Phosphatidylcholine (PC) is an essential part of human cell membranes and an important dietary source of choline, an important biochemical. Its common name is lecithin. It can be made from phosphatidylethanolamine (PE) by methylation of the ethanolamine moiety in a reaction catalyzed by phosphatidylethanolamine N-methyltransferase. There is a decrease in phosphatidylethanolamine (PE) and ether-linked PC concentrations, as well as an increase in lysophosphatidylethanolamine during chronic stress. PC and choline are important for healthy brains, hearts, skeletal muscles, livers and metabolism. For example, Alzheimer’s disease patients have lower concentrations of three different PCs in their blood serum than healthy control subjects. Choline is important in maintaining cell structure and synthesizing the neurotransmitter acetylcholine. Choline supplementation during critical periods of neonatal development can have long-term beneficial effects on memory. A lack of sufficient dietary choline can cause signs of subclinical organ dysfunction (fatty liver or muscle damage). The need for choline is especially high during pregnancy and lactation. If there is insufficient choline stored in the body, the ability to methylate homocysteine to make methionine decreases, and plasma concentrations of homocysteine increase. This can increase the risk for cardiovascular disease, cancer, cognitive decline and bone fractures. On the other hand, over-consumption of red meat and other dietary sources of PC can lead to the production of trimethylamine oxide (TMAO) by gut bacteria. TMAO is both a kidney toxin and a biomarker for kidney diseases. So, PC and choline must be present in sufficient concentrations to support life, but not be too high to be toxic. Moreover, not everybody is equally susceptible to TMAO toxicity. People who have a kidney disease or are highly susceptible to cardiovascular disease may want to restrict their consumption of red meat and egg yolks, as well as avoid lecithin dietary supplements. Still, vegetarians who don’t eat egg yolks may want to take such supplements. On the other hand, another supplement called citicoline (cytidine diphosphocholine, CDP-choline) may be a better option since it is not metabolized into TMAO and may help brain function. Citicoline supplementation may improve memory, including verbal memory in patients with age related cognitive impairment, as well as improving cognitive function in elderly patients with vascular related mild cognitive impairment.