RDNA retrospective cohort study of ~33,00 U.S. veterans, ~12,00 of whom were supplementing with nicotinamide, found that the supplement reduced the incidence of skin cancer by 14%, or by as much as 50% when supplementation started after a first skin cancer.
Summary: https://medicalxpress.com/news/2025-09-dietary-supplement-effective-skin-cancer.html
Original paper (not open access): https://jamanetwork.com/journals/jamadermatology/article-abstract/2838591
Dietary supplement found effective for skin cancer prevention
The dietary supplement nicotinamide has been recommended by dermatologists for people with a history of skin cancer since 2015, when a clinical study with 386 participants showed that those who took the vitamin B3 derivative developed fewer new occurrences.