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How to test

By around 40, most adults make roughly half the nitric oxide they did at 20. Nitric oxide supports circulation, blood pressure, stamina and recovery.
Rocket, spinach, beetroot
Leafy greens and beetroot are rich in dietary nitrates. The free Nitric Oxide Kitchen guide has 7 days of recipes.
Nasal breathing
Humming and nasal breathing release nitric oxide in the sinuses. Try the free daily practice on our site.

Support both pathways
L-citrulline plus beetroot and arugula nitrates, protected by antioxidants. Retest in two to four weeks.
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They give a practical snapshot of salivary nitrite, a marker of nitric oxide status. Testing at the same time each morning gives the most consistent picture.
It suggests your nitric oxide status could be better supported through diet, lifestyle or supplementation. It's not a diagnosis.
See the pack details above. Most people test two to three times a week when they start.
Orders are dispatched the next business day. Most arrive within 3 to 7 business days, and you'll get a tracking link by email.
Once you've ordered, log in to your account to read The Butterworth Protocols as a flipbook or download the PDF. The Nitric Oxide Kitchen eating guide is emailed to you.