This human clinical study examined how nicotinamide mononucleotide (NMN) affects gene expression and biological responses in skin fibroblasts, with the goal of understanding potential longevity-related effects on skin. The researchers identified distinctive gene expression profiles in fibroblasts exposed to NMN and characterized the resulting biological responses that may be relevant to skin aging processes. This is human clinical-level evidence investigating NMN’s direct molecular effects on skin cells involved in collagen and structural protein production.