High Blood Pressure and the Microbiome

When I write about the incredible incidence of so many chronic illnesses, I always feel a little like the grim reaper.  But what can I do?! Inflammatory diseases are on the rise in the industrialized world and so many are being related to the gut biome that I feel compelled to cover them!  This week on my Facebook page, for example, I shared a post about the cancer, multiple myeloma, and emerging evidence of a biome link.  That’s a new one for me – and there seems to be new ones all the time.  On that note, today’s topic is high blood pressure (BP) which is found at insanely high incidence in  the USA.  According to the CDC, more than 47% of men and 43% of women are currently suffering from this.[i]  Closing in on half our friggin’ population?!

With these statistics in mind: as I slowly make my way through my ever-growing stack of papers to read, I came across one from July that I thought I’d share today.  As these scientists write in their opening sentence:  “Hypertension is one of the most powerful risk factors for cardiovascular events, including stroke and myocardial infarction.  Around one quarter of the world’s population is considered hypertensive and it is responsible for 41% of the cardiovascular disease related deaths.”  Unbelievable.

The authors point out that, “…an imbalance in the gut microbiota composition relative to healthy state, termed dysbiosis, has been associated with hypertension,” but the mechanisms of action are as yet unknown.  So far, there are a fair number of studies that indicate “…a direct association between hypertension and gut microbiota in both animals and humans.”  The article describes multiple animal studies, as well as findings in humans.  Highlights:

1. In a case study, a combination of antibiotics reduced the blood pressure in a resistant hypertension patient from 160/90 to 130/60.
2. In 9 patients with resistant hypertension, the antibiotic, minocycline, progressively reduced BP over a 36 week period of time. However, there is anun issue with assuming that the mechanism of action is the direct effect of antibiotics on the gut flora:  antibiotics are often both anti-inflammatory and immunomodulatory, so how these antibiotics accomplished the BP reduction is actually not known.  Thus, more research was needed…see below!
3. In animals and people, hypertension is associated with a reduction of bacterial diversity; lower levels of Bacterioidetes and higher levels of Firmicutes bacteria; higher levels of lactate-producing bacteria;  and a reduction in bacteria that produce the short-chain fatty acids acetate and butyrate.
4. In fact, hypertension has been significantly negatively associated with an abundance of butyrate-producing bacteria; specifically, the butyrate-producing genus Odoribacter is inversely correlated to high systolic (top number) BP.  (That is, the lower the level of the bacteria, the higher the BP.)
5. When the microbiome of rats with hypertension was transplanted into normal rats, it induced a significant rise in BP. Such experiments have been repeated many times in various iterations.  Gut bacteria from hypertensive humans, transplanted into germ-free mice, also caused a significant rise in BP in the animals.
6. The relationship between a dysfunctional sympathetic-gut-immune system triangle is now known to be a part of the hypertensive picture. Increased sympathetic activity to the gut leads to increased gut permeability (leaky gut), which in turn, leads to immune activation and inflammation.
7. One research group has linked hypothalamic neuroinflammation and increased sympathetic nervous system involvement with changes in the gut and microbiome, associated with a particular type of hypertension, Ang-II. I didn’t know what this meant either, so I looked it up![ii]  Angiotensin is the name for 4 different hormones (labeled I-IV) which play important roles in body health and blood pressure.  Angiotensin-II is the one that plays the big role in BP: it causes blood vessels to constrict.  It can also trigger thirst and the desire for salt. In a rodent study, giving the medication, losartan, which is an angiotensin antagonist, not only improved gut barrier integrity, but is also improved the quality of the bacterial microbiome.
8. “A growing body of evidence supports the role of the immune system and exaggerated inflammatory responses in the development of hypertension.” Well, that should come as a surprise to exactly no one.  Regulatory t-cells, which modulate inflammation, offer protection against increase BP.

To sum up:  “Collectively, all data suggest an association between gut microbial dysbiosis and hypertension…Gut microbiota is now recognized as a target for dietary interventions with prebiotics or probiotics to reduce BP…”  However, we are far from knowing exactly how to do this manipulation yet – we need way more research.  In the meantime, you have to believe that it is no coincidence that those things that are known to reduce BP (i.e. a good diet, exercise, stress reduction, weight loss, etc.) are also known to improve the quality of the microbiome.

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[i] https://www.cdc.gov/bloodpressure/facts.htm

[ii] https://www.hormone.org/your-health-and-hormones/glands-and-hormones-a-to-z/hormones/angiotensin