A drug called metformin prescribed for diabetes reduces the risk of a group of blood cancers, medical researchers said on Friday in a study that has bolstered evidence for its anti-cancer effects.

The researchers in Denmark have found that people who used metformin were at significantly lower risk of developing myeloproliferative neoplasms (MPNs), a disorder in which the bone marrow makes too many red blood cells, certain white blood cells, or platelets.

Their study has also noted what the researchers call a dose-response relationship — the longer the duration that people used metformin, the lower their risk of developing MPNs. The findings were published on Friday in the journal Blood Advances published by the American Society of Hematology.

“We were surprised by the magnitude (strength) of the association we saw in the data,” Daniel T. Kristensen, a researcher at Aalborg University Hospital in Denmark and the study’s lead author, said in a media release. “We saw the strongest effect in people who had taken metformin for more than five years compared to those who had taken the treatment for less than a year.”

MPN is an umbrella term that includes chronic myelogenous leukaemia and several other rare cancers that involve red blood cells, platelets or certain types of white blood cells called eosinophils and neutrophils. The disorders may cause anaemia, infections, bleeding problems and fatigue, among other symptoms.

Researchers compared metformin use among patients diagnosed with MPNs with people from the general population between 2010 and 2018. Among 3,816 MPN patients in the sample, 268 with MPN had taken metformin compared to 1,573 (8.2 per cent) of 19,080 in the general population.