Tea is a beverage made from processed tea leaves and hot or boiling water. The four major types of tea (black, oolong, green and white) are considered functional foods because they naturally contain chemicals associated with certain health benefits. Each type of tea contains tannins, including catechins, which act as antioxidants in the body, helping to prevent cellular damage. Tea also naturally contains caffeine, which acts as a stimulant in the body.

Each type of tea is made from the same plant, but differs in how they are processed. Processing differences result in varying tastes and level of antioxidants among the types. Black tea contains the least amount of antioxidants and white tea the most. In addition, tea that is brewed (rather than instant) and steeped for longer periods of time in hot water may contain more antioxidants.  

Moderate amounts of tea are considered safe for most people. However, it is not known how much tea should be consumed in order to gain its associated health benefits. Components in tea may interact with certain medications, medical conditions or stages of life, other foods or supplements. The caffeine in tea may cause gastrointestinal problems and insomnia. Caffeine is also habit-forming and may cause withdrawal symptoms if use is suddenly discontinued.

Herbal teas are made from herbs or plants other than the tea plant. Thus, they contain no tea and are sometimes referred to as herbal infusion or tisane. The safety and effectiveness of most herbs has not been scientifically proven. Problems may arise when herbal teas are consumed excessively, consumed to treat medical conditions or when unsafe herbs are consumed.

Tea extracts may be available in supplement form. However, there is a lack of well-designed scientific studies concerning the safety and effectiveness of tea supplements. In addition, adverse side effects have occurred with tea supplements. Most nutrition experts recommend getting nutrients and other healthy substances from foods rather than relying on supplements.

The U.S. Food and Drug Administration (FDA) has not approved any health claims associating tea use with any disease or medical condition. However, other types of claims (e.g., structure-function claims, nutrient content claims) may be allowed.

Marketers of herbal teas may avoid making health claims by including language such as “relaxing” or “soothing” on their labels. Consumers are advised to carefully read product labels before purchasing teas or herbal products, and to consult their physician or registered dietitian if they have doubts about whether a product is appropriate for use. 

Tea is a beverage made by soaking tea leaves in hot or boiling water. The resulting drink is often aromatic, pleasant and may be considered soothing. Its taste can vary and may be slightly bitter or astringent. Tea may be consumed in a number of ways. It is often enhanced with milk, sugar, honey or lemon. It may be consumed right away (while hot), or when cold. Iced tea is more popular than hot tea in the United States, with ready-to-drink varieties being consumed most often.  

Tea comes from the tea plant (Camellia sinensis), a large evergreen shrub with white flowers. This plant is sometimes also referred to as Thea sinensis. In the wild, the tea plant usually grows to more than 26 feet (8 meters) tall. However, when commercially cultivated, it is often trimmed to just under 5 feet (1.5 meters) for ease in harvesting. India, China, Sri Lanka, Kenya, Indonesia and Argentina are the major global producers of tea.

Only the leaves of the tea plant are used to make tea. There is little to no nutritional value in tea, although tea may contain minute amounts of some vitamins and minerals (e.g., folate, iron).

Despite the lack of specific nutrients, tea is considered a functional food because its leaves naturally contain a number of substances associated with certain health benefits. This primarily includes tannins and a type of phytochemical called catechins. These chemicals act as antioxidants in the body, protecting cells from being damaged by free radicals. Antioxidants are associated with reduced risks of some cancers and cardiovascular disease.

More antioxidants are available when tea is brewed (e.g., 541 to 692 micrograms [mcg] in an 8-ounce serving), than in instant tea products (e.g., 122 to 312 mcg in 8 ounces). Steeping tea for longer periods of time may release more catechins into the preparation.

Antioxidant levels may also differ, depending on the way the tea leaves are processed.

There are several steps to processing tea leaves:

• Picking. This removes the leaves from the tea plant.
  
  
• Rolling. This releases the enzymes and juices that give the tea its aroma and taste.
  
  
• Drying. This is performed to remove excess moisture.
  
  
• Heating. Interrupts or halts the oxidation process.
  
  
• Flavoring. Different flavors, herbs or other ingredients may be added.  

The primary difference in processing involves oxidation, a natural chemical reaction due to oxygen exposure. When oxidization occurs, the composition of phytochemicals in the tea leaves change. In general, the more oxidation the tea leaves are exposed to, the fewer antioxidants the tea contains.

Oxidation is interrupted or halted through heating. This may be done by stirring tea leaves in heated pans, steaming the leaves or heating them in ovens. Oxidation may begin at any time after the leaf is picked, so timing and order of the processing steps is crucial to determining the type of tea (e.g., black, oolong, green, white) as well as its flavor and level of antioxidants. For example, black tea is completely oxidized, oolong is partially oxidized, green tea is minimally oxidized, and white tea is not oxidized at all. Thus, they have respectively increasing levels of antioxidants as a result.

There are four major types of tea, which are all made from the same plant, Camellia sinensis, a white-flowering evergreen shrub. Although the color of the teas may differ (and correspond to their respective names), the different types are the result of processing. This also affects the flavor and amount of antioxidants each contains. See About Tea for more information.

The four major types of tea are:

• Black tea. Leaves are allowed to completely oxidize during processing, producing a strong flavor with high levels of caffeine. This type of tea has the least amount of catechins (type of phytochemical associated with certain health benefits) due to the more extensive processing. In the Western world, black tea is named for the color of the tea leaves. In China, it is sometimes called red tea for the color of the liquid produced. Most tea consumed in the United States is black tea.
  
  
• Oolong tea. Leaves are partially oxidized during processing. They are usually allowed to oxidize for two to three days, and then the oxidization process is interrupted before it is completed. The amount of processing of leaves falls between that required for black and green teas, although the taste of oolong is more similar to green tea.
  
  
• Green tea. Minimal oxidation occurs, usually through steaming or dry cooking in hot pans. Green tea is usually processed within a couple days of being picked and made from mature tea leaves. Green tea has more antioxidants than black and oolong teas, but less than white tea. It is gaining popularity in the United States.
  
  
• White tea. Made from young leaves that have not turned green (they are sometimes shaded from the sun). Leaves are steamed and dried almost immediately after being picked, and no oxidation is allowed to occur. White tea has the highest level of antioxidants of the four teas. This type of tea is expensive and uncommon outside of China.

Each type of tea may be available with added flavors, herbs or other ingredients (e.g., chamomile, rosehip). For example, Earl Grey tea is a popular blend of black tea and oil of bergamot (orange flavored oil). These flavored varieties are still considered tea as long as they are made from the tea plant.   

Tea may be identified by various names, often according to its location of origin. For example, Ceylon tea is grown in Sri Lanka (formerly known as Ceylon), Yunnan and Lapsang Souchong in China, and Darjeeling in India. India and Sri Lanka have primarily been known for producing black tea, while China has produced most of the oolong and green varieties. However, many countries that typically produced only one type of tea are now producing a variety of types. Thus, Darjeeling or Ceylon teas may be black, green or oolong. 

Herbal tea, sometimes called an herbal infusion or tisane, is made from plants other than the tea plant and, thus, contains no tea. Some herbal teas may contain antioxidants, but not necessarily in the quantity available in products made from the tea plant. For example, tea made from plant Aspalathus linearis (also known as red bush or rooibos), which is native to South Africa, has been gaining popularity in the United States and may also contain antioxidants. Herbal teas are required by the U.S. Food and Drug Administration (FDA) to identify on their labels the name of the plant from which they are made.

There are a great variety of herbal teas. Many are promoted as being associated with certain health benefits. However, the safety and effectiveness of most herbs has not been proven.

Tea is considered safe for most adults when it is consumed in moderation.

Tea is a natural source of catechins, a type of flavonoid phytochemical. Catechins act as antioxidants in the body and are associated with reduced risks of cancer, stroke and cardiovascular disease, as well possibly helping limit the effects of aging. Tea also contains antioxidants such as tannins and possibly anthocyanins. There are four main catechin substances: catechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC) and epigallocatechin gallate (EGCG).

Research regarding the effects of catechins in humans is not conclusive. Results have been mixed, possibly due to variances in people’s diets, environments and population differences (e.g., gender, age, genetic factors). In addition, it is unknown what amount of catechins is needed to received the potential associated health benefits.

There are many ongoing studies examining the possible benefits of drinking tea. Recently, researchers have found possible evidence of certain potential benefits. Many of these studies have investigated the potential health benefits of green tea.

For example, one study found that a compound derived from green tea may help protect the body against developing HIV-associated dementia (AIDS dementia complex). Another study found that a different compound derived from green tea may help suppress factors that lead to destruction of cartilage and bone associated with arthritis. Studies have also indicated that green tea may protect the body against autoimmune disease, and that it may even protect against the ravages of illnesses such as cardiovascular disease.

Other studies have found the following possible benefits:

• Drinking two cups of spearmint tea a day for five days may reduce levels of “masculinizing” androgen hormones in women with hirsutism.

• Consuming tea extracts may reduce inflammation in patients with skin damaged during radiation treatment for cancer.

• Drinking black tea daily may have a calming effect on stress hormones in the body.

Other studies have failed to find a strong link between tea and potential health benefits. For example, researchers in one study concluded that drinking tea does not lower blood pressure.

While consumption of tea is associated with possible health benefits, tea use may also have adverse effects. Components of tea may also interfere with certain medications (e.g., anticoagulants) and make them less effective. Tea may also decrease the absorption of non-heme sources (plant) of iron. Finally, certain foods (e.g., extensive fiber intake) may inhibit the absorption of phytochemicals in tea, potentially lessening its healthful effects.

Recent studies have also found other potential negative health consequences associated with drinking tea. For example, drinking products that contain lavender oil and tea tree oil may cause enlarged breast tissue in pre-pubescent boys.

Leaves from the tea plant also naturally contain caffeine, which has a stimulant effect on the body. Caffeine affects the central nervous system and may result in temporary alertness and a decreased desire for sleep. Some research has indicated the tannins in tea may also protect against cavities, although results are not clear and more study is needed. Tea also contains two related substances, theobromine and theophylline, which act similarly to caffeine. 

Examples of the caffeine content of various caffeinated beverages include:

Moderate consumption of caffeine does not appear to increase health risks. However, it may irritate the stomach. People sensitive to the effects of caffeine (e.g., people with a small body mass, a short history of caffeine use or under high levels of stress) may experience gastrointestinal problems when drinking tea. The caffeine in tea may also cause insomnia, anxiety, irritability, nausea and diarrhea. In large amounts, it may cause seizures and abnormal heart rhythms.

Caffeine may be habit-forming and can result in withdrawal symptoms if consumed regularly and then stopped. In addition, certain medications may interfere with the breakdown of caffeine, exposing the body to the effects of caffeine for longer periods of time. Medications that act as stimulants may enhance the effects of caffeine and lead to severe side effects.

Decaffeinated tea is the result of additional processing. This usually involves a chemical process to remove the caffeine naturally contained in the tea leaves. The exact method used may have an effect on the resulting flavor and level of antioxidants in the decaffeinated tea. Consumers may be able to reduce caffeine levels in their tea at home. Because most of the caffeine in tea is released within the first 30 seconds that tea is infused with hot water, discarding the first infusion (after 20 to 30 seconds) and then replacing the hot water may help.  

Herbal teas are made from herbs or plants other than the tea plant and as a result, certain herbal teas may have different effects on the body. For example, senna is believed to have a laxative effect, chamomile a sedative effect, and peppermint is associated with helping to relieve an upset stomach. Many herbal teas are marketed as aids for losing weight, quitting smoking or relieving premenstrual symptoms. However, no conclusive scientific evidence exists that supports these claims.

Herbal teas may be harmful in certain circumstances. For example, herbs that have a laxative effect may be dangerous for people on severely restricted diets. People with allergies may not realize a certain herb is associated with a particular allergen. For example, chamomile is related to ragweed, asters and chrysanthemums. People allergic to any of those plants may experience an allergic reaction to chamomile tea.

In addition, certain herbs sold as teas are associated with severe side effects, especially when taken in large amounts. These include:

• Comfrey (liver disease)
  
  
• Lobelia (breathing problems, vomiting, seizures, coma, death)
  
  
• Ephedra (abnormal heart rate, death)

Tea is considered a type of functional food. It contains phytochemicals (primarily catechins) associated with certain health benefits, such as a lowered risk of some cancers and cardiovascular disease. Catechins are predominantly found in tea, but may also be present in other foods such as apples, red wine and chocolate.

Herbal teas are made from plants other than the tea plant. While they do not actually contain tea, they may contain antioxidants or other components associated with health benefits. Thus, they may also provide certain health benefits, although there is insufficient scientific evidence regarding the safety or effectiveness of most herbs.

Tea components or extracts may also be available in supplement form. As is the case with herbs, there is a lack of well-designed scientific studies concerning the safety and effectiveness of tea supplements. In addition, adverse side effects have occurred with tea supplements, including nausea, vomiting, diarrhea, insomnia, fatigue, abdominal pain and confusion.

The U.S. Food and Drug Administration (FDA) has not authorized any health claims or qualified health claims that associate tea with a reduced risk of any type of disease or medical condition. This includes tea consumed as a beverage or tea components contained in supplement form. Thus, no claims of these sorts may be mentioned on labels of tea products or supplements. Products that claim to cure, prevent or treat a specific disease are considered drugs and are required to be regulated as such by the FDA.

The FDA specifically rejected manufacturers’ petitions that linked green tea with a reduced risk of breast cancer, prostate cancer or cardiovascular disease. The FDA found insufficient scientific evidence to warrant approval of any of these claims.

However, certain other types of claims may be allowed on labels of tea products or supplements. These include:

• Structure-function claims. These describe the effect of a particular bioactive food component on body structure or function, but cannot imply it cures or treats a disease. For example, the statement “Flavonoid antioxidants help protect the body against free radicals, molecules that can damage cells” refers to the component’s effect on the body without implying association with a specific disease or medical condition. These claims must not be false or misleading, and must be accompanied by a disclaimer stating that the FDA has not evaluated the claim and that the product is not intended to diagnose, treat, cure or prevent any disease.
  
  
• Nutrient content claims. These involve quick comparative references to nutrient levels in a product (e.g., low fat). However, these claims cannot be made about components for which there are no national dietary recommendations (e.g., antioxidants). This is because it would be impossible to determine what level of the component may be considered high or low.    

In addition, herbal teas are required by the FDA to include the name of the plant the product comes from (e.g., chamomile) on the product label. Herbal teas may be considered either a food or supplement, depending on the intended use. When consumed for their taste and aroma, they are considered a food. When consumed for medicinal value, they may be considered a supplement (in which case, the label is required to include “supplement” as a product identifier). Women should talk to their physicians about drinking herbal tea during pregnancy.

Product advertising is regulated by the Federal Trade Commission (FTC), not the FDA. The FTC currently uses more lenient standards than the FDA on product health claims. Thus, advertising for tea products may contain health claims that are not permitted by the FDA  on product labels.  

Many marketers of herbal teas avoid making health claims by including language such as “relaxing” or “soothing” on their labels. 

Preparing questions in advance can help patients have more meaningful discussions with health professionals regarding their conditions. Patients may wish to ask their doctor or registered dietitian the following questions related to tea:

1. Is tea good for me? Why or why not?
   
   
2. How much tea is it safe for me to consume every day?
   
   
3. Of the four major types of tea, what type do you recommend for me? Why?
   
   
4. Do you recommend herbal teas? If so, what type? How can it benefit me?
   
   
5. How safe and effective are herbal teas?
   
   
6. Will the tea I drink interact with any medications (prescription and over-the-counter) I currently take?
   
   
7. Are there certain over-the-counter medications or supplements I should avoid if I consume tea?
   
   
8. Do you recommend I take supplements instead of drinking tea?
   
   
9. What are the possible side effects of these supplements?
   
   
10. What type of symptoms associated with my tea use should I report to you?