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!
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]
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.
The contents of this website are for information purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.