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- 4.2. Breast cancer
- 4.3. Pancreatic cancer and ovarian cancer
- 4.4. Prostate cancer
- 4.5. Lung cancer
4. EPIDEMIOLOGICAL STUDIES4.1. Gastrointestinal cancerThe incidence of gastrointestinal cancers has risen rapidly over the past three decades in the United States and northern Europe. Early correlative and cohort studies indicated that tea consumption either negatively or positively associated with stomach cancer (45). In a population based case-control study conducted in Taixing, Jiangsu province of China, green tea reduced the risk of developing stomach cancer by 81% and esophageal cancer by 39% in alcoholics. It also reduced the incidence of stomach cancer by 16% and esophageal cancer by 31% among cigarette smokers (46). In a case-control study conducted in China, drinking green tea was found to reduce the risk of esophageal and gastric cancers (47). 4.2. Breast cancerWorldwide, breast cancer is the most commonly diagnosed cancer in women representing 16% of all cancers and its incidences continues to increase. It has been suggested that tea consumption reduces the risk of mammary cancer. In a population-based case-control study of breast cancer in Chinese, Japanese and a Filipino-American woman, the risk of breast cancer was found to be considerably reduced by intake of green tea (48). A population-based cohort study of 74,942 Chinese women suggests that regular drinking of green tea may delay the onset of breast cancer. In terms of breast cancer prevention, the studies are inconclusive. In one large study, researchers found that drinking tea of any type was not associated with a reduced risk of breast cancer. On the other hand, when the researchers broke down the sample age of women under 50, those who consumed 3 or more cups of tea per day were 37% less likely to develop breast cancer compared to women who didn’t drink tea. Wu et al reported that women who possessed at least one low activity COMT allele have an inverse association between tea intake and breast cancer risk. In contrast the women who were homozygous for high activity COMT allele, a risk of breast cancer did not differ between tea drinkers and non tea drinkers (49). 4.3. Pancreatic cancer and ovarian cancerPancreatic cancer is one of the most aggressive and treatment-refractory malignancies in humans. In one clinical study researchers compared non-drinkers of green tea with drinkers and found that those who drink green tea regular were significantly less likely to develop pancreatic cancer. A population-based cohort study was conducted in Japan to investigate the substantial impact of green tea or coffee consumption on pancreatic cancer risk in general (50). However, it is not clear from this population-based study whether green tea is solely responsible for reducing pancreatic cancer risk. Ovarian cancer is prevalent in industrialized nations, with the exception of Japan. In the United States, females have a 1.4% to 2.5% (1 out of 40-60 women) lifetime chance of developing ovarian cancer. A population-based Swedish Mammography Cohort study demonstrates that tea consumption is associated with a reduced risk of epithelial ovarian cancer in a dose-response manner (51). An interesting clinical study conducted in China found that women with ovarian cancer who drank at least one cup of green tea per day survived longer than those who were not green tea drinkers (52). 4.4. Prostate cancerThe second leading cause of cancer deaths among men in the Western countries is prostate cancer. Many factors, including genetics and diet, have been implicated in the development of prostate cancer. Over the last two decades various epidemiological studies have suggested that green tea consumption correlates with lower risk of prostate cancer. Similarly, the prostate cancer risk declined with increasing frequency, duration, and quantity of green tea consumption in case-control study conducted in southeast China (53). However, of two cohort studies investigating the risk of prostate cancer, one found no association between green tea consumption and prostate cancer risk (54) whereas the other found a positive association (55). Recently, a large cohort study was conducted in Japan found that drinking >5 cups of green tea per day showed reduced risk of developing advanced cancer compared to those having 1 cup per day. Three other cohort studies have been also performed by the same group and found no statistically significant effect in reducing the risk of prostate cancer (56). These studies suggest that a well-designed intervention trial may be able to provide a clear demonstration about the possible cancer-preventive effect of tea polyphenols (see section 7.1. Chemoprevention trials) 4.5. Lung cancerLung cancer is one of the deadliest forms of cancer in both men and women in terms of incidence. In vitro green tea polyphenols have been shown to inhibit the growth of human lung cancer cells. A few clinical studies have investigated the link between green tea consumption and lung cancer in people and these studies have been conflicting. On the association of tea and lung cancer, around 20 studies were published, including 6 cohort studies. Two of the cohort studies used data for cancer mortality instead of incidence. The overview of all studies on tea and lung cancer is fairly symmetrical, although it appears slightly skewed toward a protective association of tea intake. When tea intake and lung cancer were studied among never- or former smokers to eliminate the confounding effect of smoking, 4 of 7 reported associations were significantly protective. Well-designed cohort studies, in particular for catechins, are needed to strengthen the evidence on the effects of long term exposure to physiological doses of dietary flavanoids. Another population-based cohort study in Japan among 41,440 men and women, aged 40-79 years, found no evidence that green tea consumption is associated with lung cancer (57). жүктеу/скачать 1.88 Mb. Достарыңызбен бөлісу:
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