You may have heard tea is good for you, but you might not understand why. Tea has many compounds that make it healthy, but it's the antioxidants that give fruits and veggies a run for their money.
All true, non-herbal tea, including black, green, white, and oolong, comes from the Camellia sinensis plant. According to the Linus Pauling Institute (LPI), the way each variety is processed is what makes it unique. Different processing methods cause different levels of oxidation, which results in different tea varieties. Herbal "tea" is not tea by definition since it does not come from Camellia sinsensis but instead from various herbs and other botanicals.
Polyphenols and Flavonoids
All teas from Camellia sinensis contain antioxidant polyphenols. Antioxidants find and neutralize cell-damaging free radicals in the body. Much of tea's health benefits come from flavonoids, which are polyphenolic compounds that have antioxidant activity. However, according to LPI, flavonoids' most important contribution to health may be the ability to modulate cell-signaling pathways that regulate cell growth, proliferation, and death.
There are six subclasses of flavonoids: flavan-3-ols, anthocyanins, flavanones, flavones, flavonols, and isoflavones. Many are found in tea.
Flavonoid Content in Tea
Agricultural practices, environmental factors, ripening, storing, processing, and cooking all affect the flavonoid content in tea. This makes it difficult to determine flavonoid content at any given time; however, general amounts are available.
According to the USDA Database for the Flavonoid Content of Specific Foods and the USDA Database on the Isoflavone Content of Specific Foods, tea contains the following average levels of flavonoids. For each database, tea infusions were standardized to 1 gram tea leaves per 100 ml of boiling water.
|Black tea, brewed||118 mg||114 mg||0.00||4.0 mg||N/A|
|Green tea, brewed||138 mg||133 mg||0.30 mg||5.0 mg||.02 mg|
|White tea, brewed||69 mg||69 mg||N/A||N/A||N/A|
|Oolong tea, brewed||50 mg||50 mg||N/A||N/A||N/A|
Flavan-3-ols and Catechins
Flavan-3-ols are the highest source of flavonoids in tea. They include a powerful group of antioxidant compounds called catechins. According to the University of California Davis, catechins increase plasma antioxidant activity, aid in blood vessel expansion, and support fat oxidation (the breakdown of fatty acids to release energy).
UC Davis also points out that studies show tea catechins may help cardiovascular disease and improve mineral bone density. Despite positive study results, researchers aren't sure how catechins help cardiovascular disease. Studies on catechins for other diseases such as diabetes, Alzheimer's, and cancer show conflicting results. More studies are needed to prove efficacy.
Tannins are antioxidant polyphenols responsible for tea's bitter, astringent flavor. According to a review published in Critical Reviews in Food Science and Nutrition, some research showed tannins to be carcinogenic. However, later studies reported the carcinogenic activity may be due to "components associated with tannins rather than tannins themselves." In fact, tannins have shown anti-carcinogenic properties, possibly due to their antioxidant status, which helps prevent cell damage.
Tannin content in tea varies depending on how the tea is processed. Typically, the darker the tea and the longer it's brewed, the higher the tannin content.
Caffeine is known for giving tea its kick, but it also has antioxidant abilities. Research published in Medical Science Monitor shows caffeine and two compounds it breaks down into, theobromine and xanthine, have pro-oxidant and antioxidant properties. Results suggest caffeine may play a role in the ability of tea, as well as other foods and beverages that contain caffeine, to prevent disease.
How you prepare your tea is important. For example, if you load your morning cup of tea with sugar and milk or cream, it may negate health benefits. A study published in the International Journal of Food Science and Nutrition (IJFSN) found cow's milk reduced antioxidants in black tea; however, a later study showed adding milk has no effect.
The IJFSN study also discovered brewing tea in cooler temperatures reduces antioxidants as does brewing tea in tea bags instead of loose. For maximum antioxidant release, tea should be brewed at 90 degrees celsius (194 degrees Fahrenheit) for two minutes.
A Healthy Beverage Choice
The antioxidants in tea make it a healthy choice any time of day. John Weisburger, PhD, senior researcher at the Institute for Cancer Prevention, wrote in a WebMD article, green and black tea contain "eight to ten times the polyphenols in fruits and vegetables."
Despite its health benefits, drinking tea is not without risk. Tea contains caffeine, which is safe in moderation. However, Mayo Clinic reports caffeine may cause negative side effects in amounts over 400-500 mg per day. If you're sensitive to caffeine, choose decaffeinated tea. Decaffeination may reduce the antioxidants in tea, but you'll still get benefits.