Source

Phosphatidylserine is produced internally in the body from phospholipid building blocks. It is present in trace amounts in rice, soy, and green leafy vegetables. Small amounts are also present in lecithin.

Synthesized PS is primarily derived from soy but has been sourced from bovine (cow) brain tissue in the past. Animal derived PS is quite rare today. Nevertheless, vegetarians and vegans who choose to supplement with PS should ensure their preparation is derived from a vegetable source.