The study found shisha smokers had 40-70 ppm of CO in their breath - affecting 8-12% of their blood.
Dr Hilary Wareing, director of the Tobacco Control Collaborating Centre, told the BBC's Asian Network she was shocked by the results of the research.
"Our mouths opened at the level of harm - none of the tests we did showed anything other than shisha is hazardous to health."
Paul Hooper, regional manager at the Department of Health, said the findings made the dangers of shisha a "major issue".
He said many people regard shisha "as not even smoking".