Vitamin B3 is a water-soluble vitamin that has been found in things like bran, liver, and tuna fish. It is currently being studied as a way to prevent skin cancer. Vitamin B3 has been found to be preventative against skin cancer, according to Australian researchers.
One article (1) looked at vitamin B 3 and its ability to prevent skin cancer. They studied almost 400 individuals, who had a mean age of 66 years. Half of the participants took 500 mg of nicotinamide (vitamin B 3), while the other half took a placebo drug.
While the results of the research were promising, they recommended that further research be done on more humans with a high risk of skin cancer so they can say for sure that vitamin B3 could prevent skin cancer.
Source: 1.Skin Cancer Foundation Position: Nicotinamide (vitamin B3) could help prevent skin cancer. http://www.skincancer.org/media-and-press/press-release-2015/vitaminb3. Accessed 9/12/16.