Green tea contains many antioxidants that promote weight loss, provide protection against cancer, and lower the risk of heart disease.
Green tea is brewed from the leaves of the Camellia sinensis plant, and is the most consumed beverage worldwide other than water. Traditionally, green tea has been used in Indian and Chinese medicine. Increasing interest in the health benefits of tea has led to the addition of tea extracts in dietary supplement form.
Since green tea is unprocessed, it is rich in protective polyphenols. The main polyphenols in green tea are flavonoids, including catechins and epigallocatechin gallate (EGCG). Green tea leaves usually contain 10-20% catechins. These powerful antioxidants have numerous health benefits, including improved brain function, fat loss, protection against cancer and other diseases, prevention of cell damage, and lowered risk of heart disease. Antioxidants can also be found in fruits, vegetables, and unprocessed foods.
Green tea also contains other nutrients including magnesium, folate, B-vitamins, and amino acids. As part of a healthy and balanced diet, green tea can be a good source of antioxidants and essential nutrients.
Here we review three of the top health benefits of green tea:
Green tea promotes weight loss
Drinking green tea has previously been associated with weight loss. One reason for this may be that the epigallocatechin gallate present in green tea boosts metabolism and fat-burning, particularly in the abdominal area. Abdominal fat is dangerous as it is associated with many different chronic diseases.
A study published in Physiology & Behavior with sixty obese participants found that green tea extract helped the individuals to reduce their weight by an additional 7.3 pounds and burn 183 more calories than those who did not drink green tea over twelve weeks. Another study published in Obesity involving 240 participants with obesity found a significant decrease in body weight, body fat percentage, waist circumference, abdominal fat, and cholesterol levels in the green tea group compared to those who did not consume green tea over twelve weeks.
An important note is that the benefits of green tea on weight loss are aided by regular exercise. A study published in Journal of Health Science involving fourteen healthy males found that there was a significant increase in fat loss for energy expenditure in individuals who combined exercise and tea catechins intake in comparison to those who exercised but did not consume any green tea.
Green tea is particularly effective when consumed as an alternative to sodas and less healthy options.
Green tea may provide protection against cancer
Cancer can be caused by uncontrollable cell growth and oxidative damage. According to the National Cancer Institute, the protective polyphenols in tea appear to have a link to reduced tumour growth. The antioxidants in green tea can help protect against oxidative damage.
Some studies have indicated that consumption of green tea leads to a reduced risk of different types of cancers. Green tea appears to have anti-carcinogenic properties. A study published in Breast Cancer Research and Treatment found that increased consumption of green tea was associated with a reduced risk of breast cancer by 20-30%. A Japanese study published in the American Journal of Epidemiology found a decreased risk of advanced prostate cancer in men who drank more cups of green tea daily.
In a study published in Cancer Epidemiology and Prevention Biomarkers, it was found that a daily intake of ten small cups of green tea supplemented with tablets of green tea extract limited the recurrence of colorectal polyps.
However, the mechanism by which the antioxidants in green tea interact with cancer cells is unknown. It is assumed that the mechanism suppresses cell growth, increases apoptosis (programmed cell death), and inhibits angiogenesis (formation of new blood vessels).
Green tea reduces risk of heart disease and other medical conditions
Cardiovascular diseases are the leading causes of death globally. An investigation published in the Journal of the American Medical Association concluded that there was a significantly lower risk of mortality, especially due to cardiovascular diseases, in individuals who drank at least five cups of green tea per day compared to one cup.
Health benefits of green tea include improved blood flow, lowered cholesterol, reduced inflammation, and improved heart functioning. Green tea extract has anti-inflammatory properties due to the presence of flavonoids. Inflammation is connected to conditions such as arthritis, irritable bowel syndrome (IBS), and period pains.
Catechins in green tea may reduce the risk of type 2 diabetes by decreasing blood sugar levels and improving insulin sensitivity. A study published in Annals of Internal Medicine with a five-year follow-up found a 42% reduced risk of type 2 diabetes in men and women who drank green tea daily.
It is important to remember that green tea does contain caffeine; for this reason, daily consumption of green tea should be limited in individuals who are sensitive to caffeine. However, moderate levels of caffeine improve brain function including mood, reaction time, and memory. In addition to caffeine, green tea contains the brain-boosting compound amino acid L-theanine. L-theanine may cause improved brain function and anti-anxiety effects by increasing the levels of certain neurotransmitters (chemical messengers) in the blood.
The various health claims surrounding green tea is inconclusive, so future research is essential to provide more evidence. However, it is clear that green tea has a range of potential health benefits.
Written by Albina Babu, MSc
Is green tea good for you? (2018). BBC Good Food. Retrieved from: https://www.bbcgoodfood.com/howto/guide/health-benefits-green-tea
Auvichayapat, P., et al. (2008). Effectiveness of green tea on weight reduction in obese Thais: a randomized, controlled trial. Physiology & Behavior, 93(3), pp.486-491.
Nagao, T., Hase, T. and Tokimitsu, I. (2007). A green tea extract high in catechins reduces body fat and cardiovascular risks in humans. Obesity, 15(6), pp.1473-1483.
Ota, N., et al. (2005). Effects of combination of regular exercise and tea catechins intake on energy expenditure in humans. Journal of Health Science, 51(2), pp.233-236.
Ogunleye, A.A., Xue, F. and Michels, K.B. (2010). Green tea consumption and breast cancer risk or recurrence: a meta-analysis. Breast Cancer Research and Treatment, 119(2), p.477.
Kurahashi, N., et al. (2008). Green tea consumption and prostate cancer risk in Japanese men: a prospective study. American Journal of Epidemiology, 167(1), pp.71-77.
Yang, C.S. and Wang, H. (2016). Cancer preventive activities of tea catechins. Molecules, 21(12), p.1679.
Iso, H., et al. (2006). The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults. Annals of Internal Medicine, 144(8), pp.554-562.
Shimizu, M., et al. (2008). Green tea extracts for the prevention of metachronous colorectal adenomas: a pilot study. Cancer Epidemiology and Prevention Biomarkers, 17(11), pp.3020-3025.
Suganuma, M., Saha, A. and Fujiki, H. (2011). New cancer treatment strategy using combination of green tea catechins and anticancer drugs. Cancer Science, 102(2), pp.317-323.
Kuriyama, S., et al. (2006). Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA, 296(10), pp.1255-1265.
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