leaky gut leaky brain

A Depleted Gut Compromises the Blood Brain Barrier

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A healthy blood-brain barrier is necessary for keeping unwanted molecules and cells from entering into the brain from the bloodstream. Without a healthy blood-brain barrier, pathogens can pass from the bloodstream into the brain, causing illness and even death. The blood-brain barrier also maintains central nervous system (CNS) homeostasis and ensures an optimal environment for neuronal function and growth.

For many years it was thought, and taught, that the blood-brain barrier was impenetrable. However, a 2014 study found that gut microbiota affect blood-brain barrier permeability, and that a depleted gut microbiome leads to increased blood-brain barrier permeability in mice. Since we live in a world full of antibiotics, and many people have compromised gut microbiota, the findings of this study are potentially consequential for humans.

Gut Bacteria and the Blood Brain Barrier

In a groundbreaking study, “The gut microbiota influences blood-brain barrier permeability in mice,” published in Science Translational Medicine, researchers measured blood brain barrier (BBB) permeability of mice pups born to mothers who were germ-free and compared them to mice pups born to mothers who had a normal, pathogen-free, gut biome makeup. What they found was striking: “germ-free mice, beginning with intrauterine life, displayed increased BBB permeability compared to pathogen-free mice after birth and during adulthood.” The BBBs were more permeable for mice born to mothers who didn’t have normal gut microbes, and they remained so throughout the pup’s lives, unless they received a fecal transplant. The mice who received a fecal transplant of normal gut bacteria had less BBB permeability. This means that the state or composition of intestinal bacteria, the gut microbiota, affects brain function in a some pretty significant ways. Specifically, gut bacteria determines whether the blood brain barrier is tightly controlled and capable of repelling pathogens and toxicants or permeable to outside scourges.

The researchers “demonstrated that lack of gut microbiota is associated with increased BBB permeability and altered expression of tight junction proteins. Fecal transfer from mice with pathogen-free gut flora into germ-free mice or treatment of germ-free mice with bacteria that produce short chain fatty acids (SCFA) decreased the permeability of the BBB.”

For pregnant women, this means that mom’s intestinal health contributes to the mechanisms that close the BBB before birth. It also suggests that, at least through early development, gut health continues to impact how tightly the junctions in the BBB close.

Gut Health Linked to Brain Health: Implications for Pregnancy and Beyond

This research raises interesting questions about how the human microbiota influence human brain health. Specifically, how exposure to antibiotics, and other products alter gut bacteria and subsequently influence brain function in the developing fetus and across the lifespan. In the-scientist.com, Stephen Collins, Director of the Farncombe Family Digestive Health Research Institute at McMaster University in Ontario, noted that,

For example, antibiotic usage during pregnancy theoretically—if these results can be extrapolated to humans—could actually have some impact on brain development.

The development and final closure of the blood-brain barrier isn’t quite finished at birth. So, again, anything that interferes with intestinal bacteria . . . after the child has been born could also prevent the proper closure of that barrier and therefore the proper development of the brain.

Some things that may affect the maternal microbiome include antibiotic use, exposure to antibacterial household and beauty products, exposure to glyphosate, and more. It is assumed that most antibiotics are safe for use during pregnancy–they are prescribed to pregnant women regularly. While the dangers of antibacterial soap and other products are being realized, their particular danger to pregnant women and developing fetuses is not recognized.

Some research suggests that maternal antibiotic use is responsible for the rise in Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). PANDAS occurs when a streptococcus (strep) infection gets into the brain and an autoimmune reaction occurs. In people with an intact BBB, strep bacteria stays out of the brain. However, a permeable blood brain barrier may allow strep bacteria to infect the brain, causing PANDAS.

Another potential implication of the study is that antibiotic use that results in a permeable blood brain barrier increases the chances of a child being injured by vaccines. Dr. Stephanie Seneff hypothesizes that vaccine-injuries occur when there is gut microbiota depletion (she asserts that the gut microbiota damage is due to glyphosate exposure), and this gut microbiota depletion increases the risks of vaccine adjuvants like aluminum getting into the brain and causing damage. The BBB permeability caused by gut microbiota depletion shown in “The gut microbiota influences blood-brain barrier permeability in mice” supports Dr. Seneff’s assertions. (Additionally, the microbiome is intertwined with the immune system, as shown by the article, “Immune modulation of the brain-gut-microbe axis.”)

This research provides additional evidence of the links between gut microbiota depletion and many diseases of modernity, especially neurological diseases that are presenting in children. Others, however, see this study as an opportunity for drug manufactures to better reach the brain with pharmaceuticals. On the Karolinska Institutet web site, Professor Sven Pettersson, the principal investigator at the Department of Microbiology, Tumor and Cell Biology, stated,

This knowledge may be used to develop new ways for opening the blood-brain-barrier to increase the efficacy of the brain cancer drugs and for the design of treatment regimes that strengthens the integrity of the blood-brain barrier.


The connections between the human gut biome and the brain are becoming increasingly apparent, and the damage that we have done to our gut biome through excess use of antibiotics, antibacterial soap, glyphosate, and more, is likely to be more consequential than anyone assumed a decade ago. If antibacterial products are diminishing human blood-brain barrier strength, that is just one more reason to stop going down the path of bacterial destruction in order to fight disease. When we indiscriminately destroy bacteria we diminish our strength as well. It’s time that the interconnectedness of our gut and overall health (including, maybe especially, our brain health) is recognized.

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Image was created using Canva AI.

This article was published originally on November 2, 2016. 

Lisa Bloomquist was "Floxed" on her 32nd birthday by Cipro, a fluoroquinolone antibiotic. After 2 years of battling the mysterious health ailments that come with an adverse reaction to a fluoroquinolone, she has fought her way back to health. Lisa is now fighting for recognition of the harm that these drugs can cause and hoping to help those who are suffering from them through their fluoroquinolone induced illness to find recovery. Her web site, highlighting stories of hope and recovery, is www.floxiehope.com. After a while of studying how fluoroquinolones damage mitochondria, she noted that mitochondria were being systematically ignored when forming disease models. She started www.mitomadness.com to bring attention to the role that mitochondria play in health and disease.

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