Tea is the world’s most popular beverage second only to water. Across the country, restaurants and coffee shops are serving up premium freshly brewed teas, while supermarkets, convenience stores and vending machines are purchasing more and more bottled tea. According to the Tea Association of the USA, 160 million Americans consume tea and in 2012, 2.25 billion dollars were spent on tea in the US.
We are drawn to tea not only for its delicious flavors and capacity to sooth, but also because of the buzz on its many health benefits.
Types of Teas
The classic definition of tea is an infusion of the leaves from the Camellia sinensis plant. This evergreen shrub is native to East and South Asia and was first consumed over 3000 years ago in China. The different types of processing of this plant create different varieties of tea.
Root teas (kudzu), spice teas, (chai) yerba mate, and herbal teas do not fit the classic definition of tea. Herbal teas are infusions of herbs or plants other than Camellia sinensis. They have become popularized due to several medicinal claims, some lacking supportive evidence. There are mixed opinions on the safety of herbal teas for both, especially during pregnancy. Due to lack of research the FDA encourages caution for pregnant women consuming herbal teas.
One of the key steps in the tea making process is the degree of fermentation the tea leaves are allowed to undergo. Fermentation refers to the enzymatic oxidation of the leaves. This process can be stopped by applying heat, either pan-frying or steaming the tea leaves, before they are completely dried out. The amount of fermentation varies among green, black, white, and oolong tea.
Phytochemicals
Tea is rich in bioactive compounds called phytochemicals. The primary phytochemicals found in tea include flavonoids and catechins, which contribute to the health benefits that tea provides including vasodilation, improving blood flow to the brain and greater insulin sensitivity. The phytochemical content in tea varies due to the different degrees of fermentation; fermentation changes the types of phytochemicals found in tea. The phytochemical profile influences the flavors, aroma, and colors of teas.
Bottled or Brewed?
Evidence shows that bottled tea contains fewer phytochemicals than a single cup of freshly brewed green or black tea. Some bottled teas contain such small amounts that consumers would have to drink 20 bottles to get the phytochemicals present in one cup of tea. This might be because of the quantity and quality of tea used to prepare a batch and the tea brewing time. Some phytochemicals can taste bitter, therefore it is common for manufacturers to add less tea and more water, which makes the phytochemicals content low, but the taste smoother and sweeter.
White Tea
This tea is the least fermented of the teas. Young leaves and buds are simply steamed and dried. White teas undergo very light fermentation during the withering process.
Green Tea
This tea is minimally fermented- the leaves are picked, dried, then heated in order to stop fermentation (or stop the exposure to oxygen).
Oolong Tea
Made from young tea leaves and leaf buds fermented a little less than black tea, but still much more than green tea, about 45 minutes after having been wilted in the sun.
Black Tea
This tea is fully fermented and has the highest amount of caffeine of all the teas. It is withered, rolled, then fermented before being dried, which makes it black
Caffeine Content of Classic Teas
Caffeine content varies between different types of teas. It is primarily influenced by factors such as brewing time, the amount of tea and water used for brewing, and whether the tea is loose-leaf or bagged tea. The caffeine content of tea generally contains about half the amount of caffeine found in coffee, but contains more caffeine than 8 oz of cola.
| Beverage | Caffeine (per 8 oz) |
|---|---|
| Brewed Coffee (from grounds) | 95 mg |
| 1 shot of Espresso | 1 oz = 64 mg |
| Cola | 22 mg |
| Green tea | 44 mg |
| Black tea | 47 mg |
Benefits
Heart Health
Various studies have examined the relationship between tea consumption and cardiovascular disease. Some research has found no association between drinking tea and cardiovascular disease risk, but other studies found that drinking at least three cups a day of black tea may be associated with a modest decreased risk of myocardial infarction. A recent study examined 40,530 Japanese adults. The participants that drank five or more cups of green tea per day had a 26% reduction in mortality from cardiovascular diseases. Overall, green and black tea may be protective of cardiovascular diseases, but more research needs to be conducted to draw any definite conclusions.
Cancer Prevention
Research suggests that the catechins in green and black tea may play a role in preventing cancer. Since 2006, more than 50 epidemiologic studies have been published; examining the relationship between tea consumption and cancer risk. The results of these studies are often inconsistent, but some have linked tea consumption to reduced risk of cancers of the colon, breast, ovary, prostate, and lung. The inconsistent results may be due to variables such as the methods of tea production, the types of tea studied, or the genetic variation in how people respond to tea consumption.
Tea for Teeth
In 2010, Japanese researchers reported at least one cup of green tea per day was associated with significantly decreased likelihood of tooth loss. Fluoride is found in tea leaves. The fluoride levels found in green, oolong, and black teas are found to be safe and preventative of dental cavities.
Diabetes Prevention
Most research has linked green or black tea or compounds in tea to improved blood sugar control or reduced risk of type 2 diabetes. For instance, a 2012 study in BMJ Open looked at data from 50 countries and found that high consumption of black tea was strongly associated with a reduced diabetes risk. And a 2013 Chinese meta-analysis of clinical trials suggested that green tea helps reduce blood sugar.
Drink it or Supplement?
Evidence supporting tea as a weight-loss aid is based mostly on studies that have used green tea extracts, not necessarily the tea itself. Some studies have found that these extracts have the potential to influence body weight and composition through fat oxidation. However, there is not enough evidence to conclude that these extracts are safe or if drinking tea has the same effect as ingesting the extracts.
A green tea supplement or pill is not recommended or regulated by the FDA. It is not known if they hold any benefits or if they are safe. In some cases, green tea pills can interact with certain medications, and there are concerns about potential liver damage with supplemental use. Some, particularly those marketed towards weight loss, may contain very high doses of caffeine. Common side effects of green tea extracts include nausea, vomiting, abdominal pain, and diarrhea. These are likely due to the caffeine content
Metabolism Myth: Green tea speeds metabolism
Unfortunately, no magic food will speed up your metabolism. Some studies have shown that green tea can temporarily boost metabolic rates, but the increase isn’t enough to offset eating too many calories.
What is Kombucha?
What is all this talk about kombucha? It is a “trendy” new drink found in health or specialty food stores. It is not as new as it may seem though. Kombucha was first consumed during the Tsin Dynasty in China in 221 BC. It is essentially a fermented drink made with tea, sugar, and a bacterial yeast culture. Health claims include improving digestion, preventing cancer, and stimulating the immune system, but none of these claims have been backed with research.
References
- Cochran, N. (2014, February 4). The Health Benefits of Tea.
- Dulloo, A., Duret, C., & Rohrer, D. (1999, December 1). Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans.
- Higdon, J., & Drake, V. (2008, January). Tea. Linus Pauling Institute of Micronutrient Research for Optimum Health.
- Marcason, W. (Ed.). (2014, January 31). Metabolism Myth and Facts.
- Herbal Tea and Pregnancy. (2013, January 1).
- Meadows, C. (2011, June 29). Health Benefits of Kombucha Tea (pdf).
- Tea Benefits: A Research Wrap -Up. (2014, February 7).
- Tea and Cancer Prevention: Strengths and Limits of the Evidence. (2010, November 17).
- Bottled Tea Beverages may Contain Fewer Polyphenols Than Brewed Tea. (August 22, 2010).