Temperament
An increase in temperament with age may be partly caused by changes in bacterial groups in the intestines. After all, aging, unhealthy diet, stress, drugs, medications, are responsible for bacteria groups producing less and less neurotransmitters in the intestines. They are known to play a role against depression. Other substances produced by bacteria in the gut that have a similar effect include glutamate, butyrate, serotonin and gamma aminobutyric acid.
Gnostotheca 6730