Choline: An Essential and Dangerous Nutrient
This series of two articles is speculative. It is not written by a medical professional and does not present medical advice. Consult with your provider before changing any aspect of your lifestyle or diet.
The first article in this series summarizes the nutritional value of choline and the danger associated with its dietary consumption. The second article in this series presents a solution to the predicament.
To watch the companion video to this series, click here.
CHOLINE IS A VITAMIN
Choline deficiency causes cellular apoptosis. It is also the only known nutritional deficiency that directly causes cancer in the absence of carcinogens - specifically, it causes hepatocellular carcinoma. Despite these metabolic effects being known by the 1980’s, it was not until the late 1990’s that choline was recognized as an essential nutrient. Essential nutrients, many of which are called vitamins, are classically defined by a clear and consistent pathology that develops in a deficiency state.
In the case of choline, the pathology takes the form of fatty liver disease and steatosis of the liver. Studies on people fed parenteral nutrition (liquid nutrition given intravascularly) by Alan Buchman revealed that patients lacking choline in their diet developed fatty liver disease that would progress to steatosis within weeks. When choline was added back to the diet, the liver would heal and return to normal function.
For a more detailed review on the academic discovery of the essential role of dietary choline, read my article here.
CHOLINE, METHYLATION, AND HEALTH
The most well-known impact of the proliferation of genome wide association studies in public discourse has been the recognition that humans have widely varying abilities to methylate molecules. Methylation, also called one-carbon metabolism, is an integral biochemical process by which molecules are transformed structurally. In the major methylation pathway, homocysteine is recycled back into methionine through methylation. People with polymorphisms at the PEMT, MTHFD1, BHMT, MTHFR, MTR, MTRR, SLC19A1, COMT, and SHMT1 genes may have impaired ability to methylate molecules.
When methylation is impaired, blood homocysteine levels remain elevated – a condition known as hyperhomocysteinemia. Hyperhomocysteinemia is strongly associated with atherosclerosis, heart failure, and Alzheimer’s disease. For people with impaired ability to methylate (particularly at the notorious MTHFR gene), a prudent way to reduce the methylation demands on their body includes supplementing with creatine and phosphatidylcholine. In particular, the synthesis of phosphatidylcholine from phosphatidylethanolamine via the liver enzyme phosphatidylethanolamine N-methyltransferase (PEMT) comprises a large portion of the methylation demands of the human body .
By reducing demands on the methylation system and allowing the body to metabolize homocysteine, dietary consumption of phosphatidylcholine may reduce risks of cardiovascular and neurodegenerative disease. Polymorphisms that impair methylation are also associated with depression, anxiety, and cognitive function, as is the resulting condition, hyperhomocysteinemia. Consequently, it is reasonable to speculate that phosphatidylcholine supplementation may improve well-being and cognitive performance, in addition to cardiovascular health.
CHOLINE THE NEUROTRANSMITTER
In addition to choline’s roles in cellular health, liver health, cardiovascular health, and mental health, choline plays a crucial role in cognitive performance via the neurotransmitter acetylcholine. Acetylcholine is synthesized from dietary choline. It is such an impactful neurotransmitter on memory and learning that the primary symptom-management medications for Alzheimer’s disease are inhibitors of the enzyme that degrades acetylcholine in the brain, acetylcholinesterase.
As I have written a series of articles on acetylcholine, which you can access here, I will not get into the details of the neuroscience of acetylcholine in this article. For our purposes, it is sufficient to recognize that nutritional choline plays an important role in brain function.
THE PROBLEM WITH EATING CHOLINE
Unlike the other major reducer of methylation demands, creatine, the consumption of dietary choline comes with a cost. Though dietary choline is associated with a lower risk of stroke, lower mortality from cardiovascular disease, lower inflammatory markers (including C-reactive protein, interleukin-6, and tumor necrosis factor alpha), in 2011, it was discovered that the metabolism of phosphatidylcholine by gut microbiota could present significant cardiovascular disease risk.
In one of the most cited papers of the last decade, Wang et al. showed that gut microbiota cleave trimethylamine (TMA) from dietary phosphatidylcholine, subsequent to which TMA is oxidized by the liver enzyme flavin monooxygenase 3 (FMO3) into trimethylamine N-oxide (TMAO). The research team found that systemic TMAO levels were strongly associated with atherosclerosis and cardiac risk. Subsequent studies have confirmed these initial findings and linked TMAO to venous thrombosis, diabetes and colorectal cancer. (Interestingly, rodent studies indicate that androgens may reduce systemic TMAO by reducing the expression of the enzyme FMO3, while resveratrol has been shown to reduce TMAO by remodeling the gut microbiome).
The predicament with TMAO was most prominently introduced to public discourse in a well-publicized debate between a vegan and an omnivore on the Joe Rogan Experience podcast. Subsequently, vegans have used the TMAO argument to encourage the public to reduce their consumption of animal products, which often contain both choline and L-carnitine, a nutrient found in red meat that was also shown to be metabolized into TMAO by the same research team. Though not the subject of this article, it is worthwhile to note that L-carnitine has also been shown to improve cognitive function in neurodegenerative disease models and is one of the only methods that has been shown to reduce plasma lipoprotein (a) levels, a major risk factor for cardiovascular disease.
To read the second and final article in this series, click here.
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