Green, black, and oolong teas all come from the same plant, Camellia sinensis, but are prepared using different methods. To produce green tea, fresh leaves from the plant are lightly steamed.
Tea has been used for medicinal purposes in China and Japan for thousands of years.
Current uses of green tea as a beverage or dietary supplement include improving mental alertness, relieving digestive symptoms and headaches, and promoting weight loss. Green tea and its extracts, such as one of its components, EGCG, have been studied for their possible protective effects against heart disease and cancer.
Green tea is consumed as a beverage. It is also sold in liquid extracts, capsules, and tablets and is sometimes used in topical products (intended to be applied to the skin).
Green Tea in Health Research
Although many studies have been done on green tea and its extracts, definite conclusions cannot yet be reached on whether green tea is helpful for most of the purposes for which it is used.
Green Tea Health Summary
There’s evidence that green tea enhances mental alertness, as would be expected because of its caffeine content.
The U.S. Food and Drug Administration has approved a specific green tea extract ointment as a prescription drug for treating genital warts.
Studies of green tea and cancer in people have had inconsistent results. The National Cancer Institute does not recommend for or against using green tea to reduce the risk of any type of cancer.
Very few long-term studies have investigated the effects of tea on heart disease risk. However, the limited evidence currently available suggests that both green and black tea might have beneficial effects on some heart disease risk factors, including blood pressure and cholesterol.
Green tea extracts haven’t been shown to produce a meaningful weight loss in overweight or obese adults. They also haven’t been shown to help people maintain a weight loss.
The National Center for Complementary and Integrative Health (NCCIH) is funding research on green tea and its extracts, including studies of the effects of high doses of tea components on the liver, whether substances in green tea can be helpful for iron overload disease, and the safety of a component of green tea in people who are HIV-positive.
Green Tea Safety
Green tea, when consumed as a beverage, is believed to be safe when used in moderate amounts.
Liver problems have been reported in a small number of people who took concentrated green tea extracts. Although the evidence that the green tea products caused the liver problems is not conclusive, experts suggest that concentrated green tea extracts be taken with food and that people discontinue use and consult a health care provider if they have a liver disorder or develop symptoms of liver trouble, such as abdominal pain, dark urine, or jaundice.
Except for decaffeinated green tea products, green tea and green tea extracts contain substantial amounts of caffeine. Too much caffeine can make people feel jittery and shaky; interfere with sleep; and cause headaches.
Green tea has been shown to reduce blood levels (and therefore the effectiveness) of the drug nadolol, a beta-blocker used for high blood pressure and heart problems. It may also interact with other medicines.
Jurgens TM, Whelan AM, Lillian L, et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database of Systematic Reviews. 2012;(12):CD008650. Accessed at https://www.thecochranelibrary.com(link is external) on April 16, 2015.
Source: National Center for Biotechnology Information (NCBI)[Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information;  – [cited 2018 Apr 5]. Available from: https://www.ncbi.nlm.nih.gov/
Search query:(Camellia sinensis AND diabetes AND (( Clinical Trial[ptyp] OR systematic[sb] ) AND Humans[Mesh]))
Tea made from leaves is one of the most consumed beverages worldwide. This systematic review aims to update pharmacological activity on metabolic and endocrine disorders. Inclusion criteria were preclinical and clinical studies of tea extracts and isolated compounds on osteoporosis, hypertension, diabetes, metabolic syndrome, hypercholesterolemia, and obesity written in English between 2014 and 2019 and published in Pubmed, Science Direct, and Scopus. From a total of 1384 studies, 80 reports met inclusion criteria. Most papers were published in 2015 (29.3%) and 2017 (20.6%), conducted in China (28.75%), US (12.5%), and South Korea (10%) and carried out with extracts (67.5%, especially green tea) and isolated compounds (41.25%, especially epigallocatechin gallate). Most pharmacological studies were and studies focused on diabetes and obesity. Clinical trials, although they have demonstrated promising results, are very limited. Future research should be aimed at providing more clinical evidence on less studied pathologies such as osteoporosis, hypertension, and metabolic syndrome. Given the close relationship among all endocrine disorders, it would be of interest to find a standard dose of tea or their bioactive constituents that would be beneficial for all of them.
Diabetes mellitus and dyslipidemia are currently increasing dramatically, and conventional medicine in the treatment of them has limited efficacies and serious adverse effects. (L.) Less. tea (PIT) is widely consumed as a health-promoting drink in Southeast Asia. This study aimed to investigate whether tea has antidyslipidemic and antihyperglycemic effects and toxicity in humans. A randomized clinical trial. Nakhonratchasima, Thailand. Forty-five participants with prediabetes. Participants were randomized to receive placebo tea, 1.5 g of PIT, and 1.5 g tea (green tea, CST) once daily for 12 weeks. The oral glucose tolerance test (OGTT), total cholesterol, triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), blood urea nitrogen (BUN), creatinine, alanine transaminase (ALT), alkaline phosphatase (ALP), and complete blood count (CBC) before and after treatment were investigated. The results showed that PIT significantly ameliorated hyperglycemia and significantly lower serum TG (109.22 ± 5.21 mg/dL) and LDL-C (122.20 ± 3.67 mg/dL) than placebo (145.56 ± 8.18 and 142.07 ± 8.58 mg/dL, respectively) ( < 0.05). Moreover, PIT exhibited serum TG (109.22 ± 5.21 mg/dL) significantly lower than CST (124.38 ± 4.70 mg/dL) ( < 0.05). In addition, the serum HDL-C of PIT (57.56 ± 3.05 mg/dL) was significantly higher than the placebo (46.44 ± 2.47 mg/dL) ( < 0.05). Furthermore, the toxicity testing showed that no significant difference in BUN, creatinine, ALT, ALP, and CBC of PIT-treated group compared with the placebo ( > 0.05). These results suggest that PIT may ameliorate hyperglycemia and dyslipidemia in prediabetes people. It may not be toxic to the kidney, liver, and blood. So, PIT has the potential to develop to be a health-promoting tea or herbal medicine for hyperglycemia and dyslipidemia prevention.
Leaf teas are widely used as a purported treatment for dysregulated glucose homeostasis. The objective of this study was to systematically evaluate the clinical and cellular-metabolic evidence, published between January 2013 and May 2019, and indexed on PubMed, ScienceDirect, and Web of Science, supporting the use of leaf teas for this purpose. Fourteen randomized controlled trials (RCTs) (13 on teas) were included, with mixed results, and providing scant mechanistic information. In contrast, 74 animal and cell culture studies focusing on the pancreas, liver, muscle, and adipose tissue yielded mostly positive results and highlighted enhanced insulin signaling as a recurring target associated with the effects of teas on glucose metabolism. We conclude that more studies, including RCTs and pre-clinical studies examining teas from a wider variety of species beyond , are required to establish a stronger evidence base on the use of leaf teas to normalize glucose metabolism.