Tea Time! Health Benefits of Green Tea
- Jul 22, 2016
- 4 min read
Image: Prostate Supplements
Tea has been increasing in popularity over the past decade. More and more establishments are selling teas and tea products. Health food stores have entire tea sections. And little tea shops are popping up all over the place. Tea is the is the most widely-consumed beverage after water. According to the Tea Association of the USA, 80% of US households have tea. Black tea accounts for 85% of the tea drank in the United States. Green tea, the focus of this post, makes up just 14% of the tea consumed by Americans.
Tea originates from the Camellia sinesis plant. There are 5 main varieties of tea: green, black, white, oolong, and pu-erh. The type of tea is determined by the amount of time the leaves are exposed to air (or oxidized). White tea is unoxidized and made from tiny, unopened plant buds. Green tea is produced from the green leaves before any oxidation has happened. Oolong is made from partially oxidized tea leaves. Black tea, as the name suggests, is made from totally oxidized leaves. Pu-erh is also fully oxidized and is fermented by bacteria, giving it a earthy flavor. Herbal infusions like chamomile, ginger, and licorice "teas" are not really tea at all, so they do not deliver the same health benefits.
Health Benefits of Green Tea
The health benefits of green tea, arise from the antioxidants found in it, called flavonoids or catechins. (For more information on flavonoids, see HERE) Green tea is often stated to have the most benefits, but all teas contain antioxidants. However, as tea leaves are oxidized, the levels of their catechins decrease.
When looking at research and data surrounding tea, it's important to realize that many of these studies are merely observation, which has a difficult time accurately associating something with an outcome. Also, green tea is primarily drank in Asia and the Asian lifestyle and diet are very different from the United States. Brewing method may also influence the amount of antioxidants in tea.
Heart Disease
The most promising health benefits of tea are related to heart disease. The flavonoids in green tea help prevent oxidation of LDL ("bad") cholesterol which, in turn, helps prevent it from forming plaque in arteries. It has also been shown to lower total cholesterol and raise HDL ("good") cholesterol.
Weight Loss
Perhaps one of the main reasons for tea's rise in popularity is its supposed ability to promote weight loss. The weight loss market is saturated with products boasting green tea-based ingredients. Most tea and weight loss studies have tested tea components like the catechins and caffeine, so results may not be applicable to brewed tea. Some studies have shown that the green tea catechins may have a positive impact on weight loss. Other studies have found that drinking green tea for longer than six weeks may have a long term effect on weight loss. However, since tea is low calorie, if it replaces higher calorie beverages in someone's diet, a decrease in calories would also help promote weight loss. Regardless, tea isn't a magic wand for weight loss.
Blood Sugars
Multiple studies have shown that catechins in green tea significantly lowered fasting blood glucose levels and HgbA1c lab values. However, others have also shown that there is no significant decrease in any diabetic lab markers. However, drinking green tea does not appear to negatively impact diabetes management.
What is Matcha?
Matcha is a fine, green tea powder made from the green leaves of tea bushes. Matcha is the tea used in a Japanese tea ceremony. It's the only tea where the leaves are consumed as part of the drink. This means that the antioxidant content is higher than in other teas.
Image: Matcha Zen Blog What about caffeine?
The amount of caffeine in a given cup of tea depends on how long the tea is brewed. The average amount of caffeine in an 8oz cup of green tea is 25mg, which is about 1/3 - 1/2 the amount in one cup of coffee. No adverse side effects have been seen with intakes of caffeine less than 400mg. However, caffeine has a half life of 4-6 hours. This means that in 4-6 hours, only half of the caffeine has left your system. So if you're sensitive to caffeine, you may want to avoid drinking too much caffeine before bedtime.
Many people say that drinking caffeine will dehydrate you. Studies have shown that caffeine does not effect hydration up to 400mg per day. Tea can be just as hydrating as water, and contributes to daily water intake.
References:
Cochran N. "Green Tea: A Refreshing Beverage and Healthful Elixir." Today's Dietitian. 2016; 18(7): 29-31.
Ehrlich S. "Green Tea." University of Maryland Medical Center. Reviewed November 6, 2015. Available at http://umm.edu/health/medical/altmed/herb/green-tea. Accessed July 21, 2016.
Peterson J, Dwyer J, Bhagwat S, et al. Major flavonoids in dry tea. J Food Comp Anal. 2005;18(6):487-501.
Zheng XX, Xu YL, Li SH, Hui R, Wu YJ, Huang XH. Effects of green tea catechins with or without caffeine on glycemic control in adults: a meta-analysis of randomized controlled trials.Am J Clin Nutr. 2013;97(4):750-762.
Liu K, Zhou R, Wang B, et al. Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials. Am J Clin Nutr. 2013;98(2):340-348.
Wang X, Tian J, Jiang J, et al. Effects of green tea or green tea extract on insulin sensitivity and glycaemic control in populations at risk of type 2 diabetes mellitus: a systematic review and meta-analysis of randomised controlled trials. J Hum Nutr Diet. 2014;27(5):501-512.
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