Gamma-aminobutyric acid (GABA) is an amino acid that functions as an inhibitory neurotransmitter. It serves one-third of brain neurons and is involved in depression and mania.
Although there are some dietary supplement and food sources for GABA (cruciferous vegetables, spinach, tomatoes, beans, and rice), the primary source may be endogenous prodution.
Nervous tissue, the gut microbiome, the liver, pancreas, and endothelial cells are important sources for production. Endogenous GABA is produced by the decarboxylation of the excitatory neurotransmitter glutamic acid. It can also be produced from the diamine putrescine using diamine oxidase (DAO).
Also, the gut microbiome is capable of synthesizing various hormones and neurotransmitters. For example, Lactobacillus and Bifidobacterium species can produce GABA. In general, plasma GABA may reflect brain GABA activity, however urine GABA levels are felt not to correlate with CNS levels.
Decreased protein intake, GI maldigestion, and malabsorption can contribute to lower levels. Also, since GABA can be made endogenously from glutamic acid and other pathways, low glutamic acid levels, issues with enzymes like DAO, or an altered microbiome should also be considered. Reduced GABA levels are known to exacerbate seizures.
High intake of protein and GABA-containing foods can contribute to elevated levels. The metabolism and degradation of GABA requires a vitamin B6- dependent enzyme; therefore vitamin B6 deficiency can contribute to elevated GABA levels. Elevated plasma GABA levels have been observed in autistic children.
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