Tea Chemistry: Health & Caffeine
Throughout tea's history, it has been associated with significant health benefits beyond its delicious taste and aroma. Modern studies indicate that these healing properties may have a scientific basis, as consumption of tea appears to:
- Enhancing immune function
- Decrease LDL cholesterol levels/increase HDL cholesterol levels
- Lower blood pressure
- Lessen risk of heart attack
- Lower risk of stroke
- Reduce risk of cancer
- Boost longevity
- Enhance digestion
- Prevent dental cavities and gingivitis
- Lower stress levels
- Heighten mental attentiveness
It's important to note, however, that none of the research to date is conclusive. Furthermore, these studies often involve very different parameters, making it difficult to accurately compare results. In general, experiments tend to focus on three ingredients prominent in brewed tea: antioxidants (flavonoids), nutrients and caffeine.
Tea's health advantages seem to derive primarily from a high concentration of polyphenols (or organic compounds) called flavonoids, which have notable antioxidant properties. Antioxidants are thought to scavenge cell-damaging free radicals, impairing their ability to harm our bodies' beneficial molecules. While these compounds are naturally synthesized by all plants, Camellia sinensis stands out for its extensive range of flavonoids. Green tea contains the highest level of the flavonoid catechins, specifically EGCG (epigallocatechin gallate), which has been studied for its significant (and easily traceable) antioxidant effects. Overall, white and green teas—which are are only lightly or not oxidized—contain more catechins. As the leaf becomes increasingly oxidized, which occurs in oolong and black tea processing, these catechins are converted to other beneficial compounds called catechol tannins: theaflavins and thearubigins. It is these two antioxidant flavonoids that give oolong and black teas their darker leaf appearance, and liquor colors ranging from gold and red to dark brown and black. Note, in this USDA chart, black tea is the highest single source of flavonoids in the U.S. diet.
Tea is a dietary source of important vitamins and minerals. It contains carotene (a precursor to vitamin A), thiamine (vitamin B1), riboflavin (vitamin B2), ascorbic acid (vitamin C), vitamin E, folic acid, potassium, magnesium, manganese, and fluoride.
One of tea's greatest draws is the presence of caffeine, a powerful substance that awakens and revitalizes us throughout the day. This organic compound is extremely bitter when ingested alone, which helps the tea plant ward off insect attacks. In moderation, consumption of caffeine can be beneficial in stimulating the metabolism, increasing brain function and alertness.
Contrary to popular belief, caffeine levels do not correspond to general tea categories. For example, black tea does not contain more caffeine than green or white tea. Caffeine does occur in varying amounts in individual teas, and in different plant cultivars, stages of growth and parts of the plant. In general, a typical cup of coffee has approximately 125-185 milligrams of caffeine; the same size serving of tea, about half that amount. Note that these are typical levels: depending on how the tea is prepared, caffeine levels can vary greatly. Caffeine is water soluble, so the less time the leaves are infused or the lower the water temperature used, the less caffeine will be released.
The tenacity of caffeine is important to recognize: even through multiple infusions, tea leaves will continue to release notable amounts. We were once influenced by the common adage about removing most of the caffeine from any tea by a quick initial infusion in hot water, which would then be discarded. This has proven to not be the case. To address the issue in more depth, we invite you to read this article by the knowledgeable Nigel Melican, founder of Teacraft. It was initially published in the Cha Dao blog and parts of it are reprinted here with permission from the author and Cha Dao.
For those wishing to avoid any stimulating effects, it's best to consume only herbals, which are naturally caffeine-free. On the other hand, those seeking more of a boost can try matcha: as this style of powdered tea is consumed whole, it does contain significantly more caffeine than a regular infusion of tea leaves.
The effects of caffeine are complemented by another compound first found in tea, theophylline. While caffeine is primarily active in the brain and muscles, theophylline has general anti-inflammatory properties, and stimulates the respiratory system, heart and kidneys. This corresponds to research that tea is helpful in maintaining a healthy cardiovascular system.
What about decaf teas?
We find current decaffeinating methods yield teas flat and bland; the flavor, fragrance and all subtleties within the leaf disappear. Two processes are used for decaffeinating tea. One, which makes use of the solvent ethyl acetate, retains only 30% of the polyphenols. The other is a natural process that uses only water and carbon dioxide and is called effervescence. It retains 95% of the polyphenols.