"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.

The researchers tracked the health and death records and smoking habits of the men and women, who had been screened for heart disease at the start of the study, from the 1970s to the 2002.

They found very little difference in the risk of dying from cancer, apart from lung cancer. 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.

The dangers of smoking are well documented. Previous research has shown that smokers die on average 10 years earlier than non-smokers but stopping, even in middle age, can halve the risk.

It is also a risk factor for heart disease and stroke and raises the odds of developing age-related macular degeneration which is the leading cause of blindness in the elderly.

Tverdal and his colleague Dr Kjell Bjartveit, of the National Health Screening Service in Oslo and a co-author of the study, said health officials must emphasize more strongly that light smokers are also endangering their health.

.