Although choline has been the subject of nutritional research for almost 150 years, it is the newest official member of the B vitamin family, having its Adequate Intake levels (AIs) established for the first time by the National Academy of Sciences in 1998.
In the late 1930s, scientists discovered that pancreatic tissue contained a substance that could prevent fat accumulation in the liver. This substance was named choline, derived from the Greek word chole, which means bile. Since this initial discovery, researchers have found that choline is not only present in the pancreas and the liver, but is, in fact, a component of every human cell.
As research on choline has continued, it has been found that its naming after the Greek word for bile is highly appropriate. Choline has similar fat-modifying properties to bile, whose primary job is to emulsify fat so that it can be transported around the body in the blood, which is a water-based substance. Choline retains similar fat-modifying effects in the cellular membrane, allowing these membranes to operate with greater flexibility in handling both fat- and water-soluble compounds. In the absence of choline, many fat-based nutrients and metabolic waste products would not be able to pass in and out of the cells.
Choline’s unique chemical structure as a trimethylated molecule (having three attached methyl groups) allows it to have other important functions in the body since many important chemical events in the body are possible through the transfer of methyl groups from molecule to molecule. For example, genes can be switched on and off through methyl group transfer, making choline an important factor in the processes of cellular signaling. There is now special interest in choline in the area of mental health where the maintenance of messages sent between nerves is especially critical.
In Depth
Although choline has been the subject of nutritional research for almost 150 years, it is the newest official member of the B vitamin family, having its Adequate Intake levels (AIs) established for the first time by the National Academy of Sciences in 1998.
In the late 1930s, scientists discovered that pancreatic tissue contained a substance that could prevent fat accumulation in the liver. This substance was named choline, derived from the Greek word chole, which means bile. Since this initial discovery, researchers have found that choline is not only present in the pancreas and the liver, but is, in fact, a component of every human cell.
As research on choline has continued, it has been found that its naming after the Greek word for bile is highly appropriate. Choline has similar fat-modifying properties to bile, whose primary job is to emulsify fat so that it can be transported around the body in the blood, which is a water-based substance. Choline retains similar fat-modifying effects in the cellular membrane, allowing these membranes to operate with greater flexibility in handling both fat- and water-soluble compounds. In the absence of choline, many fat-based nutrients and metabolic waste products would not be able to pass in and out of the cells.
Choline’s unique chemical structure as a trimethylated molecule (having three attached methyl groups) allows it to have other important functions in the body since many important chemical events in the body are possible through the transfer of methyl groups from molecule to molecule. For example, genes can be switched on and off through methyl group transfer, making choline an important factor in the processes of cellular signaling. There is now special interest in choline in the area of mental health where the maintenance of messages sent between nerves is especially critical.
Function
Since choline is a critical component of many fat-containing compounds in the cell membrane, and the cell membrane is made up almost entirely of fats, the flexibility and integrity of the membrane is inextricably linked to adequate choline supplies. Phosphatidylcholineand sphingomyelin are examples of membrane structures that require choline. These fat-like molecules account for an unusually high percentage of total solids in the brain; therefore, choline is particularly important for the health of the brain and has significant potential for therapeutic use in brain disorders.
As noted in the Description section, choline has a unique chemical structure in that it is trimethylated (has three methyl groups), which makes it an extremely important molecule in methyl group metabolism. The transfer of methyl groups is a key process in allowing many important chemical events to occur in the body. For example, genes can be switched on and off through methyl group transfer, making choline an important factor in the processes of cellular signaling. Through its role in methyl group metabolism, choline plays a role in ensuring that levels of homocysteine are kept within healthy range (excess homocysteine levels are related to the development of cardiovascular disease and other health conditions).
Choline is a key component of acetylcholine, a neurotransmitter that carries messages between nerves and between nerves and muscles. Owing to its role in nerve-muscle function, choline supplemented in the form of lecithin or phosphatidlycholine has been used experimentally to help improve neuromuscular function in Alzheimer’s disease.
Deficiency: Causes and Symptoms
While poor dietary intake of choline can lead to choline deficiency, so can inadequate intake of three other nutrients – vitamin B3, folic acid and the amino acid methionine. All three nutrients are necessary for maintaining choline levels since they play a critical role in its synthesis, assisting it to obtain the three methyl groups that are an inherent part of its chemical structure. In addition to dietary causes, other factors that can contribute to choline deficiency include liver problems such as cirrhosis. Additionally, some hospital procedures including total parenteral nutrition, by-pass surgery and kidney transplant can lead to choline deficiency.
As a result of choline’s impact on homocysteine metabolism and the liver’s ability to package and transport fats efficiently, choline deficiency can manifest in symptoms associated with cardiovascular disease. Through participating in metabolic processes that allow homocysteine to be converted into other substances, choline plays a role in preventing the build-up of this damaging molecule that has been associated with increased risk of cardiovascular disease. A choline deficiency can prevent the liver from being able to package fats correctly, resulting in a disruption of normal lipid balance that manifests as decreased levels of VLDLs and increased levels of blood triglyceride levels.
Mild choline deficiency has also been associated with neurological manifestations such as memory problems, nerve-muscle imbalances and insomnia, as well as fatigue and the reduced ability of the kidneys to concentrate urine. Additionally, choline deficiency can cause a deficiency of the vitamin folate.
Extreme dietary choline deficiency is associated with a host of negative outcomes including liver dysfunction, impaired growth, abnormalities in bone formation, anemia, lack of red blood cell formation, kidney failure, hypertension, infertility, and both respiratory distress and failure to thrive in newborns. The consequences of hypertension and respiratory distress may be due to the reduction in levels of acetylcholine, the nervous system messenger molecule that cannot be synthesized without choline. The consequences of kidney failure and inadequate red blood cell formation may be due the reduction in levels of phosphatidylcholine, a cell membrane component that cannot be synthesized without choline.
Toxicity: Causes and Symptoms
Supplementation of choline in doses of 5-10 grams per day has been associated with blood pressure reduction as well as, in some individuals, feelings of dizziness and faintness. Higher doses, in the 10-15 gram range, have been linked with vomiting, increased salivation, sweating and unusual body odor, the latter symptom associated with the increased presence of trimethylamine, a choline breakdown product.
In 1998, the Institute of Medicine at the National Academy of Sciences set the Tolerable Upper Intake Levels (UL) for choline at 3.5 grams per day, based primarily upon its associated risk of reducing blood pressure.
Impact of Cooking, Storage and Processing
No consistent information is available on what effects cooking, storage and processing have upon the choline content of foods. Owing to its role in cellular membranes, choline may be susceptible to being able to be altered by heat and oxygen. Overcooking most choline-rich foods should be avoided in order to help preserve the nutrient’s content. One exception would be egg yolks since this choline-rich food carries too many safety risks when not properly cooked.
Drug-Nutrient Interactions
Medications that increase the risk of choline deficiency:
Choline, as well as a host of other nutrients, plays an instrumental role in a complicated chemical pathway known as the SAM (s-adenosyl-methionine) cycle. Therefore, the adequate status of choline is related to the adequate status of these other nutrients including vitamin B6, vitamin B12 and folate; the amino acids serine and glycine; and the molecules betaine, ethanolamine and sarcosine.
While choline is dependent upon all of these molecules, it is folate deficiency that is most likely to disrupt the SAM cycle balance and therefore impact choline status as well. In the SAM cycle, the molecules listed above are continually exchanging components, especially chemical structures called methyl groups. This is done in order to ensure that the body is supplied with adequate amounts of SAM. One of the functions of choline in the SAM cycle is to keep methyl groups cycling for their eventual donation to SAM. Since folic acid plays a critical role in the movement of these methyl groups, it is integrally linked to SAM cycle balance and choline status.
Health Conditions
Individuals who have the following health conditions should pay special attention to their choline status:
Choline, like the other SAM cycle nutrients, may also play a role in reducing the toxic effects of heavy metals, including lead, upon the body. While choline’s precise role in helping to protect against heavy metal toxicity is still not clear, the process is likely to be complex and to involve more than just the simple methylation of heavy metals since the addition of a methyl group to heavy metals often increases, rather than decreases, their toxicity.
Form in Dietary Supplements
Food Sources
Lecithin (phosphytidylcholine),the emulsifier that is added to foods to keep their components blended together, is the richest source of choline in the U.S. diet. Soybeans are the source of most of the lecithin in the U.S. food supply.
Food sources of choline include soybean and soybean products, egg yolk, butter, banana, barley, cauliflower, corn, flax seeds, lentils, milk, oranges, potatoes, sesame seeds, tomatoes and whole wheat bread. Many of these foods do not just contain choline itself, but also other forms of the nutrient including lecithin (phosphatidylcholine) and sphingomyelin.
Public Recommendations
In 1998, the Institute of Medicine at the National Academy of Sciences set the following Adequate Intake (AI) levels for choline:
Prevention of liver damage was the main criterion used in establishment of these recommended levels.
References