Summary of Ornithine
Primary Information, Benefits, Effects, and Important Facts
L-Ornithine is a nonprotein amino acid (not used to create proteins) that is an intermediate of the urea cycle, and provision of ornithine to a cell is actually the rate limiting step of the cycle. Ornithine binds with a molecule known as carbamoyl phosphate which requires ammonia to be produced and then is converted into L-Citrulline giving off urea as a byproduct. Due to this, the conversion is one that reduces ammonia concentrations in the blood and concomitantly increases urea.
L-Ornithine is thought to be important for conditions that are characterized by an excess level of ammonia, and this is mainly focused on either hepatic encephalopathy (clinical liver condition) or prolonged cardiovascular exercise. A reduction in serum ammonia has been repeatedly found in persons with hepatic encephalopathy (most studies use infusions, although it appears to apply to high dose oral supplements as well) while there are only two studies assessing exercise; the one that was better suited to assess the influence of ammonia (using prolonged exercise rather than acute exercise) did find an anti-fatigue effect.
Furthermore, reductions in self-reported fatigue have been noted in persons with hepatic encephalopathy and in persons subject to a hangover (the process of getting drunk off of alcohol will increase serum ammonia) when ornithine is taken before drinking, but only in persons sensitive to alcohol perhaps.
There is currently one study using ornithine paired with arginine that noted improvements in lean mass and power output in weightlifters, but this is an old study that has not been replicated and its practical relevance is uncertain.
Finally, the increases in growth hormone seen with ornithine are similar to those seen with arginine. Technically they exist, but as they are very short lived and the body seems to compensate the overall increaes in whole-day growth hormone are not significant. Since the main properties of growth hormone being concerned with (increased lean mass gain and fat loss) are more related to day-long exposure rather than short-bursts, it is unlikely that ornithine has a role here.
In the end, ornithine looks somewhat promising for reducing ammonia concentrations in the blood and thus enhancing performance of prolonged exercise (45 minutes or more) which is in part due to it being elevated in the blood for a few hours after ingestion despite exercise.
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How to TakeMedical Disclaimer
Recommended dosage, active amounts, other details
Ornithine supplementation (as hydrochloride) is taken in the range of 2-6g daily. Most studies use a dose in this range, but despite serum levels being somewhat dose dependent there is a chance of intestinal distress at doses above 10g.
Most studies use Ornithine hydrochloride (Ornithine HCl) which appears to be effective. Ornithine HCl is 78% Ornithine by weight, and so for the 2-6g range an equivalent dose for L-Ornithine L-Aspartate (50% Ornithine) would be 3.12-9.36g and an equivalent dose for L-Ornithine α-ketoglutarate (47% Ornithine) would be 3.3-10g. These two forms are theoretically more effective, but lack sufficient comparative testing.
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Human Effect Matrix
The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects ornithine has on your body, and how strong these effects are.
|Grade||Level of Evidence [show legend]|
|Robust research conducted with repeated double-blind clinical trials|
|Multiple studies where at least two are double-blind and placebo controlled|
|Single double-blind study or multiple cohort studies|
|Uncontrolled or observational studies only|
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
|-||High See all 3 studies|
|- See 2 studies|
|- See study|
|Minor||Very High See 2 studies|
|Minor||- See study|
|Minor||Moderate See 2 studies|
|-||- See study|
|-||- See study|
|-||- See study|
|-||- See study|
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Things to Note
Arginine is known to cause diarrhea at doses of 10g or higher, and since Ornithine shares the same intestinal transporters (diarrhea occurs when the transporter gets saturated) it is possible that supplemental ornithine can reduce the amount of arginine requires to induce diarrhea
Ornithine itself in high doses can induce diarrhea (10-20g), but is likely a lesser concern than is arginine
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