This ancient beverage is steeped with flavor and numerous health benefits.
One reason why so many consumers are switching to tea is its reputed health benefits. This article will examine some of the studies indicating that tea may improve heart health and reduce the risk of certain diseases, such as diabetes.
It should be noted that herbal teas are not derived from the Camellia sinensis plant and are thus not the same as traditional teas. Because herbal teas are combinations of the leaves, roots, bark, seeds and flowers of other plants, they are not thought to bestow the same health benefits as conventional tea.
Tea flavonoids have been credited with helping protect the human immune system and reducing the risk of various diseases, including cardiovascular disease (CVD), bone and oral diseases, diabetes and certain cancers. The antioxidant properties of tea flavonoids are believed to fend off free-radical damage to cells, which can lead to many chronic diseases in the body. An average cup of brewed green or black tea contains 150–200 milligrams (mg) of flavonoids (Merken & Beecher 2000).
With the Dietary Guidelines for Americans 2005 recommending that the public consume more plant-based foods, such as fruits and vegetables, nutrition experts contend that tea should be included among those foods. “Tea is a plant food and almost exclusively a catechin beverage,” notes Blumberg.
Findings from a prospective cohort study of 8,552 general residents of Saitama Prefecture, Japan, revealed that drinking more than 10 cups of green tea per day (versus less than 3 cups per day) significantly reduced death rates from cancer (Nakachi, Eguchi & Imai 2003). In other research, black tea was found to boost the immune system in animals with cancer, and like anticancer drugs, did not promote the proliferation of cancerous cells at the same time (Bhattacharyya et al. 2004).
Studies have also indicated that tea may help reduce the risk of ovarian cancer. In a Chinese study, researchers found that the risk of this type of cancer declined when participants increased the frequency and duration of their overall tea (especially green tea) consumption (Zhang, Binns & Lee 2002). Likewise, green and black tea consumption was linked to decreased ovarian-cancer risk in a large, long-term, population-based study of 61,057 Swedish women aged 40–76 years old (Larsson & Wolk 2005). Over the course of a 15-year follow-up, those women who drank two or more cups of tea daily had a 46% lower risk of ovarian cancer compared with those who drank no tea at all. Even the slightest tea intake (< 1 cup per day) was linked to an 18% reduction in risk, while 1 cup per day decreased the risk of ovarian cancer by 24% (Larsson &Wolk 2005)
Evidence indicates that the antioxidant properties of tea flavonoids may help lower CVD risk by decreasing lipid oxidation (Weisburger 1999); may reduce the incidence of heart attacks and stroke (Hertog et al. 1993; Keli et al. 1996); and may beneficially impact blood vessel function (Duffy et al. 2001).
Recent data from The Ohsaki National Health Insurance Cohort Study revealed a cardiovascular benefit among green-tea drinkers, especially in women. The data showed a 16% lower risk of all-cause and CVD mortality over 11 years of follow-up in participants who consumed five or more cups of tea per day, with the inverse association being more prevalent in female subjects (Kuriyama et al. 2006). The researchers’ rationale for the mortality outcome differences between the genders was cigarette-smoking rates. Men were more likely to smoke, and the inverse associations between green-tea consumption and CVD mortality appeared to be more pronounced in participants who had never smoked.
One large cohort study involved 17,413 middle-aged and older men and women in 25 communities across Japan. The researchers found that participants who consumed six or more cups of green tea per day actually lowered their risk of diabetes by 33% (compared with those who consumed none) (Iso et al. 2006). There appeared to be a dose-response relationship: in other words, the more caffeine the participants consumed, the lower their risk level was for diabetes. The subjects in this study had a median caffeine intake of 416 mg a day from both green tea and coffee (Iso et al. 2006).
Although this research focused on the caffeine in green tea, it should be noted that plants containing flavonoids have long been used to treat diabetes in Indian medicine (Waltner-Law et al. 2002).Green-tea flavonoids have been shown to have insulin-like activity, as well as insulin-enhancing activity (Cheng 2006a; Anderson & Polansky 2002; Cheng 2006b).
“Although there has been some experimental work on tea’s effects on insulin sensitivity, the research is in the early stages,” explains Blumberg. Even though the research has not indicated a standard recommendation for tea as an antidiabetic agent, experts contend that more is better—as is the case with all plant-based foods.
The Beverage Guidance System proposed recently in the American Journal of Clinical Nutrition (www.beverageguidancepanel .org), recognizes this dose-response relationship (i.e.more is better) by suggesting that water, tea and coffee be the major contributors to our daily fluid intake (Popkin et al. 2006). The guidelines recommend up to eight servings of unsweetened tea per day because tea is virtually calorie-free, delivers antioxidant phytonutrients and has less caffeine than coffee (about 40 mg per serving) (Popkin et al. 2006).
“Remember, when people drink tea instead of something else (namely sugar-laden, high-calorie juice drinks and/or soda), it will make them feel more full and satisfied with zero calories,” Nussinow advises.
“The state of the science is mixed (on this),” according to Blumberg. However, Blumberg does point out that if the health benefits of tea are based on a dose-response relationship, then diluting tea with milk would equate to a smaller quantity of catechins being ingested—and thus fewer benefits overall.
And do think twice before you go heaping teaspoons of sugar into your cup of tea. While sweetened tea is a staple of the American South, most people now realize that the addition of sugar to any beverage or food simply amounts to useless calories and potential dental problems. If unsweetened tea simply isn’t for you, consider adding a small amount of sweetener to the brew.
For more tips on healthy ways of serving tea, see “Hot Tips for Making Hot Tea,” sidebar.
There are three basic things to remember when making hot tea: quality, temperature and time.
1. Quality: Use only purified, filtered water.
2. Temperature: To avoid an astringent taste, the water for black tea should be just at the boiling point, while for green tea the water is better slightly below boiling (no more than 180 degrees Fahrenheit, or around 80 degrees Celsius).
3. Time: Steep tea for at least 3 minutes to get the maximum antioxidant content.
Victoria Shanta Retelny, RD, LD, is a food and nutrition communications consultant based in Chicago. She is a graduate of the Roy H. Park School of Communications at Ithaca College in New York and also of Loyola University’s food and nutrition program.
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