A common vitamin B3 supplement, niacin, slowed glioblastoma growth in mice, a new study reports. The effect worked through the immune system, not the tumour directly.Glioblastoma is the most common malignant brain tumour in adults, killing more than 10,000 Americans a year. Standard treatment has barely changed in decades, and survival gains are rare.Researchers fed mice doses equal to about 250 to 500 mg of niacin per day for humans, doses long used for cholesterol.

The vitamin shifted immune cells around tumours into a state that attacked cancer.The study is published in Cell Reports Medicine. It found that niacin and drugs that mimic it triggered strong immune responses and extended survival in the animals.The authors warn against self-medicating. The work needs human trials, and niacin’s effect depends on the tumour’s immune environment.

A simple B3 pill is not a proven brain-cancer therapy. The team stressed the vitamin did not kill tumour cells directly. Instead it reprogrammed immune cells to mount a stronger anti-cancer response.