Amino Acid
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L-Ornithine supports ammonia detoxification via the urea cycle, reducing exercise fatigue and supporting liver function. At 2-6 g/day, it may improve sleep quality, reduce perceived fatigue during prolonged exercise, and support recovery in hepatic encephalopathy.
L-Ornithine's role in the urea cycle is well-established biochemistry, but supplementation evidence is still emerging. The most robust clinical use is as LOLA for hepatic encephalopathy. For exercise and sleep, studies are promising but small. The sleep study showing improved quality with just 400 mg is notable for its low effective dose. More large-scale RCTs are needed to confirm exercise performance benefits.
L-Ornithine's role in the urea cycle is well-established biochemistry, but supplementation evidence is still emerging.
| Form | Bioavailability | Best For |
|---|---|---|
| L-Ornithine HCl | Moderate | General supplementation; most common form |
| L-Ornithine-L-Aspartate (LOLA) | Moderate | Liver support and hepatic encephalopathy treatment |
| Ornithine Alpha-Ketoglutarate (OKG) | Moderate | Wound healing and clinical nutrition applications |
General recommendation: 2-6 g daily, taken before bed or before exercise
Timing: Before bed for sleep; 60 min before exercise for fatigue; with meals for liver support
| Condition | Recommended Dose | Evidence |
|---|---|---|
| Exercise fatigue | 2-6 g before prolonged exercise | Preliminary |
| Sleep quality | 400 mg before bed | Preliminary |
| Hepatic encephalopathy (LOLA) | 9-18 g/day L-ornithine-L-aspartate | Strong |
Upper limit: Doses up to 12 g have been used acutely; GI side effects common above 6-8 g
Safety profile: Generally Safe
Preliminary evidence suggests yes. Ornithine accelerates ammonia clearance through the urea cycle, and ammonia accumulation contributes to central fatigue during prolonged exercise. A clinical trial found ornithine supplementation reduced perceived fatigue during extended cycling. Benefits are likely most relevant for endurance exercise lasting over 45 minutes, where ammonia buildup becomes significant.
A 2014 study in stressed Japanese workers found just 400 mg ornithine before bed improved subjective sleep quality and reduced morning cortisol levels. The mechanism may involve ammonia clearance (ammonia can disrupt sleep) and stress hormone modulation. Evidence is still limited to small studies, but the low dose and good tolerability make it worth trying.
Both participate in the urea cycle but at different steps. Arginine is primarily used to boost nitric oxide for blood flow and vasodilation. Ornithine is produced from arginine by arginase and drives the urea cycle forward for ammonia detoxification. They can be taken together for complementary urea cycle and NO support, though high ornithine doses divert arginine away from NO production.