Tea and health

2013-10-01

The ability of tea polyphenols to bind with dietary fat can reduce fat absorption along the digestive tract.

Tea has long been well-recognized for its medicinal and recreational purposes in Chinese history while only mounting research over the past few decades has shed lights on its potential use in disease prevention and management, in particular cancer, overweight and cardiovascular disease. Tea can be categorized into green tea, oolong tea and red tea depending on the degree of tea leaf processing.

Tea in cancer prevention

Polyphenols, found in all kinds of tea in different amount and combination, have been shown beneficial to our health due to its strong antioxidant activity. This activity can be best demonstrated by catechins, a type of polyphenols, in green tea. It can scavenge reactive oxygen reactive oxygen species and free radicals to prevent our body from oxidation damage. Although the ability to prevent other cancer prognosis remains questionable, in numberous animal studies, it did exhibit anti-tumor and anti-cancer properties along the digestive tract. O obtain the most catechin in tea, it is noteworthy that green tea with the least processing has the richest amount of catechins, while the least in red tea as it can be destroyed during intensive tea leaf processing such as fermentation for red tea leaf production.

Tea in weight management

The key element in tea for weight control has been controversial. A Chinese study examined the effect of tea consumption on weight among 182 moderately overweight people. The results revealed the reduction of fat mass and body fat percentage in the group consuming 1772 mg of catechins a day, equivalent to a minimum of 6 cups of green tea, for 3 months. This study has brought extensive argument on whether the effect is due to polyphenols or caffeine in tea. While one side suggests that the ability of tea polyphenols to bind with dietary fat can reduce fat absorption along the digestive tract and thus lower calorie intake and body fat deposition, the other side believes that it is just one of the tricks played by caffeine. Some others think it is a consumption of two. Despite the inconclusive discussion on these chemicals, swapping sugary beverages with unsweetened tea drinks can create a reduction of calorie intake which is the basis of weight management.

Extensive research has shown the benefit of tea consumption, especially green tea and oolong tea, in the risk reduction of cardiovascular disease. A large scale study in Japan involving 76979 people aged 40-79 found that 6 cups of green tea a day can lower cardiovascular mortality. In China, a case control study also reported the reduction in stroke risk among people consuming green and oolong tea. How about red tea? Its evidence in lowering the risk is rather weak. Anyway, this cardiovascular protective property of tea is believed to be due to its capability of lowering blood lipids. For example, catechins can reduce cholesterol production as well as possess anti-inflammatory and anti-clotting properties. 

The downside of drinking tea

While tea is a good recreational beverage alternative to water, people with special needs and conditions may need to be aware of several downsides of its consumption. Vegetarians and pregnant women are advised to consume tea in-between meals at moderation as polyphenols and phytic acid, another chemical in tea, can potentially reduce the absorption of non-haem iron present in plant based foods. Kids as well as people suffering from insomnia are also recommended to minimize tea consumption due to the arousal effect of tea caffeine, whereas people constantly suffering from gastric pain or discomfort should eat before or while drinking tea to avoid any discomfort induced by tea stimulants.

All in all, tea drinking can bring us joyful experience with numerous potential benefits, not to mention the role of catechins in blood glucose and blood pressure management. However, excessive green tea supplement may not only counteract the benefits, but also upset liver function which may pose a great impact on our health. Therefore, drinking tea would be a safe way to go!

References:

1. Yang CS, Wang H, H, Li GX, Yang Z, Guan F, Jin H. 2011. Cancer prevention by tea: evidence from laboratory studies. Pharmacol. Res. 64:113-22

2. Yuan JM, Sun C, Butler LM. 2011 Tea and cancer prevention: epidemiological studies. Pharmacol. Res. 64:123-35

3. Wang H, Wen Y, Du Y, Yan X, Guo H, et al. 2010. Effects of catechin enriched green tea on body composition. Obesity (Silver Spring) 18:773-79

4. Hursel R, Viechtbauer W, Dulloo AG, Tremblay A, Tappy L, et al. 2011. The effects of catechin rich teas and caffeine on energy expenditure and fat oxidation: a meta-analysis. Obes. Rev. 12:e573-81

5. Mineharu Y, Koizumi A, Wada Y, Iso H, Watanabe Y, et al. 2011. Coffee, green tea, black tea and oolong tea consumption and risk of mortality from cardiovascular disease in Japanese men and women. J. Epidemiol Community Health 65:230-40

6. Deka A, Vita JA. 2011. Tea and cardiovascular disease. Pharmacol. Res. 64:136-45

7. Ogunleye AA, Xue F, Michels KB. 2010. Green tea consumption and breast cancer risk or recurrence: a meta-analysis. Breast Cancer Res. Treat. 119:477-84

8. Yuan JM, Sun C, Butler LM. 2011. Tea and cancer prevention: epidemiological studies. Pharmacol. Res.64:123-35

9. Chung S. Yang and Jungil Hong 2013. Prevention of chronic diseases by tea: possible mechanisms and human relevance. Annu. Rev Nutr 2013.33:161-181

330 Tips provided by:  Ms Grace Lam  (Senior Dietitian - Centre for Nutritional Studies, School of Public Health and Primary Care, Faculty of Medicine, CUHK)