The Blood Brain Barrier (BBB) is effectively our brain’s own ‘policing system’, a physical barrier that separates our blood circulation from the central nervous system. The deterioration of this highly intelligent barrier has been linked to many neurological conditions, one of which is Alzheimer’s, the most common form of Dementia (1). Up until recent years the complexity of the BBB was not fully understood, researchers believed that any molecule small enough could penetrate it. However, new technology that allows scientists to look into the brain to a depth of a millimetre whilst the brain is still functioning, has revealed just how complex this layer of cell junctions actually is (2)

The homeostatic function of the BBB is essentially to protect the brain from exposure to molecules such as pathogens, viruses and parasites as well as many other compounds, which can be toxic to the brain. This tightly regulated system is managed by endothelial cells which are closely-fitted together and a myriad of molecular passageways embedded in the membrane of the cells (3) These intelligent structures work by actively pushing molecules across that the brain requires such as nutrients and blocking others that are harmful. It can be likened to having our very own border control, filtering out what we need and don’t need.

Neurological conditions such Alzheimer’s and Parkinson’s have been linked to a leaky blood brain barrier, where the tight junctions become lose, therefore allowing through molecules which would otherwise not have been able to (4). Until recent years, dysfunction of the central nervous system and neurodegenerative disease in particular, has excluded the impact of factors outside of the central nervous system. Peripheral factors such as toxins and the adaptive immune system have been shown to play a significant role in the pathogenesis and the development of neurodegenerative disease (5).

A recently conducted study has revealed how a key influencing factor in the permeability of the BBB may well be our gut bacteria. Tests carried out on germ-free mice with no normal gut flora displayed increased blood brain barrier permeability compared to those with normal gut flora. Furthermore, the results demonstrated a reduced expression of the cell junction proteins, which regulate the function of the barrier in endothelial cells (6). This led to a reduced development of nerve cells in the hippocampus, the area of our brain which is known for where we process memory and emotions (7). Studies like these further strengthen the theory that the gut and the brain work in tandem and are in constant communication with each other. Although it is important to note that these are animal studies and more funding should be allocated to research using human subjects, something that Food for the Brain continues to campaign for in relation to dementia prevention.

Our gut bacteria are responsible for the digestion and assimilation of our food, the modulation of our immune system, the synthesis of nutrients and gut motility, as well as maintaining the health of the cells in the lining of our gut (8) Medications such as antibiotics, antacids and common painkillers have been known to significantly impact the diversity and number of bacteria in a negative way. A study undertaken in Norway tested 1135 participants to measure how environmental factors such as diet and medication influence bacteria. Results revealed that our bacteria can be affected by up to a year after taking antibiotics (9).

There are many things we can do to positively impact the ecology of our gut. Eating a balanced diet with plenty of vegetables, whole grains, fermented foods such as sauerkraut, good quality sources of fat such as omega 3 found in oily fish, as well as staying away from refined sugars and trans fatty acids, can help maintain the ecology of our gut. If you would like more information about eating a balanced diet to support cognitive health, we have created our very own e-guide as part of our ‘Take Positive Action’ campaign, promoting how diet and lifestyle factors can support better cognitive health and reduce the risk of Alzheimer’s and dementia. For a suggested donation of £5, you can receive a copy of the e-guide and will be helping us to reach more people with information on the importance of nutrition in mental health. Please follow the link here to donate and receive your copy, or contact us at

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