Tea compounds possess properties that may help suppress undesirable microbes
by Craig Weatherby
Most of the research into the health benefits of tea focuses on the antioxidant and metabolism-boosting activity of its polyphenol compounds: specifically, catechin-class flavanols like the ones also concentrated in raw cocoa and extra-dark chocolate.
But, as we reported last week, research by scientists from the US Department of Agriculture and South Korea discovered that the anti-cancer power of tea may not depend entirely on its polyphenol content or their antioxidant effects (See “Tea's Anti-Cancer Powers Affirmed and Expanded”).
Now, we may have some clues why. The findings of two studies—from teams at the National University of Singapore and Korea University in Seoul—indicate that polyphenols and special carbohydrates in tea do two very good things:
- Suppress the growth of pathogenic (disease-promoting) bacteria in the gut.
- Reduce the ability of pathogenic bacteria to adhere to the lining of the intestines.
Let's delve into this a little deeper.
The overlooked importance of intestinal bacteria to human health
The title of a recent literature review from researchers at the National University of Ireland—“The gut flora as a forgotten organ”—says it all (O'Hara AM, Shanahan F 2006).
The accuracy of their paper's title stems from the fact that the so-called “mucosal immune system” in the lining of the gastrointestinal tract is one of the largest components of the body's immune system.
If you think about it, the importance of the mucosal immune system seems unsurprising, since much of what enters our body gets in through our mouths.
And the importance of the tea findings we're reporting here rests on the fact that the billions of bacteria that reside in our intestines—our so-called “microflora”—represent a key influence on the mucosal immune system.
As the Irish authors wrote, “The intestinal microflora is a positive health asset that crucially influences the normal structural and functional development of the mucosal immune system.… The flora has a collective metabolic activity equal to a virtual organ within an organ… It follows that manipulation of the flora to enhance the beneficial components represents a promising therapeutic strategy” (O'Hara AM, Shanahan F 2006).
Their comments are echoed by ones in a review article from researchers in the Mucosal Immunology Laboratory of Massachusetts General Hospital for Children, a teaching hospital of Harvard Medical School:
“…changed lifestyles and the increased use of antibiotics are significant factors that affect the preservation of a healthy intestinal microflora. The concept of probiotics is to restore and maintain a microflora advantageous to the human body” (Broekaert IJ, Walker WA 2006).
Before we go further, we need to define four key terms:
- Probiotic bacteria such as Lactobacillus acidophilus create a chemical environment unfriendly to pathogenic (disease) bacteria in the gut.
- Prebiotic means anything—such as certain bacteria and carbohydrate compounds—that stimulates and support the growth of probiotic bacteria. The most commonly used supplemental prebiotic agents are inulin [sic] and oligosaccharides. (The results of the research we're reviewing today appear to add tea to this list of prebiotic agents.)
- Commensal bacteria are the beneficial microbes normally found in human intestines, which produce essential nutrients as a byproduct of their own metabolism and help us digest our food and extract nutrients from it.
- Pathogenic bacteria are microbes that can cause disease.
Singapore study finds tea polyphenols friendly to gut health
A team at the National University of Singapore tested the effects of 31 different polyphenols from Yunnan Chinese tea on the growth of 28 different bacteria, including pathogenic, commensal (normal/friendly), and probiotic microbes found in the intestine.
The microbes the Singaporeans exposed to tea polyphenols included a half-dozen serious villains: E. coli, Salmonella enterica, Bacteroides spp., Clostridium perfringens, Clostridium difficile and Listeria monocytogenes.
They also exposed two normal (commensal) gut bacteria—Clostridium spp. and Bifidobacterium spp.—and a probiotic bacteria called Lactobacillus acidophilus to tea polyphenols.
(L. acidophilus and Bifidobacterium spp. are often added to natural brands of yogurt, and are sold as supplements.)
The tea polyphenols tested—and/or their digestive metabolites (breakdown products)—inhibited strongly the growth of all six pathogenic microbes, strongly.
In contrast, the tea compounds had little effect on the growth of friendly commensal and probiotic bacteria such as L. acidophilus and Bifidobacterium spp.
As the researchers said, “This indicates that tea phenolics exert significant effects on the intestinal environment by modulation of the intestinal bacterial population, probably by acting as metabolic prebiotics... The bioactivity of different phenolics may play an important role in the maintenance of gastrointestinal health” (Lee HC et al 2006).
Koreans identify other beneficial compounds in tea
Unlike the Singapore findings, the results of a study from South Korea went unreported in the media, but seem potentially significant, in terms of illuminating the various ways in which tea may help prevent overgrowth of "bad" intestinal bacteria, some of which can promote cancer (Lee JH et al 2006).
You've probably heard that cranberry juice can help prevent and treat urinary tract infections.
Cranberry juice aids women in this way because compounds in cranberries prevent the bacteria responsible for urinary tract infections from adhering to tissues in the affected area.
And the new findings suggest that tea may offer similar “anti-adhesive” benefits.
The Korean team exposed various bacteria to a pectin-like tea compound that belongs to the category of chemicals known as polysaccharides, which are long chains of sugar molecules.
Certain polysaccharides exert anti-microbial or immune-boosting effects. The major anti-cancer, anti-viral, immune-modulating compounds in medicinal mushrooms (e.g., shiitake, maitake) are polysaccharides, as are some of the beneficial chemicals in the immune-modulating herb Echinacea.
Their results indicate that a tea polysaccharide called CS-F2 may offer cranberry-like anti-adhesive effects against pathogenic bacteria in the human gut:
- Helicobacter pylori—the cause of most ulcers, which promotes gut cancers
- Propionibacterium acnes—the microbe that promotes acne
- Staphylococcus aureus, which is the bane of hospitals worldwide
While the polysaccharide from tea did not inhibit growth of two other major pathogens—E. coli and Staphylococcus epidermidis—neither did it exert any ill effects on friendly probiotic/commensal bacteria such as L. acidophilus and Bifidobacterium spp.
As the Koreans reported, “Our results suggest that CS-F2, which is a pectin-type polysaccharide… may exert a selective anti-adhesive effect against certain pathogenic bacteria, while exerting no effects against beneficial and commensal bacteria” (Lee JH et al 2006).
(Note: It is not clear how much of this polysaccharide occurs in a typical cup of tea, as opposed to tea leaves)
The recent findings from East Asia will come as welcome news to dedicated tea drinkers, and should prompt others to become devotees of the beneficial brew, whose list of positive health attributes just continues to grow.
- Broekaert IJ, Walker WA. Probiotics and chronic disease. J Clin Gastroenterol. 2006 Mar;40(3):270-4. Review.
- Broekaert IJ, Walker WA. Probiotics as flourishing benefactors for the human body. Gastroenterol Nurs. 2006 Jan-Feb;29(1):26-34. Review.
- Lee HC, Jenner AM, Low CS, Lee YK. Effect of tea phenolics and their aromatic fecal bacterial metabolites on intestinal microbiota. Res Microbiol. 2006 Nov;157(9):876-84. Epub 2006 Aug 18.
- Lee JH, Shim JS, Lee JS, Kim JK, Yang IS, Chung MS, Kim KH. Inhibition of pathogenic bacterial adhesion by acidic polysaccharide from green tea (Camellia sinensis). J Agric Food Chem. 2006 Nov 15;54(23):8717-23.
- No authors listed. Green tea. Altern Med Rev. 2000 Aug;5(4):372-5.
- O'Hara AM, Shanahan F. The gut flora as a forgotten organ. EMBO Rep. 2006 Jul;7(7):688-93. Review.