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Photo of site author, Shelly Albaum

Shelly Albaum

Editor, Science of NAD

Important Disclosures

1. This is my personal website

All opinions are my own. Nobody writes here but me.

2. Supplements Are Not Medicines

Health Supplements like nicotinamide riboside are not intended to cure or treat any disease, condition, or illness.

3. No Medical Advice

I am a lawyer and a journalist, not a doctor, and I offer no medical advice. But I do follow the science, and I can bring to your attention

some interesting studies. You can read more about me here. And check with your physician -- your physician can look at this research, too.

4. Commercial Affiliations

I am a ChromaDex shareholder, and a marketing affiliate for Amazon and Rakuten. As a result, I will sometimes mention or recommend products that I endorse, like Tru Niagen, which I take every day. I may earn a small commission from qualifying purchases if you were referred directly from this site and completed a purchase. [Thank you!] You can read more about our advertising, privacy, and data collection policies here

What are "Metabolic Pathways" and why do they matter for NAD?

Depending on where, when, and how the NAD will be biosynthesized, different precursors will be needed and different limits encountered...

Diagram -- Metabolic Pathways for NAD Biosynthesis: De Novo, Preiss-Handler, Brenner, and Salvage

The four main pathways for intracellular biosynthesis of NAD correspond to four different NAD precursors: Trp (De Novo Pathway), NA (Preiss-Handler Pathway), NAM (Salvage Pathway), and NR (Brenner Pathway).

The De Novo Pathway is not an important source of intracellular NAD because your body mostly uses tryptophan for protein synthesis instead of for NAD synthesis.

The Preiss-Handler Pathway for Niacin is poorly expressed in numerous cell types and is down-regulated by viral infection.

The Salvage Pathway for Nicotinamide is rate-limited under some circumstances (especially age and stress).

The Brenner Pathway is well-expressed in cells and can bypass rate-limiting steps in the other pathways that prevent the other pathways from adequately replenishing NAD. That is the reason NR gets so much attention. NMN might have its own pathways in some cell types, rather than first getting degraded to NR and NAM, but it's not clear yet.

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