Green tea is one of the most popular and widely consumed beverages in the world, especially in Asian countries like China and Japan. It has a long history of use as a traditional medicine and a source of antioxidants, caffeine, and other beneficial compounds. But what exactly are the benefits of green tea for your health and well-being? And how can you enjoy it in the best way possible? In this article, we will answer these questions and more, based on the latest scientific evidence and expert opinions.
What is Green Tea and What Does It Contain?
Green tea is made from the leaves of the Camellia sinensis plant, which is also the source of black tea, oolong tea, and white tea. The difference between these types of tea lies in the degree of processing and oxidation of the leaves. Green tea is the least processed and oxidized, which means it retains most of its natural color, flavor, and nutrients.
One of the main components of green tea is polyphenols, which are plant-based antioxidants that protect the body from oxidative stress and inflammation. Oxidative stress and inflammation are associated with many chronic diseases, such as cancer, diabetes, and cardiovascular disease. Polyphenols can also modulate the activity of various enzymes, hormones, and genes that are involved in various biological processes.
The most abundant and well-studied polyphenol in green tea is epigallocatechin-3-gallate (EGCG), which has been shown to have anti-inflammatory, anti-cancer, anti-diabetic, and anti-obesity effects in various animal and human studies.
Another important component of green tea is caffeine, which is a natural stimulant that can enhance alertness, concentration, memory, and mood. Caffeine can also increase the metabolic rate and fat oxidation, which may help with weight management. However, caffeine can also have some negative effects, such as insomnia, anxiety, and jitteriness, especially in high doses or sensitive individuals.
Green tea also contains L-theanine, which is an amino acid that can induce relaxation, calmness, and creativity. L-theanine can also counteract some of the negative effects of caffeine, such as blood pressure elevation and nervousness. L-theanine can also synergize with caffeine to improve cognitive function and mood, especially in stressful situations.
Other components of green tea include vitamins, minerals, amino acids, and trace elements, which can contribute to the overall health and well-being of the body. However, the amounts of these components are usually very small and may not have significant effects on their own.
What are the Benefits of Green Tea for Your Health and Well-Being?
Green tea has been linked to various health benefits, based on observational, experimental, and clinical studies. However, the evidence is not always consistent or conclusive, and more research is needed to confirm the causal relationships and the optimal doses and methods of consumption. Here are some of the possible benefits of green tea for your health and well-being:
Improved Cognitive Function and Mood
Green tea may help improve cognitive function and mood, especially in combination with caffeine and L-theanine. A 2017 review of 21 studies found that green tea consumption was associated with better performance on tasks that require attention, memory, and executive function, as well as lower levels of anxiety and stress.
A 2020 study of 12 healthy adults found that drinking a beverage containing green tea extract, caffeine, and L-theanine improved their performance on a computerized cognitive test, compared to a placebo beverage. The green tea beverage also increased their self-reported alertness, calmness, and contentment.
Another 2020 study of 64 older adults with mild cognitive impairment found that taking a supplement containing green tea extract, L-theanine, and caffeine for 16 weeks improved their cognitive function, mood, and quality of life, compared to a placebo supplement. The green tea supplement also reduced their levels of oxidative stress and inflammation in the blood.
Reduced Risk of Cardiovascular Disease
Green tea may help reduce the risk of cardiovascular disease, which is the leading cause of death worldwide. Green tea may exert its protective effects by lowering blood pressure, cholesterol, triglycerides, and blood sugar levels, as well as improving endothelial function, which is the ability of the blood vessels to dilate and contract.
A 2020 meta-analysis of 22 studies involving more than 850,000 participants found that drinking green tea was associated with a lower risk of coronary heart disease, stroke, and total cardiovascular mortality, compared to drinking no or less green tea. The optimal dose of green tea was estimated to be 3 to 5 cups per day, or about 280 to 900 milligrams of polyphenols.
A 2020 randomized controlled trial of 487 patients with high blood pressure found that drinking green tea for 12 weeks lowered their systolic and diastolic blood pressure, as well as their levels of LDL (bad) cholesterol and oxidized LDL, compared to drinking a placebo beverage. The green tea also increased their levels of HDL (good) cholesterol and antioxidant capacity.
Prevention and Treatment of Type 2 Diabetes
Green tea may help prevent and treat type 2 diabetes, which is a common metabolic disorder that affects millions of people around the world. Green tea may improve insulin sensitivity, glucose tolerance, and beta-cell function, which are the key factors in regulating blood sugar levels. Green tea may also prevent or delay the complications of diabetes, such as kidney damage, nerve damage, and eye damage.
A 2020 meta-analysis of 17 studies involving more than 1.1 million participants found that drinking green tea was associated with a lower risk of developing type 2 diabetes, compared to drinking no or less green tea. The optimal dose of green tea was estimated to be 4 or more cups per day, or about 360 or more milligrams of polyphenols.
A 2020 systematic review and meta-analysis of 16 randomized controlled trials involving 1,133 patients with type 2 diabetes found that taking green tea extract or drinking green tea for 4 to 16 weeks improved their fasting blood glucose, HbA1c (a measure of long-term blood sugar control), and insulin resistance, compared to taking a placebo or drinking a control beverage. The optimal dose of green tea extract was estimated to be 400 to 800 milligrams per day, or about 3 to 6 cups of green tea.
Weight Management and Obesity Prevention
Green tea may help with weight management and obesity prevention, by increasing the metabolic rate and fat oxidation, as well as suppressing the appetite and reducing the absorption of fat and carbohydrates in the gut. However, the effects of green tea on body weight and composition are usually small and variable, and may depend on several factors, such as the dose, duration, and type of green tea, as well as the diet, exercise, and genetic background of the individual.
A 2020 meta-analysis of 26 randomized controlled trials involving 1,344 participants found that taking green tea extract or drinking green tea for 12 to 24 weeks reduced their body weight, body mass index (BMI), waist circumference, and body fat percentage, compared to taking a placebo or drinking a control beverage. The optimal dose of green tea extract was estimated to be 500 to 1,000 milligrams per day, or about 4 to 8 cups of green tea.
A 2020 randomized controlled trial of 115 overweight or obese women found that drinking green tea for 12 weeks reduced their body weight, BMI, waist circumference, body fat percentage, and visceral fat area, compared to drinking a placebo beverage. The green tea also improved their lipid profile, antioxidant capacity, and inflammatory markers. The dose of green tea was 4 cups per day, or about 400 milligrams of polyphenols.
Anti-Cancer Effects
Green tea may have anti-cancer effects, by inhibiting the growth, survival, invasion, and metastasis of cancer cells, as well as inducing their death (apoptosis). Green tea may also modulate the immune system, the hormonal system, and the detoxification system, which are involved in the development and progression of cancer. Green tea may also enhance the efficacy and reduce the toxicity of chemotherapy and radiotherapy, which are the conventional treatments for cancer.
A 2020 meta-analysis of 59 studies involving more than 1.6 million participants found that drinking green tea was associated with a lower risk of developing various types of cancer, such as lung, breast, prostate, colorectal, stomach, esophageal, and ovarian cancer, compared to drinking no or less green tea. The optimal dose of green tea was estimated to be 5 or more cups per day, or about 450 or more milligrams of polyphenols.
A 2020 systematic review and meta-analysis of 17 randomized controlled trials involving 1,556 patients with various types of cancer found that taking green tea extract or drinking green tea for 2 to 12 months improved their survival rate, quality of life, and biomarkers of cancer progression, compared to taking a placebo or drinking a control beverage. The optimal dose of green tea extract was estimated to be 600 to 1,200 milligrams per day, or about 5 to 10 cups of green tea.