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Setembro / 2004
Tea and Cancer
Tea Consumption and Cancer Incidence in a Prospective Cohort Study of Postmenopausal Women
Zheng, W., et al. American Journal of Epidemiology, 144(2):175-182, 1996.
A prospective cohort study of 35,369 postmenopausal Iowa women showed that drinking black tea may protect against cancers of the digestive and urinary tracts. Women who reported drinking 2 or more cups of tea per day had 40 to 70 percent lower incidence rates of these cancers compared to women who never or infrequently drank tea. In addition, black tea consumption was related to a slight, though not statistically significant, reduced incidence of all cancers combined. No appreciable association of tea drinking was found with melanoma, non-Hodgkin´s lymphoma or cancers of the pancreas, lung, breast, uterine corpus or ovary. The authors conclude that tea, as one of the most popular beverages consumed worldwide, may protect against some cancers in postmenopausal women.
Tea and Cancer Prevention: An Evaluation of the Epidemilogic Literature
Kohlmeier, L., et al. Nutrition and Cancer, 27(1):1-13, 1997.
According to this literature review, animal and in vitro data indicate a potential antioxidant effect of tea components. In contrast, the epidemiological evidence for a protective effect of tea on cancer risk is inconsistent. Studies indicate that green tea is associated with decreased risk of colon cancer, but the effects of either green or black tea at other sites is unclear. Limitations of the studies in terms of the categorization of tea consumption, choice of control groups, and inadequate control for confounding variables may have obscured possible relationships between tea drinking and reduced cancer risk. The potential benefits of tea drinking may be restricted to high consumption levels in populations at high risk for specific cancers.
Tea in Chemoprevention of Cancer: Epidemiologic and Experimental Studies (review)
Katiyar, S. and Mukhtar, H. International Journal of Oncology, 8:221-238, 1996.
This comprehensive review summarises the current epidemiological and experimental data on tea and cancer. While the majority of experimental studies on the potential chemopreventive effects of tea have used green tea, several key studies have included black tea. A protective effect of tea has been demonstrated in specific bioassay models for cancer of the lung, forestomach, oesophagus, duodenum, pancreas, liver, breast and colon. In addition, it appears that tea protects against ultraviolet radiation-induced skin tumorigenesis in animal and skin tumour model systems. A number of epidemiologic studies suggest a negative association between tea drinking and cancer risk. The authors conclude that although a considerable body of research has accumulated on the preventive effect of tea on cancer, a clear understanding of the mechanisms by which tea prevents growth and progression of specific cancers is needed. More research on black tea and its components is critical, as well as studies on the absorption, distribution and metabolism of tea in human populations.
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