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.

Antioxidant Flavonoids

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 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 the 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.


What Are the Best Teas for Health?

It’s likely that we all enjoy a hot cup of tea — or herbal infusion — at least from time to time, if not on a daily basis. But what are the most important health benefits that some of these soothing teas can bring us?

“Tea began as a medicine and grew into a beverage,” writes 19th-century Japanese scholar Okakura Kakuzo in his infamous publication The Book of Tea.

In it, he speaks at length about the history of tea and the philosophy of the traditional Japanese tea ceremony.

Kakuzo was correct: modern research about the history of tea-drinking in the world confirms that this beverage was originally consumed less for pleasure or as a mindfulness aid, calling for the drinker to take slow sips and be in the moment.

Instead, as shown by Prof. Victor Henry Mair — from the University of Pennsylvania in Philadelphia — in The True History of Tea, early in its history, the tea plant (Camellia sinensis) became popular for its medicinal properties.

The tea plant’s main varieties — Camellia sinensis sinensis and Camellia sinensis assamica — are responsible for most of the tea brews that we are accustomed to black tea, green tea, white tea, and oolong tea.

There are many other types of teas and infusions using various other plants, such as Aspalathus linearis, which is better known as “rooibos” or “red bush.” In this Spotlight, we’ll give you an overview of the top five teas that can benefit your health.

1. Green tea

A favorite with tea drinkers everywhere, green tea has been praised for its medicinal properties for years. Some recent studies have now confirmed some of these benefits, suggesting that green tea may protect various aspects of our health.

pot and cups of green tea

Green tea can increase cognitive functioning.

To begin with, this beverage has been found to enhance cognitive functioning, with one study connecting it to better working memory, the type of we use on a day-to-day basis.

Researchers from the University Hospital of Basel in Switzerland found that healthy people who agreed to consume a soft drink containing 27.5 grams of green tea extract exhibited more intense activity in brain areas linked to working memory.

Therefore, participants who had ingested the green tea extract had better connectivity between the frontal and parietal lobes of the brain, which are two regions involved in aspects of learning, memory processes, and decision-making.

The health benefits brought about by green tea have been linked with their content of polyphenols, which are micronutrients with antioxidant properties. As antioxidants, these substances can protect against the action of free radicals, which induce the type of cellular damage consistent with aging.

A 2017 study that was published in the Journal of the American Chemical Society found that one such polyphenol found in green tea — called epigallocatechin gallate — may lower the risk of Alzheimer’s disease by interacting with the “building blocks” that form beta-amyloid plaques.

A buildup of these plaques in the brain is typical of this condition and impairs brain cell signaling. Epigallocatechin gallate, this study suggests, could stop beta-amyloid from forming into plaques, potentially helping to keep Alzheimer’s at bay.

This same green tea polyphenol has also been said to slow down the growth of tumor cells of certain types of cancer, such as pancreatic cancer.

Research that was led by the Los Angeles Biomedical Research Institute in California has shown that epigallocatechin gallate can disrupt the metabolism of pancreatic cancer cells, thereby impairing their growth.

2. Jasmine tea

What we refer to as “jasmine tea” is a type of beverage that usually has green tea at its base, to which jasmine flowers are added for an enriched aroma.

cup of tea with jasmine flower

Jasmine tea is an important component of the diet of one of the longest-living populations in the world.

But the benefits of jasmine tea aren’t solely due to the antioxidant effects of the tea plant since jasmine blooms also bring their own medicinal properties to the mix.

In the book Ikigai: The Japanese Secret to a Long and Happy Life, authors Héctor García and Francesc Miralles note that the inhabitants of a healthy, long-lived community in the Okinawa Prefecture of Japan are avid drinkers of Sanpin-cha, a special blend of green tea and jasmine.

“Okinawans drink more Sanpin-cha — a mix of green tea and jasmine flowers — than any other kind of tea,” they write, suggesting that this blend may play a role in keeping the inhabitants of Okinawa healthy and mentally agile well into old age. This may be because, like the tea plant, jasmine flowers contain antioxidants — which may protect cells from age-related damage.

Jasmine itself has been linked to improved physical well-being and is said to reduce the impact of stress. That is why some researchers have experimented with compounds derived from this plant in the search of better therapies.

For instance, Prof. Eliezer Flescher — from Tel Aviv University in Israel — noticed that methyl jasmonate, which is a compound obtained from jasmonic acid, found in the jasmine plant, induces the death of cervical cancer cells.

And, if you happen to enjoy drinking jasmine tea simply because you love the way it smells, there’s actually a good reason for that. Research that was published in the European Journal of Applied Physiology explained that the smell of jasmine tea is soothing, able to calm nerves, and able to help regulate mood.

3. Rooibos tea

Another type of tea with antioxidant properties is rooibos, or “redbush tea,” which is prepared from the Aspalathus linearis plant native to South Africa.

rooibos tea

Rooibos tea may protect liver health.

Research has suggested that the antioxidant effects of rooibos are similar to, if not quite as strong as, those of green tea.

A recent study on the rat model has suggested that the antioxidants in rooibos tea may protect the liver from oxidative stress, helping to render this organ more resilient to induced damage.

The researchers who conducted the study noted that their findings suggest that rooibos tea or rooibos-derived dietary supplements may offer a useful health boost.

Results from this study suggest that the daily intake of unfermented rooibos herbal tea or a derived commercial rooibos supplement may benefit human health by providing the liver with an enhanced antioxidant capacity to reduce damage induced by toxicants.”

Moreover, rooibos has also been cited as helpful in lowering blood pressure and relaxing tense muscles, suggesting that the active ingredient in this instance might be one of the flavonoids (pigments) that it contains: chrysoeriol.

Unlike green or black tea, rooibos does not contain any caffeine so it won’t have the same stimulating effects. This makes it safe to drink well into the evening.

4. Hibiscus tea

Those of you who enjoy the refreshing taste of a more sour brew may also be familiar with herbal infusions of hibiscus, a plant whose flowers can be used not just to make invigorating beverages, but also to give a subtle “punch” to salads, or as an elegant garnish for sophisticated dishes.

hibiscus tea

Hibiscus tea is an antioxidant and may bring cardiovascular benefits.

The most commonly used variety is Hibiscus sabdariffa, also known as the “roselle.”

For the tea — or, more correctly “tisane” (herbal tea) — its calyces are typically used, although other parts of the plant, such as the leaves, seeds, and roots, are safe for consumption.

Studies have suggested that extracts from the hibiscus calyx and hibiscus leaves have antioxidant and antitumoral effects.

Therefore, they may protect against the aging action of free radicals at a cellular level, as well as fight certain types of leukemia cells.

Hibiscus tea has also been tied to cardiovascular benefits, helping to regulate systolic and diastolic blood pressure — that is, blood pressure during and in-between heartbeats, respectively.

Though not so commonly used to brew tea, hibiscus leaves have also been linked repeatedly to a wide array of health benefits. Thus, the polyphenols in hibiscus leaves may help to induce tumor cell death in skin cancer, according to a 2015 study.

Another study from the same year also argued that hibiscus leaf extracts could inhibit the action of prostate cancer cells.

5. Lemon verbena tea

Another herbal tea whose medicinal properties are getting increasingly recognized is that made out of lemon verbena, scientifically dubbed Aloysia citrodora.

dried lemon verbena

Infusions with lemon verbena are said to help with weight management.

It is the citrus-flavored cousin of a better-known plant that has been used in herbal infusions for years: verbena, or vervain (Verbena Officinalis).

Infusions made with lemon verbena are great for those who, like me, prefer a subtler citrusy aroma in their hot drinks, rather than the strong, lemony flavor of commonly commercialized citrus tea blends.

The first time that I came upon this plant sold as a tisane herb was in a local organic shop that was selling it as “weight loss tea.”

In fact, studies have shown that the polyphenols in this plant can decrease the formation of fatty acids, marking its potential use in the treatment of obesity-related health issues.

Researchers have also suggested that lemon verbena extracts may help to lower inflammatory markers’ levels in the blood of some people with multiple sclerosis.

“Results demonstrate that supplementation with lemon verbena extracts may affect the cytokine [inflammation markers] profile depending on the clinical subtype,” the study authors conclude.

Having a cup of your tea — or tisane — of choice may be a pleasant way to carve out some self-indulgence time and stimulate your bodily and mental well-being in a subtle way.

But always keep in mind that, as the saying goes, “one swallow does not a summer make,” and the most potent health benefits are best reaped by leading a healthful, wholesome lifestyle.

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