Changes in ultraviolet B radiation-induced DNA damage and erythema after oral nicotinamide and polypodium leucotomos in healthy volunteers: an intraindividual controlled trial

Background: Skin cancer, primarily caused by ultraviolet radiation (UVR), is the most common malignancy worldwide. The increasing incidence emphasizes the need for new protective measures. Objective: To evaluate the photoprotective effects of oral nicotinamide (NAM) and polypodium leucotomos (PL) in healthy individuals. Methods: In this intraindividual controlled trial, participants (skin phototype I-III) were treated orally with NAM (2000 mg daily) or PL (480 mg daily) for 30 days. Protective effects against narrowband UVB-induced erythema and DNA damage were assessed by measuring the minimal erythema dose (MED) and thymidine dimer (TT-dimers) levels in urine and skin before and after treatment. Results: A total of 47 participants completed the study. PL treatment increased MED by 29% (p = 0.00018), while NAM did not affect MED (p = 0.533). Neither treatment significantly affected TT-dimer levels measured in skin biopsies or urine. Limitations: Non-randomized design and use of a narrow-band light source not covering the full solar UV spectrum. Conclusion: PL reduced UVB-induced erythema but had no measurable effect on DNA damage. NAM did not provide protection against erythema or DNA damage. Further research should explore the discrepancy between these findings and chemopreventative effects on skin cancer, using a light source covering the full solar UV spectrum.