Theanine is an amino acid, which is a building block of protein. It is a prominent component of Camellia sinensis, an evergreen shrub used to make green, black, white, and oolong tea. It is also known commercially as Suntheanine, and in scientific circles as [gamma]-glutamylethylamide and [gamma]-ethylamino-L-glutamic acid. Theanine is also found in other Camellia species and in a type of mushroom.
Theanine is a substance in tea that is made by steeping leaves from an evergreen shrub known as a tea plant or tea tree. The scientific name for the tea plant is Camellia sinensis, and it is in the family Theaceae. At one time, the plant had the genus name Thea instead of Camellia, and this led to the amino acid’s name of theanine. The tea plant can reach 20–30 feet in height. It has fragrant, yellow-centered, white flowers and oblong, dark green leaves that can grow to as much as a foot long. Leaves from Camellia sinensis are used to make green, black, white, and oolong tea.
The twigs and stems of the plant are also used to make another type of tea known as kukicha.
Camellia sinensis, a native plant in South Asia and Southeast Asia, is now grown in many tropical and subtropical regions of the world, where its leaves are gathered, dried, and eventually used to make tea. Tea plants arrived in North America in the late 1700s courtesy of Andre´ Michaux, a French botanist who tried to begin a crop near Charleston, South Carolina, but Michaux returned to Europe before the crop had taken hold. Two other major attempts to grow tea in the United States began in 1848 and in 1874, but both were halted following the untimely deaths of the teaplantation owners. Finally in 1888, Charles Shepard and his plantation in Summerville, South Carolina, began producing tea. The oolong tea produced by his farm, called the Pinehurst Tea Plantation, was good enough to win first prize at the 1904 World’s Fair. Tea is still grown in the United States, particularly in the humid Southeast.
Tea made from the leaves of Camellia sinensis has been a popular beverage for many years, first in South and Southeast Asia, and later in Europe, the United States, and other parts of the world. Most people drink it because they enjoy it, but tea is also a healthful beverage. Consumption of tea has been linked to such benefits as cancer prevention, decreased risk of stroke, a strengthened immune system, and reduced blood cholesterol. Historically, green tea in particular has been used as a relaxing agent.
Camellia sinensis is one of the few known plants to contain the amino acid theanine. It is also found in other Camellia species (C. japonica and C. sasanqua) and in a mushroom known as bay bolete (Xerocomus badius or Boletus badius). Theanine was first isolated from green tea in 1949. Theanine comes in two forms that are identical in chemical structure and composition, but are mirror images of one another. The vast majority of theanine in tea leaves is the form called L-theanine.
Many scientific studies of the purported benefits of tea made with the leaves of Camellia sinensis have focused on L-theanine.
Scientific studies have shown that L-theanine helps relieve anxiety and stress, including among those with schizophrenia; and heightens the activity of nerve cells in the brain and improves concentration. When combined with caffeine, it helps people to focus on the tasks at hand better than those who consume theanine or caffeine alone, or those who had consumed neither. Other research has noted that theanine does not cause jitteriness associated with caffeine, and that it lessens the increases in blood pressure that caffeine promotes. Some researchers even suggest that tea may reduce the risk of cardiovascular and cerebrovascular disease, although that reduction may be related to other compounds in tea, such as antioxidants called catechins. The tea plant converts theanine into catechins.
Research has evaluated the effect of L-theanine (Suntheanine) on attention and reaction time response. For one study, which was published in the Journal of Functional Foods, researchers used an anxiety scale (specifically, the manifest anxiety scale) to divide 18 university students into two groups: one that was prone to high anxiety, and the other that was not. Within those groups, some of the students received water (a placebo) and others received water combined with water-soluble theanine powder. While the consumption of theanine in water had no effect on the low-anxiety group compared to placebo, it did have a noticeable impact on the high-anxiety group. Those students experienced several changes: a significantly enhanced activity of brain waves that are associated with relaxation and alertness; a descending heart rate; an increase in performance on a visual test (participants watched numbers flash on a monitor and were instructed to press a button when certain numbers appeared); and improved reaction-time response.
Theanine also has positive effects on individuals with schizophrenia and attention deficit hyperactivity disorder (ADHD), according to research. For the latter, a study measured sleep quality among boys who had been formally diagnosed with ADHD, and found that 400 mg daily of L-theanine was a safe treatment that promoted better sleep.
Theanine may also improve the effectiveness of various agents used to treat cancer. Animal studies have shown that it enhances the antitumor activity of the cancer-treatment agent known as doxorubicin and of other chemotherapy agents, and had anti-cancer properties for a number of different cancers, including leukemia, colon, breast, liver, prostate, and lung cancers. An example of the research in this area is a study published in the journal Cytotechnology. Scientists investigated the effects of theanine on human lung cancer and leukemia cells, and found that it suppressed the growth of both types of cancer cells, and the ability of the lung cancer cells to migrate and invade other cells. In addition, theanine enhanced the anticancer activity of several anticancer agents. They concluded, ‘‘Our present results suggest that theanine may have the wide therapeutic and/or adjuvant therapeutic application in the treatment of human lung cancer and leukemia.’’
The Journal of Cancer Research and Clinical Oncology published an article that reviewed the research on tea’s overall benefits, and suggested that consuming 10 Japanese-size cups of green tea a day helped to prevent several types of cancer and protected against the recurrence of colorectal cancer.
Practitioners of herbal medicine may prescribe theanine supplements to boost the immune system, counter anxiety, promote a good night’s sleep, improve mood, and heighten both learning and memory. Many anti-anxiety medications make users drowsy, but theanine does not appear to have this side effect. Some users take theanine supplements to help them focus on tasks and to promote creativity. Theanine is also sometimes prescribed to treat high cholesterol. In addition, it may be beneficial in protecting individuals against cerebral ischemia, which is insufficient blood flow to the brain often caused by a stroke.
Tea from these leaves can be processed into black, green, oolong, or white tea. The upper leaves of the plant are used to make black, green, and oolong tea; the leaf buds and some new leaves are used to make white tea. Black tea is made by wilting the leaves and then rolling them while exposing them to oxygen, a process known as oxidation, which makes the leaves dark brown or black.
Oolong leaves are only partially oxidized. Green and white leaves are steamed or fired (exposed to heat), which inactivates the enzymes that promote oxidation, so green and white tea leaves are unoxidized.
To make tea, experts recommend that black and oolong tea leaves be steeped in water at approximately the boiling point (212 degrees Fahrenheit) and that green and white tea leaves be steeped in water that has boiled but then cooled to about 165–185 degrees Fahrenheit. Properly heated water will produce a green-colored cup of green tea, while overly heated water will produce more of a yellow-colored cup of green tea as well as a bitter flavor.
Theanine is available as a supplement that comes in capsule form. Researchers often use powdered theanine, which dissolves in water and has no taste. This helps in studies that compare the effects of theanine to placebo (water without theanine). Herbal practitioners may prescribe doses of 100–400 mg of theanine per day.
Individuals should consult their primary healthcare physician about any health problems they have and refrain from self-treating such conditions as high blood pressure or high cholesterol with tea or other alternative-medicine choices. In addition, women who are pregnant or lactating should consult a primary healthcare physician about the use of any supplements.
No known side effects exist. Theanine promotes relaxation without the sedative side effects common to other anti-anxiety supplements.
Persons who are taking medications to lower blood pressure or lipids, or who are undergoing chemotherapy should consult their primary healthcare physician before taking theanine supplements, which may boost the effects of those agents. In addition, theanine may counter the stimulating action of caffeine or other similar agents.