Colorectal cancers are the third most common cancer that affects both men and women, and the second leading cause of cancer-related deaths in the US.
The numbers of deaths have been declining in recent years, thanks to early screenings and colonoscopies.
More can be done to help prevent the 50,000 deaths attributable to colorectal cancer yearly.
One of the most promising discoveries is that green tea and its most active polyphenol constituent, epigallocatechin gallate (EGCG) has potent actions against colorectal cancer.
In the past year, new research findings have been published on green tea’s effects on colorectal cancer.
Together, these studies tell a compelling story about green tea’s potential cancer-preventive properties.
Green Tea vs. Colorectal Cancer
Researchers decided to pool data from dozens of studies that evaluate green-tea consumption and the risk for colorectal cancers.
Published in 2017, this ambitious study combined 29 separate epidemiological studies, with a total of more than 1.6 million individuals.
This meta-analysis had two main findings:
- First, it showed that green tea consumption is associated with protection against colorectal cancers, demonstrating a 7% overall reduction in risk.
- The second finding showed that among female green-tea drinkers, for every cup per day of tea consumed, colorectal cancer risk was reduced by 32%. This established a dose-response relationship—meaning the more you drink, the more protection you get.
This large study helps clarify green tea’s association with colorectal cancer protection in humans.
COLORECTAL CANCER BY THE NUMBERS
The most recent year that comprehensive statistics on colorectal cancers are available is 2014, when:
- Nearly 140,000 people were diagnosed with colorectal cancer, including:
- 73,396 men
- 66,596 women
- 51,651 Americans died of colorectal cancer, including:
- 27,134 men and
- 24,517 women
The good news is that rates of both colorectal cancer incidence and mortality have been gradually falling, but only by around 3% per year overall. This is largely attributable to increasing rates of screenings and colonoscopies.
Animal Studies Show Cancer Reduction
In an effort to better understand the impact of green tea on reducing the risk of colon cancer, researchers designed two studies with mice. Both sought to determine whether green tea reduced the presence of tumors in the colon.
The scientists conducting the first study had already shown that a green tea polyphenol extract significantly inhibited the formation of precancerous lesions in the colon.
Next, they wanted to assess green-tea extract’s impact on colorectal tumors themselves. To determine this, they treated rats with a chemical that induces colorectal cancer. The rats were also fed a high-fat diet, which is known to promote colorectal cancers.
Half the animals were supplemented with green-tea polyphenol extracts for 34 weeks, while the other half served as unsupplemented controls.
The study showed that, while most of the control animals developed colorectal cancers, significantly fewer of the supplemented rats did.
And of the supplemented animals that did develop tumors,
- there were 55% fewer tumors in each animal,
- the tumors were 45% smaller,
- and the tumors that did develop were more likely to be benign than malignant.
In addition to these direct impacts on tumors, the green-tea polyphenol extract had numerous other anti-cancer benefits.
For example, the supplemented animals had significantly lower levels of pro-inflammatory signaling molecules, lower expression of a tumor-promoting gene regulator called beta-catenin, and higher levels of tumor-cell death.
This study establishes that green tea polyphenols prevent inflammation-promoted colorectal cancers in a standard animal model.
Diminishing the Diet/Cancer Connection
The second animal study demonstrated a property of green-tea extract that is particularly important for today’s American population because it diminishes the impact that poor diet has on cancer.
Once again, the mice in this study were given a cancer-inducing chemical and then treated with a green-tea extract. This study found that green-tea extract reduced the occurrence of precancerous lesions.
And it was found to be even more effective in the group of mice fed a typical western diet high in fat and simple sugars. It also prevented weight gain and fasting glucose elevations only in that “poor diet” group. This was a key finding because these kinds of poor dietary choices are linked to increased cancer risk through increased insulin production and chronic inflammation.
So green-tea extracts appear capable of helping to overcome the harmful impact of poor dietary habits on the promotion of colorectal cancers—truly encouraging news.
Study Affirms Green Tea’s Colorectal Cancer Prevention
A new study not only validates the findings from epidemiological and animal studies, it also provides insight into how green tea protects against colorectal cancers.
First, in a basic lab study, researchers showed that the green tea polyphenol EGCG suppressed the activity of deadly colorectal cancer stem cells.
Like all stem cells, cancer stem cells are extremely robust. And because they divide infrequently, they are relatively resistant to chemo- and radiation therapies. Cancer stem cells are widely held to be responsible for the recurrence of treated cancers, functioning in essence as malignant “seeds” that can restart the malignant process even after the bulk of a tumor has been destroyed.
The way EGCG suppressed cancer stem cells was by downregulating a fundamental signaling pathway called Wnt/beta-catenin. This pathway is crucial in controlling the development of stem cells into functioning cells in tissues. Abnormal activation of the Wnt/beta-catenin pathway is a potent cancer promoter.
This pathway is already a target for pharmaceutical drug developers. Now, the authors of this study suggest that EGCG’s ability to suppress this signaling pathway could make it a promising agent for colorectal cancer intervention.
Follow the Logic
It’s nearly impossible to perform a human study demonstrating direct reduction in cancer occurrence because it would be unethical to expose human subjects to cancer-inducing chemicals. But scientists often use logic chains to draw strong conclusions about the likelihood that a substance—in this case, green tea—will have similar protective effects in humans as demonstrated in animal studies.
The logic here is powerful:
1. People who drink larger amounts of green tea have lower rates of cancer than those who drink less.
2. Animals that are given green tea and then exposed to cancer-causing chemicals develop fewer and smaller cancers when treated with green-tea extracts.
3. Those green tea-treated animals demonstrate significant reductions in known tumor-promoting pathways and signaling molecules that occur in humans as well.
4. Humans supplemented with green tea extracts demonstrate similar changes in the identical pathways, indicating a reduction in colorectal cancer risk produced by green tea.