Nicotinamide Riboside (NR)New

A form of vitamin B3 and a direct precursor to NAD+ (nicotinamide adenine dinucleotide), sold under brand names such as Niagen. NR is chemically distinct from NMN (nicotinamide mononucleotide), which Peak Human also tracks separately — both raise NAD+ but via different transport and conversion steps, and head-to-head human comparisons remain limited. NR has one of the larger human clinical trial bases among NAD+ precursors, consistently raising blood NAD+ levels, though translation into measurable functional or cognitive benefit has been inconsistent. EVIDENCE UPDATE (September 20, 2026): Peer-reviewed. Nature Metabolism 2026;8:1282-1290 (Tretowicz, Scantlebery, Schomakers et al.; Houtkooper lab, Amsterdam UMC) measured NAD+ across seven independent human cohorts with a rigorously validated UHPLC-high-resolution mass spectrometry method built to account for real-world analytical variability, and found whole-blood NAD+ remarkably STABLE with chronological age and UNCHANGED by lifestyle interventions - while rising, as expected, with nicotinamide riboside supplementation. NR itself was the precursor used to confirm the assay responds. The authors conclude that blood NAD+ is not a useful biomarker of ageing or lifestyle, and that much of the previously reported age-related decline may reflect assay variability rather than biology. This does not refute tissue or intracellular NAD+ decline, does not alter NR's well-replicated ability to raise circulating NAD+, and does not change the (largely null) functional-endpoint picture summarised above. It does mean a blood NAD+ level should not be used to establish that a patient "needs" NR, nor a post-supplement rise presented as evidence of benefit - that rise is a pharmacokinetic confirmation of absorption. Counterweight: GeroScience 2026 (Itabashi Longitudinal Study on Aging, 16 Sept 2026) found lower median whole-blood NAD+ among the 32 of 529 community-dwelling Japanese adults aged 65+ (6.0%) who met revised J-CHS frailty criteria, robust to adjustment and sensitivity analyses. That is the clearest human link yet between circulating NAD+ and a functional phenotype, but it is cross-sectional with a small frail subgroup, reverse causation is unaddressed, and no supplement was tested.