What supplement best boosts nitric oxide?
L-citrulline (3-6g daily) is the most effective NO precursor, outperforming L-arginine due to better absorption. Beetroot juice (300-600mg nitrate) works through a separate pathway. L-arginine is mostly broken down before it can help.
- L-citrulline: best NO precursor (3-6g daily)
- Beetroot juice: 300-600mg nitrate, separate pathway
- L-arginine: 40% destroyed by liver, less effective
- Don't use mouthwash right before beetroot (kills conversion bacteria)
L-Citrulline: The Best Nitric Oxide Precursor
L-citrulline at 3-6g daily raises plasma arginine levels more effectively than taking L-arginine directly. This sounds backward, but it's well established. Citrulline bypasses first-pass liver metabolism, so more of it reaches your bloodstream intact.
Your kidneys convert citrulline to arginine, which then produces nitric oxide via the eNOS enzyme. The result: vasodilation, better blood flow, lower blood pressure, and improved exercise performance.
For exercise: 6-8g citrulline malate 30-60 minutes before training. Multiple meta-analyses show it increases reps to failure by 3-5 reps on average. Not huge, but consistent.
For blood pressure: 3-6g L-citrulline daily. A 2019 meta-analysis of 10 RCTs found systolic BP dropped by 4-6 mmHg. That's clinically meaningful.
Quick Tips
- →6-8g citrulline malate pre-workout (or 3-4g pure L-citrulline)
- →Raises arginine better than taking arginine directly
- →Blood pressure drops 4-6 mmHg systolic on average
Beetroot Juice and Nitrates
Concentrated beetroot juice providing 300-600mg dietary nitrate improves exercise endurance by 1-3% in trained athletes and more in recreational exercisers. The mechanism is different from citrulline. Dietary nitrate gets converted to nitrite by bacteria in your mouth, then to nitric oxide in your stomach and bloodstream.
This is why mouthwash can actually blunt the effect. Antibacterial mouthwash kills the oral bacteria you need for the nitrate-to-nitrite conversion. Weird but true.
Beetroot powder supplements are hit or miss. Many contain far less nitrate than actual concentrated beetroot juice. Look for products that list nitrate content in milligrams. If they don't list it, they probably don't contain enough.
L-Arginine: Why It Usually Disappoints
L-arginine is the direct precursor to nitric oxide. So logically, more arginine should mean more NO. In practice, it doesn't work that way for most people.
The problem: your liver breaks down about 40% of oral arginine before it reaches systemic circulation. Your intestines also express arginase, which further degrades it. By the time it hits your blood vessels, you've lost most of it.
Arginine does work for some specific conditions. Doses of 6-10g daily help some people with erectile dysfunction and peripheral artery disease. But for general exercise performance or blood flow, citrulline is the better choice. Every time.
Key Takeaways
Citrulline is the clear winner for nitric oxide support. Take 3-6g daily for blood flow, or 6-8g citrulline malate before exercise. Add beetroot juice (not powder) if you want the dietary nitrate pathway too. Skip L-arginine for general NO boosting.
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