Some Early-Stage, But Promising, Science About the Microbiome and Cancer
Yesterday morning, I posted a story on my Biome Buzz’ Facebook page about 2 new studies that independently showed that there is a distinctive microbiome composition associated with colorectal cancer.[i] One study “…identified a set of 29 species indicative of colorectal cancer across 7 countries,” while the other showed “…higher gut microbiome richness” than controls, which ordinarily sounds like it should be a good thing but in this case, that richness came from bacteria that are native to the mouth that had moved to the colon, where they are not meant to be. This led to altered glucose metabolism in the large intestine, as well as the “putrification” of amino acids, etc.
I read that article with great interest as I was intending to start writing this post about a recent summary of what we currently know about using probiotics in treating and preventing cancer – and you all know I love coincidences![ii]
Upon reading this new article, the first thing that struck me was how long ago research into the connection of cancer to the gut bacteria began. Back in 1980, two researchers (Goldin and Gorbach[iii]) first demonstrated an, “…association between a diet enriched with Lactobacillus and a reduced incidence of colon cancer (40% vs. 77% in controls)”! That’s almost 30 years ago! And so very little progress, really, has been made since then. Of course though, thankfully, there has been at least some.
So a few highlights:
- The authors enumerate several potential mechanisms of action as to how probiotic bacteria prevent cancer. Of course, “A specific mechanism associated with anti-tumor properties of probiotics remains unclear.”
- Probiotics can help prevent excessive bile acids (which is carcinogenic) from adversely affecting the lining of the colon: “…probiotic bacteria such as L. acidophilus and B. bifidum have been demonstrated to be a promising tool in cancer prevention.”
- Putrification (pathogenic) bacteria, like E. coli and Clostridium perfringens, both of which are naturally found in the human gut, create carcinogenic compounds using certain enzymes. In the late 1970s, the two researchers I mentioned above (Goldin and Gorbach), showed – in rats – that eating fermented milk products (ie. yogurt or kefir) had a beneficial effect on the amount of L. acidophilus in the rodents’ intestines which “…subsequently resulted in a reduction of putrefactive bacteria and decrease in the level of harmful enzymes.” This has been confirmed in more recent research.
- Lactobacillus and Bifidobacillus bind and degrade potential carcinogens. For example, these strains alleviate the effect of eating carcinogenic compounds found in unhealthy foods, like fried meats.
- Many of the metabolites produced by the probiotic bacteria themselves play “…an essential role in maintaining homeostasis and suppressing carcinogens.” The authors specifically talk about short chain fatty acids (SCFAs), which you’ve heard me talk about many, many times on this blog. (For example, here and here.) SCFAs beneficially affect the immune system, cell proliferation and cell death (which, in the case of tumor cells, you can imagine is pretty critical!), as well as help maintain “epithelial integrity” (ie. leaky gut).
- At this point, the authors actually make a really interesting point: lactic acid producing bacteria are not directly involved in SCFA production, but they modulate the gut microbiota which, in turn affects the production of SCFAs. That is, Lactobacilli and Bifidobacteria, are indirectly crucial in SCFA production.
- “Colorectal cancer is strongly correlated with decreased levels of SCFA and SCFA-producing bacteria dysbiosis,” as I mentioned in the opening paragraph of this post. In mice, boosting levels of bacteria which produce the SCFA, butyrate, for example, inhibits the progression of tumor development. So…eat your fiber (said Judy, for the millionth time…like here!) Or, as these authors write, “…the prebiotic activity of fiber-enriched diet…is a promising strategy to prevent CRC [colorectal cancer].”
- Probiotic bacteria also have the ability to increase and decrease inflammatory cytokines (chemical messengers) in the body, as well as modulating the production of prostaglandins, which are immune compounds which suppress cancer formation. They can also activate immune cells called phagocytes, which directly eliminate early-stage cancers.
- Probiotic bacteria can suppress gastric cancers related to H.pylori infections, as well as clear the virus, HPV, which is associated with cervical cancer. A study on humans showed enhanced clearing of HPV with 6 months of consumption of probiotics.
- A 2012 meta-analysis of 19 different human cohort studies showed an “association between consumption of dairy products (except cheese) and a decreased colorectal cancer risk.” A second study confirmed these findings. (However, high fat dairy does increase bile acid levels in the colon, which – as noted early – may be carcinogenic.) Also of note: a huge cohort study, on 45,241 subjects, “proved a significant association between single probiotic-rich product intake (yogurt) and decrease colon cancer risk.”
- The paper takes a brief look at the future, in terms of using probiotics to treat cancer. For example, scientists have used probiotic bacteria to modulate the immune response and have even been able to entirely inhibit tumor development. Others are working on using probiotics as “vaccines,” manipulating the immune system to fight off various carcinogenic pathogens, like HPV (the virus that can cause cervical cancer). And still others are using probiotics to more effectively deliver medicines to where they are most needed.
Unfortunately, as I said earlier, all this research – as promising as it is – is still pretty early stage, as most studies have been done in animals. On the bright side, I hope with all my heart (considering how many people I already know who have had to fight (and all-too-often succumbed to) cancer: “…evidence from the latest studies points towards the idea of possible implementation of probiotics in cutting-edge cancer therapy.”
[ii] Gorska, A, Przystupski, D, Niemczura, MJ, Kulbacka, J. Probiotic bacteria: a promising tool in cancer prevention and therapy. Current Microbiology. https://doi.org/10.1007/s00284-019-01679-8
[iii] Goldin BR, Gorbach SL (1980) Effect of Lactobacillus acidophilus dietary supplements on 1,2-dimethylhydrazine dihydrochloride-induced intestinal cancer in rats. J Natl Cancer Inst64:263–265.