The study found that the use of these drugs appeared to triple the risk of cancer of the colon - part of the large bowel - and the researchers claim that there is evidence that the drugs have a direct toxic effect.
The incidence of colon cancer in Denmark since the 1940s has increased by about 40 per cent and over the same period the use of anti-hypertensive drugs and sedatives has become widespread, the researchers said, writing in the Scandinavian Journal of Gastroenterology. About 10 per cent of the population are receiving drug treatment for blood pressure.
The study followed a group of 5,249 men, aged 40 to 59, over 18 years. They had been recruited initially to take part in a heart study. Colon cancer was diagnosed in 51 men and rectal cancer in 42 of them.
The drugs appeared to be a 'strong risk factor' for colon cancer, but more research was needed to prove a causal link, the researchers said.
Dr Richard Gray, a senior research fellow at the Imperial Cancer Research Fund's cancer studies unit in Oxford, said that the benefits of blood pressure treatment outweighed potential risks. 'The number of cancers in the study was small,' he said.