Benefits of green tea: science and myths
Tea drinking, particularly green tea, has always been associated, at least in East Asia cultures (mainly in China and Japan) with health benefits. Only recently, the scientific community has begun to study the health benefits of tea consumption, recognizing its preventive value in many diseases.
Green tea benefits in preventing cancer
Several epidemiological and laboratory studies have shown encouraging results with respect to possible preventive role of tea, particularly green tea and its catechins, a subgroup of flavonoids (the most abundant polyphenols in human diet) against the development of some cancers like:
- oral and digestive tract cancers;
- lung cancer among those who have never smoked, not among smokers.
Tea polyphenols, the most active of which is epigallocatechin-3-gallate (EGCG), seem to act not only as antioxidants, but also as molecules that, directly, may influence gene expression and diverse metabolic pathways.
Green tea and cardiovascular disease
Cardiovascular disease is the main cause of deaths worldwide, particularly in low- and middle-income countries, with an estimate of about 17 million deaths in 2008 that will increase up to 23.3 million by 2030.
Daily tea consumption, especially green tea, seems to be associated with a reduced risk of developing cardiovascular disease, such as hypertension and stroke.
Among the proposed mechanisms, the improved bioactivity of the endothelium-derived vasodilator nitric oxide (NO), due to the action of tea polyphenols that enhance nitric oxide synthesis, and/or decrease superoxide-mediated nitric oxide breakdown seem to be important.
Green tea and antioxidant properties
Tea polyphenols may act, in vitro, as free radical scavengers.
Since radical damage plays a pivotal role in the development of many diseases such as atherosclerosis, rheumatoid arthritis, cancer, or in ischemia-reoxygenation injury, tea polyphenols, particularly green tea catechins, may have a preventive role.
Green tea benefits in weight loss and weight maintenance
- weight loss, by increasing energy expenditure and fat oxidation;
- weight maintenance, ensuring a high energy expenditure during the maintenance of weight loss.
- they are not able to induce a significant weight loss in overweight and obese adults;
- they are not helpful in the maintenance of weight loss.
Green tea and preventing dental decay
Animal and in vitro studies have shown that tea, and in particular its polyphenols, seems to possess:
- antibacterial properties against pathogenic action of cariogenic bacteria, as Streptococcus mutans, particularly green tea EGCG;
- inhibitory action on salivary and bacterial amylase (it seems that black tea thearubigins and theaflavins are more effective than green tea catechins);
- it is able to inhibit acid production in the oral cavity.
All these properties make green tea and black tea, beverages with potential anticariogenic activity.
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