Refueling the Repair Crew: Nicotinamide, NAD+, and the DNA Damage Sunlight Leaves Behind

Key Takeaways:

• Ultraviolet light welds adjacent bases in DNA into cyclobutane pyrimidine dimers, and clearing them requires nucleotide excision repair — an ATP-hungry process that ultraviolet exposure itself sabotages by collapsing the cell’s NAD+ supply.
• In the ONTRAC phase 3 trial, 386 patients who had already had at least two nonmelanoma skin cancers took 500 mg of nicotinamide twice daily for 12 months, and the rate of new keratinocyte cancers fell by 23 percent versus placebo (95% CI 4–38, P=0.02).
• Nicotinamide is not niacin — it does not cause flushing and does not move lipids — and it is not nicotinamide riboside or NMN; the skin-cancer evidence belongs to plain nicotinamide only.

Every hour spent in July sunlight leaves a molecular paper trail, which is exactly why UV Safety Month is a reasonable time to talk about nicotinamide and DNA repair. Ultraviolet photons are absorbed directly by DNA, and the classic injury is a covalent weld between two adjacent pyrimidine bases: the cyclobutane pyrimidine dimer. A skin cell cannot ignore that lesion. It must excise the damaged stretch and resynthesize it through nucleotide excision repair, a multi-enzyme operation that runs on ATP. The cruel design flaw is that ultraviolet radiation simultaneously activates PARP enzymes, which consume NAD+ to flag the damage, and that consumption drives NAD+ and ATP down at the precise moment the repair machinery needs them most. The result is a cell with a full work order and an empty fuel tank — a distinct problem from the collagen breakdown and pigment changes covered in the molecular story of photoaging, and one that sunscreen alone does not address from the inside.

Nicotinamide is the amide form of vitamin B3 and a direct precursor to NAD+, and this is where it earns its place. In human keratinocytes and in ex vivo human skin, nicotinamide prevented the ultraviolet-induced fall in cellular energy, increased both the proportion of cells performing excision repair and the repair rate within each cell, and measurably reduced cyclobutane pyrimidine dimer burden. It also blunts a second consequence of sunlight: ultraviolet radiation suppresses cutaneous immune surveillance, the same surveillance that culls abnormal keratinocytes before they become tumors. In a randomized, double-blinded crossover study using the Mantoux model, oral nicotinamide at 500 or 1500 mg daily significantly reduced ultraviolet-induced immunosuppression in healthy volunteers without altering immunity in unirradiated skin. Two mechanisms, one molecule, and both point the same direction.

Can nicotinamide and DNA repair actually lower skin cancer risk?

In high-risk patients, the answer is yes — and the honest boundaries of that answer matter. The Australian ONTRAC trial randomized 386 people who had each already had at least two nonmelanoma skin cancers in the prior five years to 500 mg of nicotinamide twice daily or placebo, and at 12 months the rate of new keratinocyte cancers was 23 percent lower in the nicotinamide arm. That is a real, inexpensive, over-the-counter benefit for a defined population. It is also a benefit that has not been demonstrated in low-risk people who have never had a skin cancer, and a follow-up trial in organ-transplant recipients on immunosuppression found no reduction at all — the effect does not simply generalize. Two clarifications prevent most of the confusion in conversations about prevention: nicotinamide is not niacin, so there is no flushing and no lipid effect, and it is not nicotinamide riboside or NMN, the fashionable longevity precursors that were never the molecule tested. If the trial data are what you are after, the trial used nicotinamide — and it does not replace shade, clothing, or sunscreen, which remain the first line.

References:

1. Chen, A. C., Martin, A. J., Choy, B., Fernández-Peñas, P., Dalziell, R. A., McKenzie, C. A., et al. (2015). A phase 3 randomized trial of nicotinamide for skin-cancer chemoprevention. New England Journal of Medicine, 373(17), 1618-1626.
2. Surjana, D., Halliday, G. M., & Damian, D. L. (2013). Nicotinamide enhances repair of ultraviolet radiation-induced DNA damage in human keratinocytes and ex vivo skin. Carcinogenesis, 34(5), 1144-1149.
3. Yiasemides, E., Sivapirabu, G., Halliday, G. M., Park, J., & Damian, D. L. (2009). Oral nicotinamide protects against ultraviolet radiation-induced immunosuppression in humans. Carcinogenesis, 30(1), 101-105.
4. Allen, N. C., Martin, A. J., Snaidr, V. A., Eggins, R., Chong, A. H., Fernandéz-Peñas, P., et al. (2023). Nicotinamide for skin-cancer chemoprevention in transplant recipients. New England Journal of Medicine, 388(9), 804-812.