Dihydrogencitrate

Synopsis

Choline Dihydrogen Citrate (Choline Dihydrogencitrate)

1. Identity and Chemical Characterization

Choline dihydrogen citrate — also written as choline dihydrogencitrate — is the principal dietary supplement and pharmaceutical compound referred to by the colloquial name "dihydrogencitrate" in nutritional and nutraceutical contexts. It is the 1:1 salt formed by the combination of the quaternary ammonium compound choline with citric acid, and it serves as one of the established salt forms in which choline is delivered in medicinal and supplemental preparations.

The compound has the molecular formula C₁₁H₂₁NO₈ and a molecular weight of 295.29 g/mol. Its IUPAC-derived chemical name is ethanaminium, 2-hydroxy-N,N,N-trimethyl-, 2-hydroxy-1,2,3-propanetricarboxylate (1:1), also described as (2-hydroxyethyl)trimethylammonium dihydrogen citrate, and it carries the CAS Registry Number 77-91-8.

Its chemical name is 2-hydroxyethyl-trimethyl-ammonium citrate (CAS No. 77-91-8; EINECS 201-068-6). The compound is a white crystalline powder with a melting point of 103–108 °C, a bulk density of 0.55–0.70 g/mL, and high water solubility (approximately 360 g per 100 g of water at 25 °C). Its pH in a 10% aqueous solution falls in the range of 3.5–4.5.

Choline dihydrogen citrate is part of a class of quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation and the dihydrogen citrate counteranion. The compound is listed and monographed under the synonym Choline Citrate in the United States Pharmacopeia (USP) and appears in the British Pharmacopeia (BP) and European Pharmacopeia (EP). The USP monograph specifies that Choline Citrate must contain not less than 97.0% and not more than 103.0% of choline dihydrogen citrate (C₁₁H₂₁NO₈), calculated on the as-is basis.

Australia's Therapeutic Goods Administration (TGA) lists choline dihydrogen citrate as a permitted ingredient in listed medicines, referencing both the British Pharmacopoeia (BP) and the United States Pharmacopoeia (USP) as governing standards.

Common Synonyms

Choline citrate
Choline dihydrogencitrate salt
(2-Hydroxyethyl)trimethylammonium citrate
Trade and proprietary synonyms have included: Delichol, Citracol, Cholinvel, Colicitrin, Cirrocolina, Citracholine, and Chothyn.

Pharmacopeial Forms and Physical Grades

Choline dihydrogen citrate is used in sport nutrition, juices and beverages, food supplements, over-the-counter (OTC) products, clinical nutrition, and pharmaceutical preparations, and complies with USP monograph specifications. It is commercially supplied as a white crystalline powder, and some manufacturers provide grades conditioned with silicon dioxide to improve flowability and prevent caking.

2. Natural Source and Endogenous Context

Choline dihydrogen citrate is a manufactured salt form of choline, combining a ubiquitous biological nutrient — choline — with citric acid, a naturally occurring organic acid found throughout the plant and animal kingdoms. The salt form does not itself occur in nature; rather, free choline and its various esters are the naturally occurring species.

Choline is a nutrient found in many foods. The brain and nervous system require it to regulate memory, mood, and muscle control, among other functions. It is also required to form the membranes that surround the body's cells. The body can make a small amount of choline in the liver, but most of the choline in the body comes from food.

Dietary choline is present in multiple different forms that are both water-soluble (e.g., free choline, phosphocholine, and glycerophosphocholine) and lipid-soluble (e.g., phosphatidylcholine and sphingomyelin). Choline dihydrogen citrate, as a water-soluble supplemental salt, sits alongside choline chloride and choline bitartrate as a principal means of delivering exogenous choline in pharmaceutical and nutraceutical contexts.

Choline dihydrogen citrate is formed when choline is combined with citric acid. This increases its bioavailability, making it easier to absorb and more effective. The claim of enhanced bioavailability relative to other choline salts has been made by manufacturers but, as of current literature, has not been rigorously tested in controlled human bioavailability studies specific to this salt form compared with choline bitartrate or choline chloride.

3. Historical and Medical Use

Choline itself has a history of medical and nutritional interest predating modern biochemistry, but choline dihydrogen citrate as a specific pharmaceutical preparation emerged in the mid-twentieth century.

By the early twentieth century, lecithin was being studied for its health benefits, particularly after Charles Best's work in the 1930s showed it could prevent fatty liver in dogs, with choline identified as the active component. Choline chloride's therapeutic potential was recognized in the 1930s after research demonstrated its efficacy in preventing fatty liver in animal models, leading to its exploration for liver conditions such as cirrhosis by the mid-twentieth century and inclusion in infant formulas by the 1970s.

Choline dihydrogen citrate as a discrete preparation entered the medical literature in 1947. An article titled "Choline Dihydrogen Citrate in Infantile Biliary Cirrhosis" was published in the Indian Medical Gazette in December 1947 by S. Balasundaram, Director of the Ehrlich Laboratory in Madras (present-day Chennai), India. This represents the earliest known clinical report of the compound in a named therapeutic context.

Shortly thereafter, choline dihydrogen citrate was described under a listing titled "New and Nonofficial Remedies: Choline Dihydrogen Citrate" in the Journal of the American Medical Association on 1 July 1950 (vol. 143, no. 9, p. 815). This listing in JAMA under "New and Nonofficial Remedies" was a formal mechanism by which the American Medical Association's Council on Pharmacy and Chemistry evaluated and recognized emerging therapeutic agents in mid-century American medicine, indicating that the compound had attracted sufficient clinical and commercial attention to merit official scrutiny.

Choline bitartrate's therapeutic applications emerged in the 1970s and 1980s for cognitive and neurological conditions like Alzheimer's disease, and by the 1990s it was widely used in dietary supplements for cognitive enhancement and liver support. The same historical arc applies broadly to choline dihydrogen citrate, which, as a pharmacopeially equivalent choline salt, tracked similar applications in the latter decades of the twentieth century.

4. Active Compounds and Mechanisms of Action

Choline dihydrogen citrate is primarily a delivery vehicle for choline (the cationic component), with citrate (the anionic component) serving as an organic counter-ion. Upon oral ingestion, the salt dissociates in the gastrointestinal tract, releasing free choline for absorption. The biological activity of the compound is therefore principally attributable to choline, with potential secondary contributions from the citrate anion, which participates in intermediary metabolism.

Choline as the Active Moiety

Adequate daily intake of choline has been established by the US National Academy of Medicine in 1998, considering choline requirements for different ages, sex differences, and physiological states, including pregnancy.

By serving as a precursor for acetylcholine and phospholipids, choline is important for cholinergic transmission and the structural integrity of cell membranes. In addition, choline is involved in lipid and cholesterol transport and serves as a methyl donor after oxidation to betaine.

Choline is a micronutrient and methyl donor required for normal brain growth and development. It plays a pivotal role in maintaining structural and functional integrity of cellular membranes. It also regulates cholinergic signaling in the brain via the synthesis of acetylcholine. Via its metabolites, it participates in pathways that regulate methylation of genes related to memory and cognitive functions at different stages of development. Choline-related functions have been dysregulated in some neurodegenerative diseases, suggesting choline's role in influencing mental health across the lifespan.

Acetylcholine Synthesis

Choline is converted into a neurotransmitter called acetylcholine, which helps muscles to contract, activates pain responses, and plays a role in brain functions of memory and thinking. Choline is the precursor for the neurotransmitter acetylcholine, which is involved in many functions including memory and muscle control.

Phospholipid Metabolism and Membrane Integrity

Most choline is metabolized in the liver where it is converted into phosphatidylcholine, which assists in building fat-carrying proteins and breaking down cholesterol. The production of very low-density lipoproteins requires phosphatidylcholine synthesis in the liver. Without an adequate supply of choline for phosphatidylcholine synthesis, triacylglycerides will accumulate, which leads to a fatty liver condition.

Methyl Group Donation

Choline supports methyl group metabolism, serving as a precursor for S-adenosylmethionine, a critical methyl donor in the body. This methylation process helps maintain normal homocysteine levels.

Epigenetic and Neurodevelopmental Signalling

Choline can modify gene methylation and expression, and thereby alter neuronal activity. Evidence from clinical and preclinical studies confirms that maternal choline intake is critical for neurogenesis, cognition, and visual system development, and that higher choline availability buffers the fetal brain against environmental and psychosocial stressors.

Emerging Signalling Role: Sigma-1 Receptor

While choline's signaling role has been considered mostly indirect via acetylcholine and phosphatidylcholine, which are synthesized from choline, emerging evidence supports a role for choline as an intracellular messenger acting on Sigma-1R, a non-opioid intracellular receptor. These new findings expand the cell signaling repertoire and increase the current understanding of the role of choline while warranting more research to uncover the molecular mechanisms and significance.

The Citrate Moiety

The dihydrogen citrate counterion contributes citrate, an intermediate of the tricarboxylic acid (Krebs) cycle. Citrate lies at a critical node of metabolism, linking tricarboxylic acid metabolism and lipogenesis via acetyl-coenzyme A. The physiological contribution of the citrate anion released from this salt at supplemental doses remains incompletely characterized in human studies specific to this compound.

TMAO Production: A Documented Metabolic Effect

The intestinal microbiota is directly implicated in the generation of trimethylamine from dietary choline and its metabolite phosphatidylcholine, as well as from dietary betaine and carnitine. Trimethylamine is subsequently converted into TMAO (trimethylamine N-oxide) by flavin-containing monooxygenases in the liver. Choline consumption has been shown to increase production of TMAO, a substance that has been linked to a higher risk of cardiovascular disease, in a dose-dependent manner in adults. The significance of TMAO as a causal risk factor versus a biomarker remains an area of active scientific debate.

5. Body Systems and Health Areas of Association

Choline has important roles in neurodevelopment, cognition, liver function, lipid metabolism, and cardiovascular health. As the bioavailable choline salt form underlying choline dihydrogen citrate, its areas of supplemental application map directly to these physiological roles.

5.1 Neurological and Cognitive Function

The effect of dietary choline availability on brain development and function is widely accepted since animal and human research has provided evidence supporting the neuroprotective and cognitive-enhancing effects of choline dietary supplementation at different developmental stages. A systematic review of rodent studies performed during the last two decades indicates that cognitive improvement induced by choline supplementation has mainly been attributed to enhanced cholinergic neurotransmission in the hippocampal system.

However, the translation to clinical benefit in humans is less certain. Other studies have shown that choline supplements do not improve cognition in healthy adults or in patients with Alzheimer's disease, Parkinson's disease dementia, or other memory problems. More research is needed to understand the relationship between choline intakes and cognitive function as well as to find out whether choline supplements offer any benefit to patients with dementia.

In the specific area of fetal alcohol spectrum disorder (FASD), higher-quality evidence is emerging. A review collating evidence from 22 human clinical and preclinical studies concluded that choline supplementation has the potential to ameliorate some of the behavioral, cognitive, and neurological deficits observed in offspring exposed to alcohol in utero. Choline supplementation improves cognitive outcomes in fetal alcohol spectrum disorder and mitigates neurodegenerative pathology in Alzheimer's models. These findings are largely from preclinical models and early-phase clinical studies, and should be considered preliminary.

5.2 Liver Health

The hepatoprotective role of choline is one of the most robustly established facets of its biology. The primary criterion used to estimate the Adequate Intake (AI) for choline is the prevention of liver damage as assessed by measuring serum alanine aminotransferase levels.

There is a link between choline deficiency and liver disease. Phosphatidylcholine carries fats away from the liver, so a choline deficiency can cause the liver to store too much fat. There may be a link between low intakes of choline and the risk of developing non-alcoholic fatty liver disease (NAFLD), a condition in which fat builds up in the liver of people who do not drink excessive amounts of alcohol. It is a common liver disorder, especially in people who are overweight or have obesity. Getting enough choline is necessary for proper liver function and to prevent NAFLD. However, more research is needed to better understand how choline might help prevent or treat NAFLD.

Healthy men with normal folate and vitamin B12 status fed a choline-deficient diet developed liver damage, and de novo synthesis of choline was not adequate to meet the demand for the nutrient. Similar alterations have been reported in patients receiving long-term total parenteral nutrition devoid of choline.

5.3 Neurodevelopment and Pregnancy

An adequate dietary intake of choline during pregnancy supports proper fetal development, and throughout life supports brain, liver, and muscle functions, while choline deficiency is linked to disease states like fatty liver.

Data from animal models show that higher intakes of choline during gestation and the perinatal period can protect against brain damage and cognitive/neurological declines associated with epilepsy and certain hereditary conditions, such as Down Syndrome and Rett Syndromes. Human clinical evidence is still accumulating in these areas.

5.4 Muscle Function

Depletion of choline during adulthood has been linked to organ or cellular dysfunction including nonalcoholic fatty liver, liver damage, muscle damage, lymphocyte apoptosis, and DNA damage. More research is needed on the clinical consequences of choline supplementation in human skeletal muscle structure and function, as evidence supporting its relevance comes mainly from basic research.

5.5 Cardiovascular Health

The relationship between choline supplementation and cardiovascular health is bidirectional and complex. In cardiometabolic health, recent data challenge the interpretation of TMAO as a causal toxin, positioning it instead as a marker of renal function. Separately, higher dietary choline intakes have been associated with metabolic risk signals. In three large cohorts of men and women, higher intakes of phosphatidylcholine were associated with an increased risk of type 2 diabetes mellitus (T2DM). Those who had the highest dietary intakes of choline showed a 34% increased risk of T2DM compared with the lowest intakes. The exact mechanism of this association is unclear and warrants further research.

6. Scientific Evidence by Area of Use

It should be noted at the outset that the clinical evidence base for choline dihydrogen citrate specifically — as distinct from other choline salt forms — is limited. The majority of human clinical studies on choline supplementation have used choline bitartrate, choline chloride, phosphatidylcholine, or CDP-choline (citicoline). Because these are all sources of the same choline cation, findings on choline pharmacology and deficiency/repletion are extrapolated to choline dihydrogen citrate in clinical and regulatory practice. The summaries below reflect this broader choline evidence base.

6.1 Non-Alcoholic Fatty Liver Disease (NAFLD)

Evidence strength: Moderate for deficiency as a causal factor; preliminary for supplementation as treatment.

The link between choline deficiency and fatty liver is well established from controlled dietary deprivation studies. Zeisel et al. provided the first controlled demonstration that consuming a choline-deficient diet for three weeks led to a 30% reduction in plasma choline and a significant rise in serum alanine aminotransferase (ALT) activity, indicating liver injury. However, whether supplementation with choline salts can reverse or treat established NAFLD in humans beyond correcting frank deficiency is an open question, and no large, well-controlled randomized trials specific to choline dihydrogen citrate have been published.

6.2 Cognitive Function and Neurodegeneration

Evidence strength: Preclinical evidence strong; human RCT evidence mixed and insufficient for firm conclusions.

The early historical use of choline dihydrogen citrate — as documented in a 1950 JAMA listing — included conditions such as memory loss and cognitive disorders. Modern research has not uniformly validated this application. Studies have shown that choline supplements do not improve cognition in healthy adults or in patients with Alzheimer's disease, Parkinson's disease dementia, or other memory problems, and more research is needed to understand the relationship between choline intakes and cognitive function.

In the area of neurodevelopment, where choline adequacy during sensitive windows of brain formation appears especially important, the evidence is more convincing but primarily observational or from animal studies. A review of 22 human clinical and preclinical studies concluded that choline supplementation has the potential to ameliorate some of the behavioral, cognitive, and neurological deficits observed in offspring exposed to alcohol in utero.

6.3 Liver Disease (Early Clinical Reports)

Evidence strength: Historically suggestive; modern RCT evidence absent for this specific salt form.

The specific compound choline dihydrogen citrate was reported in a case series context in 1947 by Balasundaram, who described its use in infantile biliary cirrhosis in Indian medical practice. This represents early observational/clinical use rather than a controlled trial, and no randomized controlled trials with choline dihydrogen citrate in biliary or other liver conditions are retrievable in the current scientific literature. The broader choline-liver connection, however, is well supported by mechanistic and epidemiological data.

6.4 Neurodevelopment in Fetal Alcohol Spectrum Disorders

Evidence strength: Early clinical and preclinical; promising but not yet definitive.

Evidence from clinical and preclinical studies confirms that maternal choline intake is critical for neurogenesis, cognition, and visual system development, and that higher choline availability buffers the fetal brain against environmental and psychosocial stressors. Controlled clinical trials examining choline supplementation in FASD have been conducted using choline chloride rather than choline dihydrogen citrate specifically.

6.5 Choline Status and General Population Deficiency

Evidence strength: Well-established epidemiologically.

A study suggests that daily consumption of choline by adults in the United States (mean = 312 mg/day for men and 314 mg/day for women) is significantly below the recommended adequate daily intake of 550 mg/day for men and 425 mg/day for women. This widespread shortfall underpins the commercial rationale for choline supplementation in forms including choline dihydrogen citrate.

7. Dosage Forms and Reported Dosages

Choline is available as a dietary supplement as choline chloride or choline bitartrate and as lecithin. In treatment of neurological diseases, large doses of 5 to 30 g of choline and phosphatidylcholine have been administered to humans. Choline dihydrogen citrate is an additional pharmacopeially recognized supplemental form within this landscape.

The Adequate Intake (AI) for adults is 550 mg/day of choline for men and 425 mg/day for women. Adequate intakes were established at 550 mg/day for adult men, 425 mg/day for adult women, 450 mg/day for pregnant women, and 550 mg/day during lactation.

The Tolerable Upper Intake Level (UL) for adults is 3.5 g/day. In 1998, the Institute of Medicine recognized choline as an essential nutrient and set the Adequate Intake (AI) at 550 mg/day and 425 mg/day for men and women 19 years of age and older, respectively. These levels were set based on the dietary intakes of the U.S. population, and on the development of liver damage seen with lower intake.

For infants, specific AI values have been established: for infants aged 0–6 months, the AI is approximately 18 mg/kg/day (125 mg/day); for infants aged 7–12 months, it is approximately 17 mg/kg/day, corresponding to 150 mg/day of choline.

Choline dihydrogen citrate is formulated in several delivery forms:

Powder / crystalline bulk: for dissolution in water or incorporation into beverages and functional foods.
Tablets and capsules: solid oral dosage forms for both pharmaceutical and nutraceutical applications, including OTC choline supplements.
Clinical nutrition formulas: incorporated into specialized enteral and parenteral preparations.
Sports nutrition products and functional beverages: used as a choline source in sport nutrition, juices, and beverage formulations.

In terms of choline content by weight, choline dihydrogen citrate (molecular weight 295.29) contains a lower proportion of free choline per gram than choline chloride (molecular weight 139.62) or choline bitartrate (molecular weight 253.27), meaning that larger gravimetric doses of the salt are required to deliver equivalent amounts of elemental choline.

8. Safety Considerations and Interactions

8.1 Adverse Effects at High Doses

High intakes of choline are associated with a fishy body odor, vomiting, excessive sweating and salivation, hypotension, and liver toxicity. Choline consumption has been shown to increase production of TMAO, a substance that has been linked to a higher risk of cardiovascular disease.

The critical adverse effect from high intake of choline is hypotension, with corroborative evidence on cholinergic side effects (e.g., sweating and diarrhea) and fishy body odor.

8.2 Tolerable Upper Intake Level (UL)

The Food and Nutrition Board (FNB) has established Tolerable Upper Intake Levels (ULs) for choline from food and supplements based on the amounts of choline that are associated with hypotension and fishy body odor. The ULs apply to healthy children and adults but not to those taking high doses of choline under medical supervision. The FNB was unable to establish ULs for infants due to the lack of data on adverse effects in this age group, and breast milk, formula, and food should be the only sources of choline for infants.

8.3 TMAO and Cardiovascular Risk Signal

The intestinal microbiota is directly implicated in the generation of trimethylamine from dietary choline and its metabolite phosphatidylcholine, as well as from dietary betaine and carnitine. Trimethylamine is subsequently converted into TMAO by flavin-containing monooxygenases in the liver. Elevated circulating TMAO has been associated with adverse cardiovascular outcomes in epidemiological research, though whether choline supplementation at recommended doses drives clinically meaningful elevations in TMAO — and whether TMAO is a causal agent or a confounding biomarker — is subject to ongoing scientific debate. Recent data challenge the interpretation of TMAO as a causal toxin, positioning it instead as a marker of renal function.

8.4 Drug Interactions

Choline is not known to have any clinically relevant interactions with medications. However, given that choline participates in acetylcholine synthesis, theoretical caution applies in the context of cholinomimetic or anticholinesterase medications (e.g., acetylcholinesterase inhibitors used in dementia), as the pharmacodynamic effects of those agents could be enhanced. This theoretical interaction is not specifically documented for choline dihydrogen citrate in the reviewed literature.

8.5 Regulatory Status

Australia's Therapeutic Goods Administration (TGA) recognizes choline dihydrogen citrate (CAS 77-91-8) as a permitted ingredient in listed medicines. In the United States, it is covered under the USP monograph for Choline Citrate and is used in dietary supplement products as a recognized source of choline. In the European Union and United Kingdom, it complies with the British Pharmacopoeia and European Pharmacopoeia specifications and is used as a food supplement ingredient.

9. Notes on Nomenclature and Scope

The term "dihydrogencitrate" is a chemical naming fragment that describes the dihydrogen citrate anion — i.e., the citrate ion retaining two of three of its ionizable protons. This anion appears in multiple supplement-relevant salt compounds beyond choline, including glucosamine dihydrogen citrate (PubChem CID 86615620, molecular formula C₁₂H₂₁NO₁₂), which is used as an alternative glucosamine salt form in joint-health supplements, and sodium dihydrogen citrate (sodium citrate monobasic, CAS 18996-35-5), which is used as a urinary alkalinizer and buffering agent. When the term "dihydrogencitrate" appears in a dietary supplement context without a named cation, it most commonly refers to choline dihydrogen citrate given its prominence in USP, BP, and EP monographs and its long history of use as a named pharmaceutical agent. Authors and formulators should specify the complete compound name to avoid ambiguity.