Smoking only a few cigarettes a day almost triples the risk of heart disease and lung cancer, researchers said today.

The impact of light smoking - between one and four cigarettes a day - is even stronger in women, according to the study published in journal Tobacco Control.

People who smoked between one and five cigarettes a day were almost three times more likely to die from coronary artery disease than those who had never smoked.

The research was carried out by Dr Aage Tverdal, from the Norwegian institute of public health, and Dr Kjell Bjartveit, from the national health screening service in Oslo.

They tracked the health and death rates among almost 43,000 men and women in Norway from the mid 1970s up until 2002.

At the start of the study all those taking part were aged 35 to 49 and were screened for cardiovascular disease and diabetes.

Taking into account other risk factors, the researchers were able to conclude that light smoking did significantly endanger health.

Men who were light smokers were almost three times more likely to be killed by lung cancer, while women were almost five times as likely to die of the disease as their non-smoking peers.

The researchers also found that light smokers had significantly higher death rates from all causes - up by 1.5 times - compared with people who had never smoked.

The researchers concluded: "In men and women smoking one to four cigarettes per day, there was a distinct increase in risk of death from ischaemic heart disease and from all causes.

"For ischaemic heart disease, the steepest increase was in both sexes between zero and one to four cigarettes per day.

"Above this level, the slope was less pronounced."

The researchers said that many people in the past had assumed that a few cigarettes a day were not harmful to health. But they said their research had now shown that this was not the case.

"The results from this and other studies imply that smoking control policymakers and health educators should emphasise more strongly that light smokers are also endangering their health," the researchers said.

June Davison, medical spokesman for the British Heart Foundation, said: "Smoking kills over 30,000 people each year in the UK from heart and circulatory disease.

"This study only adds fuel to the evidence that every cigarette counts."

She added: "Cigarette smoke can affect the lining the arteries, leading to a build-up of a fatty plaque called atheroma. This can cause potentially fatal conditions such as a heart attack or a stroke."

Meanwhile, a new treatment for lung cancer that significantly increases the chances of a patient surviving more than a year is available from today.

Tarceva, which is taken orally as a simple white pill, targets a molecule with a key role in the growth and extended lifespan of cancer cells.

The European Medicines Agency has now granted a Europe-wide licence for the drug to be used to treat non-small cell lung cancer in patients who have failed on at least one prior chemotherapy treatment.

But those waiting for treatment on the NHS might not get the drug as quickly.

It is thought that Tarceva, which is made by drugs giant Roche, will not be reviewed by the National Institute for Health and Clinical Excellence until 2007.