Tea is the most popular beverage in the world after water. It’s a simple preparation of pouring hot water over cured leaves of the Camellia sinensis plant. The first recording of tea described it as a medicinal beverage in China in the 3rd century AD. Merchants helped its popularity to spread quickly across continents. In the early 19th century, Great Britain popularized the concept of afternoon tea, a break from one’s routine in which tea is served alongside sandwiches and baked goods such as scones. The flavor of tea varies by where the tea leaves are harvested and how they are grown and processed. Black tea is the most popular worldwide, followed by green, oolong, and white tea. 
Herbal teas are not made from the Camellia plant but from dried herbs, spices, flowers, fruit, seeds, roots, or leaves of other plants; they do not typically contain caffeine as do traditional teas.
- Caffeine (traditional teas, not herbal)
- Flavonols – myricetin, quercetin, kaempferol
- Theaflavins – formed when black tea leaves are oxidized
- Catechins – found in green tea; epigallocatechin-3 gallate (EGCG) is the main form
Most traditional teas do not contain a significant amount of nutrients, but are rich in polyphenols. These are plant chemicals that give teas their distinct flavor and aroma and may have health-promoting properties.
Tea and Health
Animal studies suggest potential health benefits of tea due to its high polyphenol content. Human studies have generally been less conclusive, yet show promise. Observational research has found that tea consumption of 2-3 cups daily is associated with a reduced risk of premature death, heart disease, stroke, and type 2 diabetes.  However, there may be an increased risk of esophageal and stomach cancers from drinking tea that is too hot (130-140° F). [2,3] Randomized controlled trials are needed to confirm if these healthful and harmful associations are causal. In the meantime, there appears to be little risk associated with drinking tea except for frequent consumption of very hot tea. So pick a color, let it cool, and enjoy a cup!
Is decaffeinated tea healthy?
Decaffeinated tea is an option if you enjoy the flavor and experience of tea but are sensitive to caffeine. People have varying sensitivity to caffeine but it is classified as a stimulant that has the potential to affect the nervous system and heart rate, and cause jitteriness. In general, traditional teas already have about half the caffeine of coffee and even less if the brewing time is shorter.
To decaffeinate tea, there are different methods. One process uses an organic chemical solvent (either ethyl acetate or methylene chloride) that also removes most of tea’s polyphenols. The residual amount of the chemical after processing is minimal to none, and no research has shown negative health effects. Another method called “effervescence” uses water and carbon dioxide, which retains the majority of polyphenols. Both methods apply the chemical or gas onto moistened tea leaves, which bonds to the caffeine; when the leaves are dried, the caffeine evaporates along with the solvent/gas. If you wish to know which processing method is used, check the package label or contact the manufacturer.
Herbal teas are naturally caffeine-free and do not undergo a decaffeination process.
Most research looks at the health effects of traditional teas, not decaffeinated. Decaffeinated tea may lose polyphenols that are associated with health benefits, depending on the processing method. Polyphenol content varies widely among teas even before the decaffeinated process, so it is hard to know the exact amount that remains. Regardless of decaffeination type, tea is still considered a healthful beverage choice.
Spotlight on tea and antioxidants
Polyphenols, or flavonoids, are likely a key component to what makes tea a healthful drink. These chemical compounds act as antioxidants, which control the damaging effects of free radicals in the body. Free radicals can alter DNA by stealing its electrons, and this mutated DNA can increase LDL cholesterol or alter cell membrane traffic—both harmful to our health. Though green tea is often believed to be richer in polyphenols than black or oolong (red) teas, studies show that—with the exception of decaffeinated tea—all plain teas have about the same levels of these chemicals, albeit in different proportions. Green tea is richest in epigallocatechin-3 gallate whereas black tea is richest in theaflavins; research has shown that both can exert health benefits. Herbal teas contain polyphenols as well but will vary highly depending on its plant origin.
Indeed, one reason for conflicting results in observational studies may be the wide variations in tea types with varying flavonoid content.  Where the tea leaves are grown, the specific blend of tea leaves, type of processing, and addition of ingredients such as milk, honey, and lemon can alter specific flavonoid content. How accurately people report their tea intake (e.g., type, amount, brew strength) and their overall diet (e.g., do they eat other foods rich in flavonoids?) are other factors that need to be clarified as they can affect study results. For example:
- Some research suggests that the protein and possibly the fat in milk may reduce the antioxidant capacity of tea.  Flavonoids are known to “deactivate” when binding to proteins so this theory makes scientific sense. 
- One study that analyzed the effects of adding skimmed, semi-skimmed, and whole milk to tea concluded that skimmed milk significantly reduced the antioxidant capacity of tea. Higher-fat milks also reduced the antioxidant capacity of tea, but to a lesser degree.  All said, in practice it’s important to keep in mind that tea—even tea with a splash of milk—can be a healthful drink.
A Cochrane review found very few large, long-term studies that examined green or black tea for the primary prevention of cardiovascular disease. The authors noted that tea appears to show favorable effects on cardiovascular risk factors based on the available evidence, but this is based on only a modest number of small, short-term clinical trials so firm conclusions cannot be made. 
- Stroke and mortality—Polyphenols, the antioxidants abundant in tea, have been shown to reduce the risk of death due to cardiovascular disease,  including stroke. [7,10] In one study of 77,000 Japanese men and women, green tea and oolong tea consumption was linked with lower risk of death from cardiovascular disease.  Another cohort of 82,369 Japanese men and women followed for an average of 13 years found that those who drank 2-3 cups of green tea daily had a 14% reduced risk of stroke, and drinking 4 or more cups daily was associated with a 20% reduced risk.  Other large-scale studies show that black tea may contribute to heart health,  with research suggesting that drinking at least 3 cups of either black or green tea a day appears to reduce the risk of stroke by 21%. 
- High blood pressure—Tea flavonoids may help to keep the lining of blood vessels smooth and elastic. In a study of green and oolong tea consumption, regular consumption for one year reduced the risk of developing hypertension.  Long-term regular consumption of black tea has also been shown to lower blood pressure.  A meta-analysis that combined the results of 14 randomized controlled trials found that green tea extracts produced a small reduction in blood pressure in overweight and obese adults, though the authors noted that the trials included a small number of participants and therefore strong conclusions could not be drawn. 
- Cholesterol—Tea flavonoids have antioxidant properties that may prevent the oxidation of LDL cholesterol particles that could lead to inflammation and hardening of arteries. However, there is still a lack of consistent evidence in human studies showing a benefit. A meta-analysis of 15 randomized controlled trials found no significant effect of black tea on cholesterol levels (including total cholesterol, LDL and cholesterol) in both healthy subjects and people with coronary artery disease.  Two separate meta-analyses of randomized controlled trials looking at tea intake and cholesterol levels found that both black and green tea lowered LDL blood cholesterol levels (as measured in milligrams per decileter [mg/dL]). With green tea consumption, fasting total cholesterol and LDL cholesterol was significantly lowered by 7 mg/dL and 2 mg/dL, respectively. Black tea reduced LDL cholesterol by almost 5 mg/dL. However, the authors acknowledged that most of the studies included were of low quality, with short study durations and a small number of participants. [19,20]
Epigallocatechin-3-gallate (EGCG) in green tea has been shown in animal and cell studies to prevent the growth of cancer cells and cause them to die.  Green and black tea extracts have been shown in animal studies to reduce the risk or delay the progression of cancer.  Green tea might also have a positive effect in reducing risk of breast, ovarian, prostate, and endometrial cancers, though evidence is limited.  A meta-analysis of 41 prospective studies found no decreased risk of five cancers (breast, colorectal, liver, prostate, stomach) with black tea intake (about 3 cups daily).  Overall, human studies about tea and cancer are limited and results are inconsistent. Learn more about cancer and antioxidants.
A positive association has been found between drinking hot tea and a greater risk of esophageal cancer. It is believed that very hot beverages may cause cell injury that could lead to cancer.  Studies showing this association with tea have been largely in Asia and the Middle East. There is less evidence in Western populations, where beverages including coffee and tea are usually consumed at more moderate temperatures. Westerners also may add milk or cream to very hot beverages, immediately lowering the temperature. A meta-analysis of 16 case-control studies conducted in China, India, Iran and other countries in Europe and South America found an association of increased risk of esophageal cancer with higher consumption of both very hot beverages and foods.  It appears that cancer risk of this type is directly linked to temperature, rather than a specific component of the food or beverage.
A large prospective study of 50,045 Iranian men and women followed for about 10 years found a 90% increased risk of esophageal cancer when comparing those drinking “very hot” versus “cold/lukewarm” tea. It also found that the shorter the time from pouring the tea into a cup to drinking it was associated with increased risk. In May 2016, after a review of available research, the International Agency for Research on Cancer (IARC) concluded that “drinking very hot beverages above 65 C (140 F)” is “probably carcinogenic.”  They acknowledged certain limitations of existing studies that precluded listing a “carcinogenic” label, one being that data on the actual temperature of tea are self-reported, in which the perception of “hot” may vary among ethnicities and populations.
In 2018, a large cohort study of 456,155 men and women in China followed for a median of nine years found that participants who drank burning-hot tea daily along with excessive alcohol had five times the risk of developing esophageal cancer than those who drank less of both beverages. Those who drank burning-hot tea daily and smoked tobacco had double the risk of developing this cancer. 
There are five elements to avoid to keep tea as fresh as possible: light, heat, moisture, odor, and air. Tea bags should be stored in their original container or placed in a sealed plastic bin. Loose-leaf teas should be stored in an airtight container. Place all teas in a dark cupboard at a consistent room temperature. Tea tends to absorb odors from food and even other strongly scented teas, so keep them separate. Freezing and refrigerating is not recommended as the moisture introduced can degrade the tea.
If unopened, tea will last about one year beyond the “best by” date. After opening, packaged and loose-leaf teas last about one year. However, some black and oolong teas can last up to two years, and more delicate teas may last only 6 months. The flavor is your best guide to determining how long to keep a tea in your cupboard.
Avoid purchasing expensive bottled teas or teas from shops that contain added sweeteners. To enjoy the maximum benefits of drinking tea, consider brewing your own at home. You can serve it hot, or make a pitcher of home-brewed iced tea during warmer months.
Black and oolong teas are generally steeped in hot or boiling water (about 210º F) and brewed for about 4-5 minutes. Green tea is steeped at a slightly lower temperature 180º F from 4-15 minutes. The longer tea steeps, the stronger the flavor with bitter notes.
Additives of sugar, cream, or milk can reduce the polyphenol content of tea. For the greatest health benefits, try serving tea plain or without too many additives. A dash of vanilla or cinnamon can mimic sweetness. Some fruit-flavored herbal teas taste naturally sweet to the palate without added sweeteners.
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