The brain and the gut are linked by the gut brain axis, the most direct link between the intestine and brain being the vagus nerve. It has parasympathetic (unconscious) control of basic gut functioning.
This is thought to be due to the microbiome we all have in our gut, which is made up of approximately 1014 microorganisms which can weigh up to 5 pounds.
The gut is especially important as it has it’s own nervous system (enteric nervous system). Therefore it is also known as the gut brain as it can control certain processes independently.
The gut brain axis is bidirectional, linking cognitive areas of the brain to intestinal functioning. The brain affects the guts functioning and the gut the brain.
The creation of the microbiome
The composition of the guts microbiome is established by the age of three after this it mainly stays stable throughout life. Its composition is determined by a child’s genes and environment
Six factors which influence the gut microbiome:
- Prenatal and perinatal exposure to maternal microbes
- Route of delivery (vaginal vs. cesarean)
- Infant diet (breast vs. formula feeding, onset of solid food)
- Environmental (familial transmission, exposure to environmental microbiota)
- Antibiotic use
Autism and Gut Bacteria
Autism is a neuro-development disorder that effects a person’s social interactions, ability to understand other people and can cause repetitive behaviours. In extreme cases people cannot communicate with others and it can be a very challenging condition for the individual and their family.
Although it’s known that autism is caused by neuro-development abnormalities, their cause is still unknown. Researchers have hypothesised that gut bacteria abnormalities could be a contributing factor.
Studies have shown children with ASD (autism spectrum disorder) have more stomach problems than non autistic children – 70% to 28%. In addition the symptoms have been found to be strongly correlated to the severity of autism . Ammonia and free amino acids were found in increased levels in urine in children with autism , both products of microbial fermentation.
Alzheimer’s and Parkinson’s
In neuro-degenerative diseases (diseases of the brain due to ageing) have now been linked to chronic pro-inflammatory immune (CPI) disease.
As you age the blood brain barrier becomes more permeable, this means that harmful toxins can pass easier from the blood to the brain .
CPI can cause the intestine wall to become more permeable allowing metabolic products into the bloodstream. This blood then travels to the brain, with an already compromised BBB the metabolites are going into the brain and can cause potential damage.
For example amyloid a product of certain bacteria if it gets into the brain can cause plaque build up between neurons. This plaque is thought to be one of the causes of Alzheimer’s as they disrupt the messages between the neurons.
Depression and Anxiety
300 million individuals across the globe suffer from depression. Individuals with this disease commonly suffer with appetite issues, over or under eating. The cause of this is unknown however some researchers hypothesise that this may be a sign of abnormal gut activity rather than an neurological abnormality.
In patients with major depressive disorder the composition of gut bacteria has been found to be significantly different to control groups. The number of different species being a lot lower than in healthy controls.
Depression runs through families and some scientists believe this may be due to the vaginal microbacteria babies acquire during birth. Which will effect their composition for the rest of their lives.
Looking to the Future…..
It seems impossible that conditions of the brain may stem from the composition of bacteria in the intestines. But hopefully from this research there will be a new era of drug treatment, which may save lives!!!