Researchers from the University of Minnesota have performed a meta-analysis of 13 studies and concluded that green tea consumption lowers the risk of breast cancer. The details of this report appeared in the November 2005 issue of Carcinogenesis .[1]

Experimental studies have shown that tea and tea polyphenols have anti-carcinogenic properties against breast cancer. In a previous study, Researchers from the University of Southern California reported that a high intake of green tea or soy products was associated with a significant reduction in the incidence of breast cancer in Asian American women.[2] This case-control study found an independent effect of both soy and green tea.

The effect of soy products is thought to be due to phytoestrogens. Phytoestrogens are plant-derived non-steroidal compounds found in soy products, unrefined grain products, carrots, spinach, broccoli and other fruits and vegetables. Phytoestrogens have a weak estrogen-like effect and are protective against various cancers. The best documentation appears to be for the prevention of breast and prostate cancer, which are hormone-dependent cancers. This study was helpful in demonstrating that both green tea and soy products independently lowered the incidence of breast cancer. An effect of green tea on the incidence of other cancers such as stomach and colorecatal has not been demonstrated. A recent review of 8 studies suggests that drinking 5 or more cups of green tea a day can lower the incidence of stage I-II breast cancer.[3] This study concluded that the data on green tea ingestion and recurrences in women with breast cancer was too incomplete to make any conclusions. However, green tea intake in one study had no impact on progression of prostate cancer.

Meta-analyses of 13 studies showed that women who had the highest intake of green tea had a 22% reduction in risk of developing breast cancer compared to women with the lowest intake. They also reported that black tea ingestion was more problematic with some studies showing a slight decreased risk and others showing an increased risk with high intake.

Comments:  These studies suggest a modest preventative effect of ingesting relatively large quantities of green tea in preventing breast cancer. However, only controlled randomized trials can confirm these observations and they are unlikely to be performed. Fortunately, there is no apparent harm from drinking green tea.

Related news:

Green Tea Does Not Appear Effective for Treating Androgen Dependent Metastatic Prostate Cancer (5/2/2002)

Green Tea Does Not Appear to Prevent Stomach Cancer (2/12/2002)

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