Choline is used to synthesize phospholipids, which are essential components of cell membranes. The phospholipid phosphatidylcholine is also important in packaging fat consumed in the diet. Without adequate phosphatidylcholine, fat and cholesterol may accumulate in the liver. In clinical trials, choline supplementation led to rapid fat and weight loss in female athletes. Phospholipids are precursors to cell signaling molecules such as diacylglyceride and ceramide. Cells use these molecules to communicate their current status and requirements. In addition to these two key functions, choline is a precursor to acetylcholine, a neurotransmitter involved in stimulating muscle contraction, maintaining circadian rhythms, enhancing memory, and other functions. Choline is a vital source of methyl groups that are required to methylate homocysteine. Choline is essential for optimal liver, muscle, and brain function.