Discussion
Choline has been defined as an essential nutrient, with daily adequate intake (AI) values for healthy adult men of 550 mg according to NAM [All water-soluble supplements rapidly and similarly increased D9-choline and D9-betaine plasma levels, with maximum concentrations achieved at 0.5–1 h. This is consistent with the results on single administration of an AI dosage of unlabeled choline supplements in adults [The increase in plasma D9-choline concentration after D9-POPC administration, however, was different in two ways. First, plasma concentrations increased later, peak concentrations were delayed from 0.5–1 h to ~ 1.5 h and the peaks were broader, indicating different mechanisms of D9-choline assimilation from lipidic D9-POPC. Such more retarded and longer lasting increase may be of benefit for achieving a balanced increase in plasma choline concentrations. After ingesting the AI value of choline (550 mg) in the form of egg-PC (4012 mg), maximum values of plasma choline were delayed to 3 h, but maximum concentrations were similar to water-soluble choline components. This discrepancy may be due to the higher dosage of ~ 7 mg/kg choline in our previous study, compared to 2.7 mg/kg D9-choline equivalent used here as a tracer, and the higher sensitivity of metabolic follow-up using deuterium-labelled compared to native compounds [Second, the maximum value and AUC of plasma D9-choline were lower after D9-POPC compared to water-soluble D9-choline components. It was suggested that lyso-PC is only partly degraded to free choline within the enterocytes, whereas ~ 50% are re-synthesised to PC, using available coenzyme A-activated fatty acids (acyl-CoA) and lyso-PC acyltransferases (LPCAT) [