The blood–brain barrier (BBB) is a highly selective permeability barrier that separates the circulating blood from the brain extracellular fluid (BECF) in the central nervous system (CNS). The blood–brain barrier is formed by capillary endothelial cells, which are connected by tight junctions with an extremely high electrical resistivity.
The BBB is distinct from the quite similar blood–cerebrospinal-fluid barrier, which is a function of the choroidal cells of the choroid plexus, and from the blood–retinal barrier, which can be considered a part of the whole realm of such barriers.
The BBB has several important functions:
- Protects the brain from “foreign substances” in the blood that may injure the brain
- Protects the brain from hormones and neurotransmitters in the rest of the body
- Maintains a constant environment for the brain
The general properties of the BBB include:
- Large molecules do not pass through the BBB easily
- Low lipid (fat) soluble molecules do not penetrate into the brain. However, lipid soluble molecules, such as barbituate drugs, rapidly cross through into the brain
- Molecules that have a high electrical charge are slowed
The BBB can be broken down (permeated) by:
- Hypertension (high blood pressure): high blood pressure opens the BBB.
- Hyperosmolitity: a high concentration of a substance in the blood can open the BBB.
- Microwaves: exposure to microwaves can open the BBB.
- Radiation: exposure to radiation can open the BBB.
- Infection: exposure to infectious agents can open the BBB.
- Trauma, Ischemia, Inflammation, Pressure: injury to the brain can open the BBB.
Through extensive study, scientists have found that compounds that are very small and/or fat-soluble, including antidepressants, anti-anxiety medications, alcohol, cocaine, and many hormones are able to slip through the endothelial cells that make up the blood-brain barrier without much effort. In contrast, larger molecules, such as glucose or insulin, must be ferried across by proteins. These transporter proteins, located in the brain’s blood vessel walls, selectively snag and pull the desired molecules from the blood into the brain.
When the blood-brain barrier breaks down, as is the case in some brain cancers and brain infections or when tiny ruptures to blood vessels occur, some substances that are normally kept out of the brain gain entry and cause problems for the brain.
Mercury penetrates the blood-brain barrier around the brain, and as little as one part per million can impair this barrier, permitting entry of substances in the blood that would otherwise be excluded. 1
There are a number of natural substances that can be consumed to maintain the integrity of and enhance the blood-brain barrier. These natural substances are listed in the Table below:
Natural Substances that Maintain the Integrity of and Enhance the Blood-Brain Barrier
Category Natural Substance References
Foods Bilberry 1
Herbs Ginko Biloba 2
Hormones Progesterone 3
Polyphenols Anthocyanins (Plants rich in anthocyanins are Vaccinium species, such as blueberry, cranberry, and bilberry; Rubus berries, including black raspberry, red raspberry, and blackberry; blackcurrant, cherry, eggplant peel, black rice, Concord grape, muscadine grape, red cabbage, and violet petals. Red-fleshed peaches and apples contain anthocyanins.) 4 5
Vitamins Vitamin B1 (Vitamin B1 deficiency can lead to break down of BBB) 7 8
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