It's common to hear tea, especially green tea, touted as a panacea for all of life's ailments. In this article we will cut through the chatter and get to know the health benefits of tea and the compounds responsible for them. All types of tea have exceptional health benefits. By "tea" we are referring to the liquor that results from brewing the leaves of the Camellia Sinensis (tea) plant, wether it's white, green, oolong, or black tea. All tea types have similar health benefits, with a few minor differences.
Tea leaves contain a few key compounds: polyphenols, amino acids, methylxanthines, carotenoids, enzymes, pigments, carbohydrates, minerals and a variety of volatile flavor and aromatic compounds. Not only are these responsible for tea's appearance, aroma, and flavor, they also have powerful health effects on the body. In this article we will focus on the first three.
Polyphenols are a type of antioxidant and plant metabolite produced as a protection against parasites, oxidative injury, and harsh weather conditions and are the most abundant compounds in tea accounting for as much as 30-40% of the solids in tea liquor. Polyphenols are derived from amino acids via sunlight, so shade grown tea contains less of them. The bud and first leaf of the plant have the most polyphenols. Responsible for astringency, there are an estimated 30,000 polyphenols in tea leaves but the most important ones are types of flavanols called catechins.
Tea catechins include catechin (C), epicatechin (EC), epicatechin gallate (ECG), gallocatechin (GC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). EGCG is the most abundant and active and is the primary compound responsible for the health benefits of green tea and white tea. In addition, tea also contains the flavonoid compounds flavonols, flavones, isoflavones, and anthocyanins. During tea oxidation, a chemical reaction takes place that converts catechins to other polyphenols called catechol tannins, specifically theaflavins and thearubigins that are abundant in oxidized teas like black tea and oolong tea.
Catechins are powerful antioxidants and reduce oxidative stress on the body by neutralizing free radicals. EGCG in particular has been shown in numerous studies to help prevent and even reverse cancer growth. Green tea and white tea are highest in these catechins and thus have the highest anti-cancer effects. These catechins also have been found to decrease LDL cholesterol while increasing HDL cholesterol, as well as lower blood glucose and improve insulin sensitivity. Catechins have powerful anti-inflammatory effects in the body. Chronic inflammation is connected to almost every modern ailment and disease, including arthritis, metabolic syndrome, cancer, and depression.
Making up 6% of the solids in tea liquor, amino acids give tea an umami flavor. Tea grown in the shade has more amino acids because sunlight doesn't have a chance to convert amino acids to polyphenols. There are many amino acids found in tea but the most abundant is L-Theanine, or theanine. Tea is one of only three knows sources of theanine, the others being the mushroom boletus badius, and the plant guayusa. Since it is able to cross the blood-brain barrier, theanine has psychoactive properties. It can promote alpha brain wave activity, reduce stress, improve cognition, and aid relaxation. Theanine has a synergistic effect with the caffeine in tea and tends to create an enhanced state of mental clarity sometimes referred to as "mindful alertness."
Methylxanthines in tea include the stimulant caffeine, theobromine, and theophylline. Methylxanthines make up 2-5% of the dry weight of fresh tea leaves and contribute to a bitter taste in the tea liquor. Contrary to popular belief, caffeine levels do not correspond to general tea types. Black tea does not contain more caffeine than green or white tea. Caffeine does occur in varying amounts in individual teas, and in different plant cultivars, stages of growth, and parts of the plant. Brewing method also influences the amount of caffeine in the tea. Caffeine in conjunction with catechins can increase metabolism by helping facilitate the conversion of body fat into energy. This can help improve exercise performance and aid weight loss. In tea the effects of caffeine are complemented by theophylline. While caffeine is primarily active in the brain and muscles, theophylline has general anti-inflammatory properties and relaxes smooth muscles in the airway, making breathing easier while also stimulating both the rate and force of heart contractions. Theobromine can also stimulate the heart and improves blood flow around the body, leading to a net reduction in blood pressure. It also has a mild diuretic effect.
Tea leaves can contain around 30 vitamins and minerals including thiamine (vitamin B1), riboflavin (vitamin B2), ascorbic acid (vitamin C), vitamin E, folic acid, manganese, magnesium, nickel, selenium, iodine, and potassium. Tea also contains the carotenoid antioxidants beta-carotene, lutein and zeaxanthin, as well as chlorophyll and enzymes. The exact mineral composition in tea leaves is heavily dependent on terroir, or the geographic region, elevation, soil quality, weather, and microclimate that the tea is grown in.
The combined effects of the active ingredients in tea, primarily catechins, theanine, and methylxanthines, have been shown to:
help prevent cancer, and even reverse it
reduce chronic inflammation and the risk of diseases associated with it
improve mental clarity, focus, memory, and reduce cortisol and stress levels
improve exercise performance and aid weight loss
improve cholesterol levels and heart health
prevent tooth decay and bad breath
reduce oxidative stress and reduce effects of aging