A study by scientists in Finland has found that mobile phone radiation can cause changes in human cells that might affect the brain, the leader of the research team said on Wednesday.

But Darius Leszczynski, who headed the two-year study and will present findings next week at a conference in Quebec, said more research was needed to determine the seriousness of the changes and their impact on the brain or the body.

The study at Finland’s Radiation and Nuclear Safety Authority (STUK) found that exposure to radiation from mobile phones can cause increased activity in hundreds of proteins in human cells grown in a laboratory, he said.