The raised risk of cancer in people using insulin decreases over time, a large study showed, Novo Nordisk, the world's biggest maker of insulin, said on Thursday.

Novo-owned Steno Diabetes Center said the biggest-ever registry linkage study on the effect of insulin duration or diabetes duration on cancer incidence confirmed a link between diabetes and cancer.

This increased incidence was especially evident in the first years after diagnosis but decreased over time, Steno said in a statement.

The increased risk of cancer was most pronounced in people using insulin, and the study showed that for these patients the risk was highest at the start of insulin treatment and decreased over time.

Steno presented the study at the European Association for the Study of Diabetes' annual meeting in Stockholm on Thursday.

Contrary to what was previously thought, the risk of cancer does not increase with longer use of insulin, said Daniel Witte, head of Steno's epidemiological group.

The fact that the increased cancer risk decreases the longer the patient has diabetes strongly indicates that diabetes does not cause cancer in itself, Steno said.

Furthermore, the marked drop in risk with long-term insulin use indicate that other factors than insulin may play an important role.

The study followed the entire Danish population, currently 5.million people, over 13 years.