Glycerophosphocholine (GPC) is the primary form of choline that occurs in milk. It's purposed as a cognitive enhancer, but the molecule yields different products after metabolism, with a distribution beyond the brain.
The dose used below, extrapolated to humans, would be something like 1 g/70 kg, which isn't too crazy:
"In supplements, choline has most often been used by adults in doses of 1-3 grams by mouth daily for up to 4 months."
"aGPC was labelled with [14C]-glycerol ([14G]-GPC) or [14C]-choline ([14C]-GPC)."
"Both labelled compounds gave a wide distribution of radioactivity, particularly concentrated in the liver, kidney, lung and spleen compared to blood."
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"After oral administration, the main circulating metabolite was choline (after [14C]-GPC); intact a-GPC was not present after either labelled compound although there were the same unknown metabolites as after i.v. injection."
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"[..]choline and/or its anabolites enter the brain and is reused for biosynthesis of phospholipids. This was confirmed by chromatography of the phosphatidylcholine fraction of the brain homogenates after hydrolysis with phospholipase C. As in blood, this hydrolysis resulted in formation of choline phosphate."
"By far, the largest part of the administered radioactivity was exhaled as 14CO2, in accordance with established catabolic pathways of glycerol (i.e. glycolysis) and choline degradation."
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