The truth about green tea

Updated June 20, 2018

Websites across the Internet tout the benefits of green tea, for everything from slowing the aging process to helping fight various forms of cancer. Finding out the truth isn’t easy, because most information you can find plays up the positives studies without acknowledging any negative results or inconsistencies. If you want to know if green tea really can help you, you have to think about it from a scientific perspective. Four of the main benefits attributed to green tea are its cancer fighting abilities, its use for heart disease, regulating insulin in diabetes patients and helping people lose weight.

Why green tea?

There are three different types of tea, green, black and oolong, but only green tea is reputed to carry these major benefits. The reason for this is related to how it’s produced. Whilst black tea is fermented and oolong is partially fermented, green tea isn’t, which means it keep more of its polyphenols. These are powerful antioxidants, which fight free radicals and are therefore are believed to help with cancer, heart disease and even aging.

Free radicals: Cellular menace

Despite the wild and fun-loving name, free radicals actually have a pretty bad reputation. Higher numbers of them are associated with Parkinson’s disease, Alzheimer’s disease, cancer and cardiovascular disease. They are thought to roam around the body, breaking cell walls and damaging the DNA. This does happen – free radicals steal electrons from important molecules in the body and therefore cause them to break apart. This is undoubtedly a bad thing, and explains their negative associations.

Free radicals: The other side of the story

They aren’t all bad though. Your body is a pretty complicated piece of machinery, and it seems illogical that it would just let rogue chemicals damage vital cells for no reason. Free radicals actually play a variety of important roles, such as fighting bacteria and turning oxygen and food into energy. Your immune system relies on them, so going on an all-out antioxidant binge to rid yourself of them isn’t necessarily that wise. The role of antioxidants – such as the polyphenols found in green tea – isn’t clearly understood by science, but they do seem to have some benefits.


The two cancers that are most likely to be helped by green tea consumption (according to studies) are bladder cancer and breast cancer. In the research done into both of these areas so far, it has been shown that green tea consumption both reduced the risk of developing cancer and improved survival rates. However, the risk of developing most other cancers studied, including colorectal, oesophageal and lung cancer, could either be reduced or increased, according to different studies. Much more research is needed into the area.

Heart disease

Population-based studies have indicated that green tea might be helpful for the prevention of heart disease. These studies follow large groups of participants or use existing data to determine the effect green tea has on the likelihood of developing heart disease. Although researchers are unsure why, the tentative suggestion is that because it lowers triglyceride and cholesterol levels, green tea does reduce the risk of heart disease. It’s estimated that three cups per day lowers your chance of developing the condition by 11 percent.


The research on green tea’s effects on diabetes is limited, and also can be contradictory. Whilst some studies do show that it can prevent type one diabetes and slow its progression, there are also conflicting results. This is another area in which more research is clearly needed, because some studies show no benefits to insulin levels at all.

Weight loss

One area where the benefits of green tea are more strongly supported is weight loss. It does this primarily though speeding up metabolism, reducing the numbers of “bad” LDL cholesterol and increasing the numbers of “good” HDL cholesterol. This effect also clears out the arteries, which generally improves their function.

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About the Author

Lee Johnson has written for various publications and websites since 2005, covering science, music and a wide range of topics. He studies physics at the Open University, with a particular interest in quantum physics and cosmology. He's based in the UK and drinks too much tea.