Research on niacin and NAM

• Supplementation of nicotinic acid and its derivatives up-regulates cellular NAD+ level rather than nicotinamide derivatives in cultured normal human epidermal keratinocytes

  In cultured skin cells, nicotinic acid supplementation 1.3-fold up-regulated intracellular NAD+ level significantly and its metabolites nicotinic acid mono nucleotide also increased NAD+ level by 1.5-fold with 100 μM application. Surprisingly, NAM and its derivatives could not up-regulate cellular NAD+ levels in keratinocytes.

• Bacterial PncA improves diet-induced NAFLD in mice by enabling the transition from nicotinamide to nicotinic acid

  Gut bacteria play an important role in NAD production. NAD boosting effect of oral NAM (nicotinamide) NR (nicotinamide riboside) is largely dependent on gut bacteria breaking them down to nicotinic acid, and that nicotinic acid being processed via Preiss Handler pathway. Nicotinic acid highly efficient at boosting NAD in mammals.

• Bacteria Boost Mammalian Host NAD Metabolism by Engaging the Deamidated Biosynthesis Pathway

  This research used stable isotope tracing and microbiota-depleted mice to reveal that salvage NAD+ precursor supplements like nicotinamide (NAM) and nicotinamide ribose (NMR) don't actually boost NAD+, but depend on bacteria to first convert them into nicotinic acid. And that the resulting nicotinic acid is the converts to NAD+ via the Preiss Handler pathway.