Choline is a versatile nutrient involved in various metabolic processes within the human body. Despite its ability to be synthesized in the liver, dietary intake is necessary to meet the body's requirements.
This article delves into the metabolic pathways and processes involving choline, highlighting its significance in maintaining health.
Biosynthesis and Absorption
In humans, choline is synthesized via the phosphatidylethanolamine N-methyltransferase (PEMT) pathway, although this biosynthesis is insufficient to meet the body's needs. The PEMT route involves the conversion of phosphatidylethanolamine to phosphatidylcholine, a process that requires three methyl groups from S-adenosylmethionine (SAM).
Choline is absorbed from the intestines through the SLC44A1 membrane protein via facilitated diffusion. This process is governed by the choline concentration gradient and the electrical potential across enterocyte membranes. Absorbed choline enters systemic circulation through the portal vein, while unabsorbed choline is degraded by gut microbes to trimethylamine.
Transport and Storage
Choline is transported in the blood as a free ion and in the form of choline-containing phospholipids. Blood plasma choline levels are regulated, but intake and deficiency can alter these levels. Choline requires transporters to pass through cell membranes, with three types known: SLC5A7, CTLs, and OCTs.
Choline is stored in cell membranes and organelles as phospholipids, including phosphatidylcholines and glycerophosphocholines. These storage forms are crucial for maintaining cellular structure and function, emphasizing choline's importance in health.
Excretion and Health Implications
Choline excretion is minimal, even at high doses, with trimethylglycine being demethylated in the liver and kidneys to dimethylglycine. Excessive choline intake can lead to adverse effects, such as low blood pressure and fish-like body odor due to trimethylamine formation.
Choline deficiency can cause non-alcoholic fatty liver disease and muscle damage, highlighting the importance of adequate intake. Estrogen production and genetic factors can influence choline metabolism, affecting dietary needs and health outcomes.
