Norwegian scientists studying the health records of 43,000 men and women have shown that smoking less than five cigarettes daily triples the risk of dying of heart disease or lung cancer.

"In both sexes, smoking 1-4 cigarettes per day was associated with a significantly higher risk of dying from ischaemic heart disease and from all causes, and from lung cancer in women," said Dr Aage Tverdal of the Norwegian Institute of Public Health in Oslo.

The study was published in the journal Tobacco Control.

Men who were light smokers were about three times more likely to die of lung cancer than non-smokers.

In women the risk rose to five times higher.