数据之源，洞见之始

Nicotinamide riboside is involved in nicotinate and nicotinamide metabolism. Nicotinamide riboside was originally identified as a nutrient in milk. It is a useful compound for the elevation of NAD+ levels in humans. Nicotinamide riboside has recently been discovered to be an NAD(+) precursor that is converted into nicotinamide mononucleotide by specific nicotinamide riboside kinases, Nrk1 and Nrk2. It has been shown that exogenous nicotinamide riboside promotes Sir2-dependent repression of recombination, improves gene silencing, and extends the lifespan of certain animal models without calorie restriction (PMID: 17482543). Supplementation in mammalian cells and mouse tissues increases NAD(+) levels and activates SIRT1 and SIRT3, culminating in enhanced oxidative metabolism and protection against high-fat diet-induced metabolic abnormalities (PMID: 22682224). Recent data suggest that nicotinamide riboside may be the only vitamin precursor that supports neuronal NAD+ synthesis (PMID: 18429699). Nicotinamide riboside kinase has an essential role in the phosphorylation of nicotinamide riboside and the cancer drug tiazofurin (PMID: 15137942).