In the largest study ever into the possible connection between cancer and cell phones, researchers at the Institute of Cancer Epidemiology in Copenhagen found no evidence that cell phone usage can cause cancer.

The study examined cancer registry and cell phone subscriber records for 358,403 Danes at least 30 years of age from 1990 to 2007. Researchers found no higher incidence of brain tumors or other forms of cancer in the study cohorts.

“Our study provides little evidence for a casual association, but we cannot rule out a small to moderate increase in risk for subgroups of heavy users,” said Patrizia Frei, a study author, in a statement.

A June study from the International Agency for Research on Cancer, of the World Health Organization, found that mobile phones could cause brain cancer. The Food and Drug Administration and the Federal Communications Commission have found no causal link between cell phone usage and cancer.