If nothing else, this should worry smokers: the radiation dose from radium and polonium found naturally in tobacco can be a thousand times more than that from the caesium-137 taken up by the leaves from the Chernobyl nuclear accident.

Constantin Papastefanou from the Aristotle University of Thessaloniki in Greece measured radioactivity in tobacco leaves from across the country and calculated the average radiation dose that would be received by people smoking 30 cigarettes a day. He found that the dose from natural radionuclides was 251 microsieverts a year, compared with 0.199 from Chernobyl fallout in the leaves (Radiation Protection Dosimetry, vol 123, p 68).

Though the radiation dose from smoking was only 10 per cent of the average dose anyone receives from all natural sources, Papastefanou argues that it is an increased risk. “Many scientists believe that cancer deaths among smokers are due to the radioactive content of tobacco leaves and not to nicotine and tar,” he says.