction with caffeine actually enhances performance in terms of attention switching and the ability to ignore distraction. It also modulates the more acute effects of higher doses of caffeine. That is to say, it will give you a six hour boost of sustainable, calm, focused energy without making you jittery or distracted. (The Buddhist monks knew this about tea centuries ago, though they probably did not know that L-theanine was responsible.) An added bonus is that L-Theanine also enhances the immune system and lowers blood pressure. And for those of you who are sensitive to caffeine, L-Theanine actually counteracts the harmful side effects of caffeine. Within 20 to 30 minutes of drinking a cup of tea it will calm you down and lower your heart rate and blood pressure. The caffeine in tea is trapped, so to speak, in the polyphenols and theanine and is released progressively. It takes approximately ten hours for the caffeine in tea to be released into the body as opposed to the 45 minutes it takes with coffee.
Recent studies have also shown that caffeine works in synergy with polyphenols in tea. The most potent polyphenol in tea is EGCG (epigallocatechin 3 gallate.) It is recognized especially for its anti-oxidative, anti-mutagenic and anti-pathogenic properties. A 2006 study published in the Journal of the American College of Nutrition found that the caffeine in tea bonds with EGCG to form larger particles, and that working together they are more effective in their preventive functions than they are when working alone.
In Part 1 of this article we mentioned that the quality of tea is important. Major factors determining the quality of tea are the location of the pluck (the top two leaves and the bud are the highest quality,) the manner of production and the handling both during production and after. Tea catechins are very unstable and their composition can easily by compromised by mishandling and exposure to the environment. The more broken the leaves the faster they degrade. The first growth of the season--as soon as the plant comes out of dormancy—has the highest caffeine content. That would be the top two leaves and the bud. However, those are also the leaves that contain the highest concentration of polyphenols, including EGCG. The farther down the stalk you go the lower the concentration. A USDA report showed some high grade loose leaf teas (using 1 g of leaves to 100 ml of water) contained as much as 200 mg of EGCG alone in each 100 ml of tea liquor compared to some lower grades with only 2.3 mg. The same goes for l-theanine—the higher quality the tea the more l-theanine it has. A recent study by Korean scientists found that a premium quality green tea or high grown oolong tea could contain as much as 3200 mg of l-theanine compared to 800 for a low grade loose leaf tea and zero for tea bag tea powder. So, while you may be getting a little more caffeine in the higher grade teas (perhaps 15 to 20 mg more,) you are getting significantly more EGCG and l-theanine.
Just to put things in perspective, in Part 3 we will take a look at how much caffeine there is in tea compared to other popular food, beverages and over the counter pills and how much caffeine is safe. We will also provide some insight into how to choose a tea that is lower in caffeine.