Green tea is one of the most commonly cited natural ways to reduce cancer risk, but how much evidence is there to support this claim?

Unfortunately, it is very difficult to assess this question due to the complexity of the problem. Cancer is not one disease, but a group of diseases that can occur at dozens of different locations throughout the body. Different risk factors are associated with different cancers, and it is unlikely that a single factor works alone to cause (or prevent) cancer at every site.

Additionally, cancer progresses through multiple stages, and different genetic and environmental factors are important at different stages of the disease. In other words, tumor formation could be initiated but may not progress further if additional factors are not present to promote the disease.

The same holds for preventative measures and treatments. Green tea, for example, may inhibit tumor growth and angiogenesis (the formation of blood vessels that feed the tumor) but not metastasis (the spread of cancer to other organs), and this may be different for different kinds of cancers. For these reasons, it is not surprising that most rigorous review studies assessing the role of green tea in cancer have shown conflicting results, without enough evidence to draw firm conclusions.

That said, there is a substantial body of evidence that green tea may help prevent cancer development in some cases. This includes rodent models, in vitro experiments, and some human studies. Notably, epidemiological (population) studies have been inconsistent, but this is likely due to confounding factors such as difficulties in measuring tea consumption, different risks among different populations, and differences in diet, exercise and other health-related behaviors. The quality of tea may also be a factor, and most studies show a stronger benefit of green tea than black tea.

Importantly, cancer is not the only disease where green tea may play a protective role. Tea has been associated with a reduced risk of heart disease through its antioxidant and lipid-lowering effects. Tea may also improve insulin resistance and protect against cognitive impairment and Alzheimer’s Disease.

To summarize, it is likely that green tea plays at least a minor role in the prevention and inhibition of some kinds of cancer. However, there are many potential confounders, and green tea alone is not likely to be sufficient to prevent tumor growth in most cases. But combined with a healthy diet and non-sedentary lifestyle, green tea may contribute significantly to prevention of cancer and other diseases.

When it comes to the science of wellness, distinguishing the facts from the urban legends can be tough. That’s why we’ve enlisted Darya Pino – a scientist, foodie, and self-proclaimed geek girl. Check out the ZocDoc Blog every Tuesday to see her bust the biggest myths in health.

Image: Afternoon Ritual, a Creative Commons Attribution (2.0) image from DaveFayram’s photostream.