Nicotinamide mononucleotide (NMN) acts as a precursor to nicotinamide adenine dinucleotide (NAD+), enhancing its biosynthesis and subsequently activating key signaling pathways such as the insulin signaling pathway, which involves the phosphorylation of AKT and mTOR, thereby improving muscle insulin sensitivity and remodeling. NMN also influences mitochondrial metabolism and promotes mitophagy, potentially through the SIRT3 pathway, while its effects on natural killer (NK) cell function are linked to NAD+ salvage pathways that regulate mitochondrial homeostasis and cytokine production. The precise mechanisms underlying NMN's effects on various biological processes, particularly in immune modulation and aging, are still being elucidated.