There have been numerous reports in the media about the health benefits of drinking green tea. From cancer reduction, to weight loss, to general health, green tea has been promoted as an all round wise health decision. But let’s drill a little deeper and look at the role of green tea in cancer prevention if any.
What is Green Tea
Green tea is simply leaves of Camellia sinensis plant that have undergone minimal oxidation during their harvesting and packing process. The tea has been popular in China and throughout many Asian countries for many thousands of years and has become more commonly drunk in Western countries in recent years, largely because of the oft-mentioned health benefits.
Green tea and green tea extracts can also be used in other food products and cosmetics where it has a potential positive effect also. The extracts from Green tea can be found in many commercial products, but sometimes the product is so diluted and processed that the mention of Green tea is more of a marketing exercise than it is a legitimate additive for health reasons. Rates of cancer are lower in many Asian countries than they are in the West, and many researchers and health specialists suggest this is largely because of the role green tea plays in the Asian diet.
Green Tea’s Health Benefits
Some of the often mentioned benefits of Green tea include:
- A boost to the human immune system
- A way to remove toxins in the body
- Assists in the treatment of existing cancers in combination with traditional medicine
- Improves energy levels and overall health
- Can help you lose weight
- Is a viable alternative therapy for cancer treatment
But are these benefits accurate?
At this stage there is some evidence that Green tea might reduce the risk of getting cancer, but there is not sufficient evidence to suggest that green tea can cure existing cancers.
What research has told us is that green tea can reduce the risk of heart disease and only certain types of cancer. When researchers looked at the weight reduction properties of green tea they found that while it does not raise the metabolic rate in humans, some green tea extracts with polyphenols have been shown to increase the rate of fat oxidation.
Green tea is packed full of flavinoids, much more so than many other foods that are considered extremely healthy. Flavinoids have a well documented anti-oxidative and anticarcinogenic function in the human body which is a good thing, but the levels of flavinoids can vary dramatically depending on the quality of the green tea.
Researchers have also identified an extract in green tea called epigallocatechin-3-gallate (EGCG). That extract is also of great interest in cancer research and it’s exact role is still being established.
In the laboratory, cell studies have shown that some green tea extracts can prevent cancer cells from growing. The polyphenols and another substance called catechins have anti-oxidant properties and prevent the cancer cells growing. Keep in mind that these kinds of cell studies are very different to human studies which see if the chemicals in their diluted form can still play a role in stopping the growth of cancer.
The human studies we have seen so far are a mixed bag. In a meta study (which looks at the results of many other studies) in 2006 discovered that green tea can lower the risk of breast cancer. However other meta studies have not found enough evidence to back this up.
The same is true for bowel cancer, with one study suggesting that green or black tea played a role in the reduction of risk of bowel cancer, then another study finding no such link.
One Chinese study found that men who drank green tea on a daily basis had half the risk of stomach cancer as those who did not. A 2008 meta analysis which reviewed 43 of studies suggests that the evidence of reduced risk is only small. Many studies suggest it reduces risk while many claim to have found no link between green tea consumption and the reduction in risk of stomach or digestive tract cancers.
Other forms of cancer have no apparent link, with studies into prostate cancer seeing no link between green tea consumption and reduced risk.
One problem with the studies is that many don’t factor in lifestyle factors and investigate the affects of green tea on a narrow section of population. Additionally, in many cases the studies don’t detail the amount of green tea taken, nor the quality of the green tea (which plays a substantial role).
Some trials have shown more positive results though, and none of the trials have shown negative effects shown with the moderate consumption of green tea. Green tea in large quantities has the same negative and positive effects associated with the consumption of caffeine – an increase in anxiety or nervousness, trouble sleeping.
One of the trials that has shown more positive results was a 2012 study into the ability of a green tea extract to help treat cancer. Polyphenon E was given to 45 chronic leukemia patients who were not taking any other treatment for the disease. 30% of patients had a positive effect from the green tea and saw their lymph nodes shrinking and a reduction in the number of cells with leukemia. A small trial yes, but it shows some promise with green tea extracts.
Drinking Green Tea
Green tea is a very safe drink to consume. The only drawback with consuming green tea is the small amount of caffeine present that causes irritability, nervousness and more frequent urination.
Many health specialists suggest that you drink between 3 and 5 cups of green tea per day to obtain a health benefit. The level of caffeine is about 30% of the caffeine content of a cup of instant coffee. So 3 cups a day is the equivalent of 1 cup of coffee in the morning. You can obtain decaffeinated green tea, but some experts suggest that the additional processing to remove the caffeine may have a negative effect.
Green tea capsules are also available and you can even add green tea to food!
Before consuming green tea, if you are on any medications consult with your doctor to determine side effects. Green tea is mostly harmless, but for people with heart conditions, the additional caffeine may be a factor. Always consume green tea in moderation to avoid any issues with excessive caffeine.
In very rare cases, green tea can affect how well you absorb certain medications, so that is worth looking into before you begin consuming it.
Green Tea Claims
So there is the evidence. It may be helpful in preventing cancer, and green tea extracts may have a role in treating cancer, but the research is far from clear.
Be wary of any websites that are selling green tea as a cure for cancer or some kind of magical tool for weight loss. This is inaccurate.
The evidence that green tea consumption is a great source for anti-oxidants is much more clear and if you want to maintain good overall health as well as potentially reduce cancer risk, it is a great choice.