Phosphatidylcholine

Phosphatidylcholine is a glycerophospholipid, meaning a molecule built on a glycerol backbone carrying two fatty acids and a phosphate group that is capped by the nutrient choline ^[1]. It is a principal structural lipid of the membranes that enclose plant and animal cells, where it is concentrated in the outer layer of the bilayer, and it is the main phospholipid making up lecithin ^[1][2]. A particular form rich in two saturated fatty acids, dipalmitoyl phosphatidylcholine, is the key surface-active lipid of the surfactant that keeps the lungs open ^[2].

Phosphatidylcholine is readily obtained from egg yolk, soybeans, and sunflower, the sources of commercial lecithin, and it has long been familiar to chemistry; the French chemist Theodore Gobley isolated lecithin from egg yolk in the nineteenth century and named it from the Greek word for egg yolk ^[1].

Biologically, phosphatidylcholine is the body's largest reservoir of choline, and together with sphingomyelin it holds the great majority of the body's choline ^[2]. From this pool choline can be drawn to make the neurotransmitter acetylcholine and, by way of betaine, to supply methyl groups for many methylation reactions ^[1]. Phosphatidylcholine is also required in the liver to assemble and secrete very-low-density lipoprotein, which is why a shortage of choline or phosphatidylcholine leads to fat accumulation in the liver ^[1][2]. It is a major constituent of bile and is synthesized by two routes: the CDP-choline pathway found in most tissues and a second pathway in the liver that methylates phosphatidylethanolamine ^[1].

Its uses and research span nutrition and medicine. As a source of choline it is taken as a dietary supplement, and choline deficiency is a recognized contributor to the liver disease that can accompany long-term intravenous (parenteral) nutrition, prompting study of choline and phosphatidylcholine supplementation ^[2]. In ulcerative colitis, delayed-release phosphatidylcholine improved disease activity in randomized trials, an effect attributed to restoring the protective phospholipid layer of the intestinal mucus ^[3]. Circulating phosphatidylcholine and related choline metabolites have been linked in genetic studies to a range of health outcomes ^[4], while evidence for some popular uses, such as dementia, is considered insufficient, and its use in injectable fat-dissolving procedures is not an established substitute for surgery. Lecithin and phosphatidylcholine are generally handled as food ingredients and supplements rather than as licensed drugs ^[4].

Very safe for most people, with occasional GI upset, sweating, or a fishy body odor at high doses from choline metabolism. High choline intake has been discussed in relation to TMAO and cardiovascular markers, though the practical significance is debated. No major interactions at normal doses.