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.

However, data to validate those findings in a larger study group has been lacking because nicotinamide can be purchased over the counter without being entered into patients’ medical records. In a new study published Sept. 17 in JAMA Dermatology, researchers found a way to get that data by analyzing records from the Veterans Affairs Corporate Data Warehouse.

Nicotinamide is on the VA’s official formulary, so the researchers checked the outcomes of 33,833 patients for their next skin cancer diagnosis following baseline treatment with 500 milligrams of nicotinamide twice daily for longer than 30 days. They looked for occurrences of basal cell carcinoma and cutaneous squamous cell carcinoma.