Can Green Tea Help Prevent or Treat Breast Cancer?

Amongst all the talk about the benefits of drinking green tea in recent years are several claims that a chemical found in green tea—epigallocatechin-3-gallate (EGCG)—may be a powerful weapon against breast cancer. The low rate of breast cancer (and some other cancers) in regions where people drink large amounts of green tea is what made researchers start examining the relationship.

Before you put faith in your teacup, it's important to dig into the science—what's known and what needs more examination.

Antioxidants and Free Radicals

Green tea's cancer-fighting reputation comes from its polyphenols, which are chemicals that have antioxidant properties. Antioxidants protect the cells in your body from free radicals, highly reactive molecules that speed the damage caused by chemicals in the environment or by aging, and that can lead to the development of cancer (and other diseases).

Free radicals can damage tissues in many ways, one of which is by directly damaging DNA. Since damage to DNA (gene mutations) is what leads to the development of cancer, researchers have given a lot of attention to nutrients that can neutralize free radicals before they do their damage.

EGCG is one of the antioxidants found almost exclusively in green tea.

Use for Breast Cancer Prevention

Many studies have looked at the role of green tea and breast cancer prevention. Not all of them have found an association between drinking green tea and lower breast cancer risk, but some of the largest, most credible studies have.

In the Prostate, Lung, Colorectal, and Ovarian Screening Trial, which included more than 100,000 people, researchers found that those who consumed green tea had a lower overall risk of cancer; in other words, it appeared to reduce the risk of any cancer. Whereas some studies have looked at very large amounts of green tea—say, drinking 30 cups daily—this study looked at people who drank just one daily cup of green tea.

A 2017 study looked at breast density in women given a supplement of EGCG for one year. High breast density is linked with an elevated risk of breast cancer. While the supplement didn't change breast density in older women, it significantly decreased it in young women. The effect was similar to that of tamoxifen, a drug that's sometimes used to reduce the risk of breast cancer in high-risk individuals.

The researchers concluded that further studies should be done on the role of green tea in reducing breast cancer risk in young women.

Use in Breast Cancer Treatment

Given the potential for breast cancer prevention, it's natural to wonder if green tea could also slow down the growth of cancer cells in people who already have breast cancer.

So far, most studies have been done on breast cancer cells in the lab or in mice (meaning they cannot be applied to humans), but the results to date are encouraging.

To understand the growth of cancer, and how green tea may work, it's helpful to think of the different processes that must take place for cancer to grow and spread. In looking at these separate steps, researchers have found that:

• Chemicals in green tea appear to inhibit the growth of cancer cells in a lab. Several studies have found the division of breast cancer cells and increase in size of a tumor (albeit in a lab dish or in mice) was decreased by green tea components.
• Green tea was found to limit metastases to the lungs and liver, common places for breast cancer to spread, in rodents with breast cancer. Since most breast cancer deaths are from metastases (spread of breast cancer cells), this is very good news.
• Green tea may help with programmed cell death (apoptosis) of breast cancer cells. To understand this, it helps to understand that normal cells "commit" apoptosis when they become injured or old. Cancer cells seem to have found a way to avoid this process, essentially making them "immortal," so getting these abnormal cells to die off, as they should, is an important step.

However, researchers who conducted a 2019 study that looked at all tea consumption and its association with breast cancer found that green tea was not alone in its favorable association with progression-free survival. In fact, the only variety that was not linked to favorable outcomes was oolong (the next phase of Camellia Sinensis' development after green).

Adjuvant Therapy

In these studies, green tea was not used as a substitute for conventional treatment, but rather as an adjunct to the best current treatment approaches. Some researchers suggest that green tea may one day become part of a breast cancer treatment plan.

Of importance to many people being treated for breast cancer is the possible effect on long-term treatment—hormonal therapy—for breast cancer. The news on this account looks good. A few studies found that green tea acted together with the drugs tamoxifen and raloxifene in a positive way.

In other words, the combination of green tea and one of these medications worked better for inhibiting estrogen-positive breast cancer cells than either the medication or green tea alone.

Studies also suggest that green tea does not interfere with the function of aromatase inhibitors, another long-term breast cancer treatment option. That said, it also doesn't appear to help it. Thankfully, studies looking at both estrogen receptor-positive and estrogen receptor-negative breast cancer cells found some possible benefits from green tea.

Some vitamin or mineral supplements may interfere with treatment, and this is true with dietary additions as well. Talk with your healthcare provider about this to ensure that what you eat and take (green tea or otherwise) won't impact the effectiveness of your regimen.

Tips for Enjoying Green Tea

It has become easy to find green tea in the United States, thanks largely to well-publicized health benefits. When it comes to cancer benefits, though, there are a few guidelines to follow.

A few things to keep in mind:

• Be cautious about bottled green teas on store shelves. Many of them contain high amounts of sugar. Because excess sugar consumption can lead to obesity and obesity increases cancer risk, it's not a good idea in general to add sugary beverages to your diet.
• So-called herbal teas are not true teas, meaning they don't come from the Camellia sinensis plant. (They're more accurately called infusions or tisanes.) While some herbal infusions are made using medicinal plants, they do not have the same health effects as true teas.
• Be sure you brew green tea properly. It will make it taste better, but, more importantly, it'll preserve the EGCG so your body can absorb the maximum amount.
• Green tea does contain caffeine, so be on the lookout for potential side effects, such as heart palpitations and nervousness, and adjust your consumption as needed. Decaffeinated green teas are available, as well.

A Word From Verywell

It's important to remember that green tea (and other nutritional anti-cancer approaches) are no substitute for proven cancer treatments such as surgery, radiation, chemotherapy, and hormone therapy. Rather, it's something to consider talking to your doctor about.