Oral NMN Supplements Shield Skin from UV Aging in Mouse Study

UV-B radiation is the primary environmental driver of photoaging, degrading collagen, disrupting the skin barrier, triggering inflammation, and generating oxidative stress through MAPK pathway activation. Existing research on NMN's skin-protective effects has largely relied on intraperitoneal injections, limiting real-world applicability. This study addressed that gap by testing orally administered NMN in a well-established UV-B photoaging mouse model.

SKH-1 hairless female mice were divided into five groups: untreated vehicle, UV-B only, UV-B plus NMN 100 mg/kg/day, UV-B plus NMN 300 mg/kg/day, and UV-B plus collagen 300 mg/kg/day as a positive control. UV-B irradiation was delivered three times weekly for 10 weeks with escalating doses from 50 to 140 mJ/cm² (cumulative dose: 1,760 mJ/cm²). NMN or collagen was dissolved in PBS and administered orally once daily throughout the study. Outcomes spanned functional skin metrics (hydration, elasticity, TEWL, wrinkle topography), histology (H&E, Masson's trichrome), Western blot (MAPK phosphorylation), RT-qPCR (TNF-α, IL-6, MMP-1, HAS-1, HAS-2), and serum superoxide dismutase (SOD) activity.

Oral NMN produced statistically significant improvements across virtually every endpoint. Functionally, NMN-treated mice showed markedly reduced wrinkle depth, length, and area, along with improved hydration, skin elasticity, and TEWL restoration toward vehicle-control levels. Histologically, epidermal hypertrophy was attenuated and collagen fiber density was substantially preserved compared to the UV-B-only group. At the signaling level, NMN dose-dependently inhibited phosphorylation of ERK, JNK, and p38 — the three major MAPK branches driving MMP upregulation and inflammatory cascades. Downstream, TNF-α and IL-6 mRNA were reduced, and MMP-1 expression was suppressed, collectively indicating reduced ECM degradation pressure. HAS-1 and HAS-2 expression, which decline under UV-B stress and reduce hyaluronic acid synthesis, were restored by NMN treatment. Systemic antioxidant defense, measured by serum SOD activity, was also significantly enhanced in NMN-treated animals.

The 300 mg/kg dose consistently outperformed the 100 mg/kg dose and in many parameters rivaled or exceeded the collagen positive control, suggesting a dose-response relationship and potential superiority to conventional collagen supplementation for specific photoaging endpoints. These multi-layered effects — spanning oxidative stress, inflammatory signaling, ECM remodeling, and hyaluronic acid metabolism — position oral NMN as a broad-spectrum photoaging intervention rather than a single-mechanism agent.

Clinically, the oral delivery route is a meaningful advancement over prior injection-based NMN research, though important caveats remain. The study used only female mice, doses far exceed typical human NMN supplementation (250–1000 mg/day in adult humans versus scaled mouse equivalents), and all assessments were conducted in an animal model without human validation. Whether these benefits translate to human skin physiology, particularly through the oral bioavailability pathway, requires dedicated clinical trials.