Orotic acid

Orotic Acid

1. Identity and Chemical Characterization

Orotic acid (systematic name: 2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid; also called uracil-6-carboxylic acid) is a naturally occurring pyrimidine derivative. It is classified chemically as a pyrimidinedione and a carboxylic acid. Its molecular formula is C₅H₄N₂O₄, and it carries the CAS Registry Number 65-86-1. It is a main intermediate in the pyrimidine nucleotide biosynthesis system, derived from dihydroorotic acid by means of dihydroorotic acid dehydrogenase, and is converted to orotidylic acid by means of orotic acid phosphoribosyltransferase (PRPP).

Historically, orotic acid was believed to be part of the vitamin B complex and was called vitamin B13, but it is now known that it is not a vitamin. It is not classified as an essential nutrient; humans synthesize it endogenously as part of the normal de novo pyrimidine pathway.

Orotic acid was first identified and isolated in the context of biological metabolite research in 1905, underscoring its significance in metabolic pathways related to nucleotide biosynthesis. It was isolated from cow's milk approximately 75 years before that Springer volume's publication date, by Biscaro and Belloni in Italy.

1.1 Natural Occurrence and Dietary Sources

Orotic acid is a normal part of the diet, being found in milk and dairy products, and it is converted to uridine for use in the pyrimidine salvage pathway predominantly in liver, kidney, and erythrocytes. Bovine milk, the main source of orotic acid in the human diet, contains approximately 80 ng orotic acid per milliliter, constituting about 0.1% of the fat-free solids. Orotic acid is virtually the only component in the acid-soluble nucleotide fraction of bovine milk. More precise HPLC-based measurements have confirmed these levels: average amounts in cow's milk were 69 to 74 mg/L, and orotic acid in milk was stable to heating but decreased during commercial yogurt fermentation.

Orotic acid content varies considerably among dairy products. The orotic acid content (mmol/L) in commercial milk products has been reported as follows: skim milk — 0.783; evaporated milk — 0.538; cream (12% fat) — 0.367; buttermilk — 0.449; yogurt — 0.331; kefir — 0.341; sour milk (2% fat) — 0.360; dried skim milk — 1.042. Orotic acid occurs in cow's milk but at higher levels in goat's and sheep's milk and has been found at levels of 15–118 mg/L in infant formula.

Variation is considerable in the concentration of orotic acid from dairy cows. This is primarily attributable to cow-to-cow variation. Stage of lactation is a secondary factor; orotic acid is low in colostrum, increases for 10 weeks, and remains constant through most of the rest of lactation; upon cessation of milking, orotic acid in lacteal secretions decreases within 6 weeks to the low content of colostrum.

1.2 Common Supplement Forms and Preparations

As a supplement ingredient, orotic acid is available in several forms:

• Free orotic acid — available as a standalone powder or in capsules.
• Mineral orotate salts — orotic acid is sometimes used as a mineral carrier in dietary supplements to increase bioavailability, most commonly for lithium orotate. The EFSA scientific panel assessed the safety and bioavailability of magnesium orotate, zinc orotate, calcium orotate, chromium orotate, copper orotate, iron orotate, manganese orotate, potassium orotate, sodium orotate, and choline orotate in food supplements.
• Magnesium orotate (magnerot) — a pharmaceutical-grade product used in several European countries under the trade name Magnerot, studied specifically in cardiovascular contexts.
• Lithium orotate — typically supplied in tablet or capsule form, most commonly 131 mg of the salt containing 5 mg elemental lithium.

Various orotate complexes — including calcium diorotate — were presented in the early 1970s as a superior means of mineral delivery by German physician Hans Nieper, who proposed that orotates cross biological membranes and enter cells more readily than traditionally employed salt formulations. Proponents of orotate salts argue that orotates do not dissociate at physiological pH and thus exist in sera as electrically neutral compounds. This is perhaps best evidenced by magnesium orotate dihydrate, which is poorly soluble in water and is known not to bind gastric acid; in contrast to more easily dissociable magnesium salts, magnesium orotate dihydrate does not exhibit a laxative effect following oral administration.

2. Endogenous Biosynthesis and Biochemical Role

2.1 De Novo Pyrimidine Synthesis Pathway

Orotic acid is the key substance in the biosynthesis of probably all naturally occurring pyrimidines. It is well-known as a precursor in biosynthesis of pyrimidines; in mammals it is released from the mitochondrial dihydroorotate dehydrogenase (DHODH) for conversion to UMP by the cytoplasmic UMP synthase enzyme.

The biochemical pathway proceeds as follows: ammonia and carbon dioxide combine in the presence of adenosine triphosphate to give carbamoyl dihydrogen phosphate, which reacts enzymatically with L-aspartic acid to yield ureidosuccinic acid, in enzymic equilibria with dihydroorotic acid. Subsequent oxidation by dihydroorotate dehydrogenase gives orotic acid. Orotic acid is then converted to orotidylic acid by orotic acid phosphoribosyltransferase (PRPP); the orotidylic acid is further rapidly converted to uridine monophosphate (UMP), and pyrimidine nucleotides such as uridine triphosphate (UTP) and cytidine triphosphate (CTP) are then synthesized.

Orotic acid is the precursor of pyrimidine nucleotides involved in many biochemical reactions: UTP and CTP serve as substrates for RNA polymerase, while UDP sugars serve as substrates for carbohydrate-containing macromolecules such as glycogen, glycoproteins, and glycolipids.

Synthesis is initiated by the formation of carbamoyl phosphate (CP) in the cytoplasm, with ammonia derived from glutamine. Orotic acid synthesis is abnormally high with hereditary deficiencies of urea-cycle enzymes or uridine monophosphate synthase. It is also elevated by ammonia intoxication and during feeding of diets high in protein, high in lysine with respect to arginine, or deficient in arginine, ornithine, and citrulline.

2.2 Pyrimidine Salvage and Uridine Release

Orotic acid is a naturally occurring substance and a key intermediate in the biosynthetic pathway of pyrimidines. Beyond the de novo pathway, orotic acid may improve myocardial purine and pyrimidine levels by stimulating hepatic release of uridine into the bloodstream, which in turn augments depleted myocardial pyrimidines and purines — a mechanism demonstrated in rat hearts. This hepatic conversion and subsequent uridine release into circulation represents a separate, downstream mechanism through which supplemental orotic acid could influence peripheral tissue nucleotide pools.

3. Historical and Traditional Use

Orotic acid does not have a documented tradition of use as an isolated compound in any pre-modern pharmacopoeial or ethnobotanical tradition. Its use as a supplement emerged from 20th-century nutritional and biochemical research rather than from historical folk medicine. Key historical milestones include:

• 1905: Orotic acid was first identified and isolated in the context of biological metabolite research.
• Early-to-mid 20th century: Early research into nutrition identified orotate as "vitamin B13," and its use as a complex with organic cations or metal ions was promulgated in bodybuilding and in assisting therapies of metabolic syndromes.
• 1950s–1970s (Italy and Europe): Italian scientists described the growth-promoting activity of orotic acid in vitamin B-deficient animals. In the last two decades of the 20th century, increasing interest in orotic acid came from several studies showing protective, therapeutic, or beneficial effects in different kinds of organ injuries, including various forms of hepatic insufficiency, myocardial infarction, and encephalopathy.
• 1970s (Germany): Orotic acid complexes — including calcium diorotate and magnesium orotate — were presented in the early 1970s as a superior means of mineral delivery by Hans Nieper, who proposed that orotates cross biological membranes and enter cells more readily than traditional salt formulations. Magnesium orotate subsequently became a prescription-adjacent product (sold under the name Magnerot) in Germany and several Eastern European countries for cardiovascular and magnesium-deficiency indications.
• 1970s–1980s (bodybuilding subculture): The use of orotic acid as a complex with organic cations or metal ions was promulgated in bodybuilding. It was marketed in this context based on its theoretical role in glycogen synthesis and energy metabolism.

4. Key Constituents and Active Compounds

Orotic acid is itself the pharmacologically relevant molecule in its supplemental forms. When used as a mineral carrier (e.g., magnesium orotate), the effects observed in studies may reflect the combined or independent contributions of both the mineral cation and the orotate anion. The key mechanisms proposed or established are:

4.1 Pyrimidine Precursor Function

The most firmly established biochemical role is orotic acid's function as an obligate intermediate in pyrimidine nucleotide synthesis. Orotic acid is ultimately responsible for the formation of UDP-glucose, an extremely high-energy compound that donates glycosyl units to the glycogen chain and is the immediate precursor to glycogen synthesis. UTP also possesses ergogenic potential due to its role in glycogen synthesis and its ability to donate phosphates for the formation of ATP and ADP; UTP hydrolysis is energetically equivalent to ATP hydrolysis.

4.2 Uric Acid Transport Competition

It has been established that the amelioration of gout by dairy products arises from the competition of orotate and urate at the hURAT1 transporter. The URAT1 transporter is primarily expressed on the luminal side of the renal proximal tubule, where it uptakes urate in exchange for exporting monocarboxylates, serving as a specific and major regulator of uric acid reabsorption from the urine. Orotic acid's structural similarity to urate allows it to compete for this transporter, potentially promoting urate excretion.

4.3 Myocardial Nucleotide Replenishment

Previous investigations in the heart suggest that orotate can protect recently infarcted hearts against further ischemic stress and may be beneficial in certain types of experimental cardiomyopathy. Studies indicate that orotic acid and its magnesium salt have a modest beneficial effect on the myocardium under conditions of stress ranging from myocardial infarction to severe physical exercise. The proposed mechanism is improvement of the energy status of the recently infarcted myocardium via nucleotide replenishment.

4.4 Hepatic Lipid Metabolism (Species-Specific Effect)

A well-characterized experimental mechanism — though of uncertain relevance at dietary doses in humans — involves orotic acid's effects on hepatic fat metabolism. Research has investigated the role of the AMPK–SREBP-1 pathway in OA-induced fatty liver; treatment with OA suppressed the phosphorylation of AMPK via proteasomal degradation of upstream kinase LKB1 and induced activation of SREBP-1 in both human hepatoma cell lines and primary rat hepatocytes. More specifically, in vivo experiments with rats reveal that the mechanisms by which an OA-supplemented diet induces fatty liver include enhanced de novo lipogenesis via the activation of SREBP-1c; the OA-induced SREBP-1c activity occurs via serine/threonine kinase 11 degradation, AMPK inhibition, and subsequent mTOR activation.

The activity and mRNA level of fatty acid synthase were obviously upregulated by orotic acid treatment, whereas the activities and mRNA concentrations of carnitine palmitoyl transferase and microsomal triacylglycerol transfer protein were significantly depressed. These combined effects — enhanced fat synthesis plus impaired export — are responsible for the hepatic lipid accumulation observed in rats. Critically, orotic acid has failed to induce fatty liver in other rodents, chicken, rabbits, pigs, or monkeys, indicating that OA-mediated hepatic steatosis could be restricted to one or a few species.

5. Scientific Evidence by Area of Use

5.1 Cardiovascular Disease and Heart Failure

The most clinically investigated application of an orotic acid preparation in humans involves magnesium orotate in the context of heart failure and arrhythmia. The landmark human trial was the MACH (Magnesium Orotate in Severe Congestive Heart Failure) study. The aim was to evaluate adjuvant magnesium orotate on mortality and clinical symptoms in patients with severe heart failure under optimal cardiovascular medication. In this monocentric, controlled, double-blind study, 79 patients with severe congestive heart failure (NYHA class IV) under optimal medical cardiovascular treatment were randomized to receive either magnesium orotate (6,000 mg for 1 month, then 3,000 mg for approximately 11 months; n=40) or placebo (n=39). After a mean treatment duration of 1 year, the survival rate was 75.7% compared to 51.6% under placebo (p<0.05). Clinical symptoms improved in 38.5% of patients under magnesium orotate, whereas they deteriorated in 56.3% of patients under placebo (p<0.001).

Based on these results, the investigators concluded that magnesium orotate may be used as adjuvant therapy in patients on optimal treatment for severe congestive heart failure, increasing survival rate and improving clinical symptoms and quality of life.

A subsequent meta-analysis examined the broader cardiovascular evidence base. The aim was to conduct a meta-analysis of clinical trials of magnerot (magnesium orotate) used in cardiac patients. The meta-analysis incorporated data from 19 randomized studies, including a total of 603 patients in the treatment group (receiving magnerot) and 587 in the control group (placebo). The authors concluded that the use of magnesium orotate is promising not only in treating mitral valve prolapse (MVP) and compensating for hypomagnesemia, but also in preventing and treating cardiac arrhythmias, regulating blood pressure, and improving the function of the autonomic nervous system.

Evidence strength: The MACH trial had notable limitations: it was monocentric, relatively small (n=79), conducted by a single research group, and the relative contribution of magnesium per se versus the orotate moiety to the observed effects cannot be determined from the study design. Most of the human data come from magnesium orotate, so it is difficult to separate the specific effects of orotic acid from those of the mineral itself. The overall quality of evidence remains low to moderate; independent large-scale replication has not been published.

5.2 Gout and Hyperuricemia

The proposed mechanism by which dairy intake lowers serum uric acid — and thereby potentially mitigates gout — involves orotic acid as one active constituent competing with urate at the renal URAT1 transporter. It has been established that the amelioration of gout by dairy products arises from the competition of orotate and urate at the hURAT1 transporter. URAT1 is primarily expressed on the luminal side of the renal proximal tubule, uptaking urate in exchange for exporting monocarboxylates; approximately 90% of the urate filtered from glomeruli is reabsorbed back to the bloodstream, while only 10% is excreted in the urine.

Evidence strength: This mechanism has been established biochemically and supported by evidence from observational studies linking dairy intake to reduced gout risk. However, isolated orotic acid supplementation as a specific uricosuric intervention has not been tested in dedicated human clinical trials. The evidence is mechanistic and observational in nature. It has been reported that orotic acid has a blood uric acid level-reducing action in patent literature, but robust controlled clinical trial evidence for this specific application is not available in the peer-reviewed literature.

5.3 Hereditary Orotic Aciduria (Diagnostic and Therapeutic Context)

Orotic acid plays a central role in the diagnosis and pathophysiology of a rare inborn error of metabolism. Orotic aciduria type I (OA1), also known as hereditary orotic aciduria, is a condition characterized by elevated levels of orotic acid in the urine. It typically becomes apparent in the first months of life with megaloblastic anemia, as well as delays in physical and intellectual development. OA1 is caused by changes in the UMPS gene; inheritance is autosomal recessive.

Hereditary orotic aciduria (HOA) is a rare inborn error of pyrimidine metabolism with autosomal recessive inheritance. It is the only known enzyme deficiency of the pyrimidine biosynthetic pathway, resulting from a deficiency in one or both of the activities of the bifunctional enzyme uridine-5-monophosphate synthase (UMPS) encoded by the UMPS gene. Orotic aciduria is a rare disease; fewer than 30 cases in human history have been reported in the literature.

Uridine monophosphate synthase deficiency, due to biallelic mutations in UMPS, is a rare condition presenting with megaloblastic anemia in the first months of life. If not treated with the pyrimidine precursor uridine, neutropenia, failure to thrive, growth retardation, developmental delay, and intellectual disability may ensue. In a documented case, the patient was started on uridine triacetate, after which she showed clinical, hematologic, and biochemical improvement.

The orotic aciduria that arises in children with defective UMP synthase can be rescued by oral uridine therapy, since UMP is the end-product and also a feedback inhibitor of the de novo pathway. This represents a therapeutic application of uridine (the downstream metabolite of orotic acid), not of orotic acid itself, which accumulates pathologically in these patients.

Additionally, elevated urinary orotic acid can also be seen in mitochondrial disorders, lysinuric protein intolerance, liver disease, and has been reported in Rett syndrome, malignancies, as a side effect of certain medications, and in trauma victims.

5.4 Athletic Performance and Ergogenics

Orotic acid has been marketed for athletic performance based on its theoretical role in glycogen synthesis. Orotic acid is ultimately responsible for the formation of UDP-glucose, which donates glycosyl units to the glycogen chain and is the immediate precursor to glycogen synthesis. UTP also possesses ergogenic benefits due to its role in glycogen synthesis and its ability to donate phosphates for the formation of ATP and ADP. It has also been reported in patent literature that orotic acid has an endurance-enhancing action and an action of decreasing oxygen consumption and energy consumption.

Evidence strength: The ergogenic evidence for orotic acid supplementation in humans is essentially absent from the peer-reviewed clinical literature. The proposed mechanisms are biologically plausible but have not been tested in adequately powered, controlled human trials. Claims in this area largely derive from theoretical extrapolation and historical marketing.

5.5 Hepatic Function

Increasing research in the latter decades of the 20th century showed protective, therapeutic, or beneficial effects of orotic acid in different kinds of organ injuries, including various forms of hepatic insufficiency. In Europe, orotic acid preparations have historically been used for liver conditions such as jaundice-type liver disease and general liver dysfunction.

However, the experimental literature presents a paradox: at high doses in rats, orotic acid is a well-characterized inducer of hepatic steatosis. Orotic acid has been intensively utilized to induce fatty liver in rats; FASN activity, TAG accumulation, decreased mitochondrial β-oxidation, and decreased secretion of VLDL and low-density lipoproteins (LDL) were identified as the main events promoting fatty liver due to OA exposure.

Evidence strength: Experimental evidence for orotic acid's hepatoprotective effects in humans is limited and mostly preclinical or from early, low-quality trials. The liver-damaging effects observed in rodents are a research concern, though they are species-specific (discussed in the Safety section below). Robust, modern, placebo-controlled human trials specifically examining hepatoprotective effects of orotic acid have not been published.

5.6 Urea Cycle Disorders (Secondary Orotic Aciduria)

Orotic acid measurement serves as a key diagnostic biomarker in secondary metabolic contexts. Orotic acid synthesis is abnormally high with hereditary deficiencies of urea-cycle enzymes or uridine monophosphate synthase. It is also elevated by ammonia intoxication and during feeding of diets high in protein, high in lysine with respect to arginine, or deficient in arginine, ornithine, and citrulline. Elevated urinary orotic acid is a clinical indicator of ornithine transcarbamylase (OTC) deficiency, one of the most common urea cycle disorders, because excess carbamoyl phosphate from the disrupted urea cycle is shunted into the pyrimidine pathway and exits as orotic acid.

6. Body Systems and Health Areas

Orotic acid has documented or proposed associations with the following body systems:

• Cardiovascular system: Via magnesium orotate, studied in heart failure, arrhythmia, mitral valve prolapse, and blood pressure regulation. Previous investigations in the heart suggest that orotate can protect recently infarcted hearts against further ischemic stress and may be beneficial in certain types of experimental cardiomyopathy.
• Renal/urinary system: Involvement in uric acid reabsorption at the URAT1 transporter; abnormal accumulation causes crystalluria in hereditary orotic aciduria. Hereditary orotic aciduria is an extremely rare, autosomal recessive disease caused by deficiency of uridine monophosphate synthase; untreated, affected individuals may develop refractory megaloblastic anemia, neurodevelopmental disabilities, and crystalluria.
• Hematopoietic system: Pyrimidine nucleotides are required for DNA synthesis in rapidly proliferating blood cells. Deficiency states (hereditary orotic aciduria) produce megaloblastic anemia. Orotic aciduria is characterized by excessive excretion of orotic acid in urine; it causes megaloblastic anemia and may be associated with mental and physical developmental delays.
• Immune system: In documented hereditary orotic aciduria cases, recurrent severe infections including disseminated varicella occurred during the first year of life, with an impression of immunodeficiency.
• Hepatic system: Orotic acid is metabolized predominantly by the liver. At high experimental doses, it disrupts hepatic lipid metabolism in rats; at physiological and supplemental levels, its hepatic effects in humans are under-characterized.
• Musculoskeletal/energy metabolism: Theoretical ergogenic role through UDP-glucose and glycogen synthesis pathways.
• Nervous system: Beneficial effects have been reported in encephalopathy and memorization processes in preclinical and early-stage investigations, though high-quality human evidence is absent.

7. Dosage Forms and Doses Reported in Studies

The following dosages are those specifically reported in the cited scientific literature and clinical trials:

• Magnesium orotate in severe heart failure (MACH trial): 79 patients with severe congestive heart failure (NYHA IV) were randomized to receive either magnesium orotate (6,000 mg for 1 month, then 3,000 mg for approximately 11 months) or placebo.
• EFSA-assessed proposed maximum daily intake: The proposed maximum intake level for magnesium orotate dihydrate in food supplements was 6,100 mg per day by adults, corresponding to around 5,000 mg/day orotic acid and 400 mg/day magnesium.
• Orotic acid equivalent corresponding to UL for magnesium supplementation: The proposed use level of 900 to 3,811 mg/day magnesium orotate dihydrate was equivalent to the upper tolerable limit of 250 mg Mg/day and to a maximum daily exposure to orotate of 3,192 mg.
• Human safety observation: Humans consuming 6 g of orotic acid daily have not shown adverse effects in the observation cited in early literature, though this finding predates modern regulatory standards.
• Lithium orotate supplementation: Lithium orotate is typically supplied in tablet or capsule form, most commonly 131 mg of the salt containing 5 mg elemental lithium.
• Rat fatty-liver induction model dose: Rats have been divided into groups and fed an AIN-93 diet with 1% orotic acid or without orotic acid for 10 days in hepatic steatosis research — a dose not relevant to human supplementation but cited to characterize the dose-dependency of hepatic effects.

8. Safety Considerations

8.1 EFSA Safety Assessment and Regulatory Standing

In 2009, the EFSA ANS Panel assessed the safety of orotic acid salts as sources of minerals added for nutritional purposes to food supplements. The conclusions were materially cautionary:

The Panel concluded that "in the light of the tumour-promoting effect of orotic acid in animal experimentation, the small margin of safety to this effect from foreseeable exposure, and the absence of any relevant studies on genotoxicity and of any developmental studies, the use of orotate … at the proposed levels of use is of safety concern."

The ANS Panel derived a no-observed adverse effect level (NOAEL) for orotic acid of 50 mg/kg body weight per day. The margin between the derived NOAEL for orotic acid and the exposure resulting from the proposed maximum use level is 0.7 (based on the average body weight of an adult person of 70 kg), which is even lower than the margin considered by the ANS Panel to be inadequate.

In the absence of clear data on toxicological safety and bioavailability, EFSA concluded that magnesium orotate dihydrate cannot be considered safe for human consumption under the proposed conditions of use.

8.2 Hepatic Steatosis Risk: Species Specificity

Orotic acid has been intensively utilized to induce fatty liver in rats; FASN activity, TAG accumulation, decreased mitochondrial β-oxidation, and decreased secretion of VLDL and LDL were identified as the main events promoting fatty liver due to OA exposure. However, the risk to humans is qualified by species specificity: orotic acid at 1% in the diet leads to severely fatty livers in rats; more than 0.1% is necessary to induce the effect. Rats appear to be unique in their susceptibility to fatty livers induced by orotic acid. Mice, guinea pigs, hamsters, chicks, dogs, pigs, and monkeys do not respond similarly to diets with 1% orotic acid.

Although the capacity of OA to cause steatosis is species-specific, previous in vitro studies indicate that humans could also be susceptible to OA-induced fatty liver. The EFSA Panel noted concerns raised regarding the exposure to orotic acid, based on several animal studies demonstrating tumour-promoting effects.

8.3 Tumour-Promoting Effects in Animal Models

Rats fed 1% orotic acid or arginine-deficient diets also showed more and larger foci positive for gamma-glutamyl transpeptidase and more liver tumours after administration of carcinogens and partial hepatectomy. Orotic acid feeding was also associated with the tendency for development of larger mammary tumours induced by chemical carcinogens in rats and with development of urinary bladder calculi containing high concentrations of orotic acid in mice. The safety assessment was based on a series of studies showing that orotic acid has a promoting and enhancing effect on tumour formation by various known tumour initiators. These data are from animal models and do not establish carcinogenicity in humans, but they underlie the EFSA regulatory concern.

8.4 B-Vitamin Interactions

Although the concentrations of vitamin B1, pantothenic acid, folate, and biotin in liver and blood were decreased by orotic acid-induced fatty liver, these urinary excretion amounts showed a specific pattern toward increase in rats. This suggests that high-dose orotic acid may perturb B-vitamin distribution — specifically through its effects on hepatic lipid metabolism — though this has been studied only in the context of the rat fatty liver model.

8.5 Lithium Orotate Safety

Despite early success marked by clinical efficacy in humans and an increase in brain lithium levels relative to Li₂CO₃ demonstrated in animal studies, research into lithium orotate was effectively curtailed following concerns regarding potential renal toxicity in 1979. A subsequent case report described: one published case report described the consequences of ingesting 18 tablets of lithium orotate, each containing 3.83 mg of elemental lithium. The subject described minor adverse effects typical of a standard dose of lithium (nausea with one episode of vomiting, mild tremor without rigidity, and normal vital signs), all of which resolved within 3 hours. The serum lithium concentration never exceeded 0.4 mmol/L, a level that would be expected following consumption of a comparable amount of elemental lithium from lithium carbonate in pharmaceutical form.

8.6 Nitrogen and Protein Metabolism Interaction

Orotic acid synthesis is abnormally high with hereditary deficiencies of urea-cycle enzymes. It is also elevated by ammonia intoxication and during feeding of diets high in protein, or deficient in arginine, ornithine, and citrulline. This means that conditions impairing urea cycle function may be confounded by elevated endogenous orotic acid, and supplemental orotic acid in such individuals warrants careful scrutiny.

8.7 Known Data Gaps

Human data at typical supplement doses have not shown clear liver toxicity, but long-term, high-dose safety studies are lacking. The absence of genotoxicity studies and developmental toxicity studies in humans was specifically noted by EFSA as a basis for its safety concerns. Another key issue is the bioavailability of magnesium from magnesium orotate dihydrate. EFSA noted that no comparative assessment was conducted between this synthetic form and natural sources of magnesium. Therefore, no scientific evidence is available to support the effectiveness of this compound's absorption in the human body.

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