Smokers who quit increase their life expectancy and their quality of life - that was the message from doctors this week after it emerged that a leading anti-smoking campaigner has been diagnosed with lung cancer.
It was also stressed that Allen Carr, who set up clinics to help people to stop smoking in more than 30 countries after writing a best-selling book on the topic, was a very heavy smoker for more than 30 years and is now aged 73.
"He used to smoke 100 a day and only gave up when he was 50, so that's a lot of cigarettes over 30 years or more," said Dr Luke Clancy, chairman of anti-smoking group Ash.
Research indicates that only male smokers who stop before they reach 35 manage to keep their chances of developing lung cancer to a minimum.
Dr Clancy said that of the three main health risks associated with smoking - heart disease, lung cancer and chronic bronchitis - the lung cancer risk declines quite slowly after giving up.
A major UK study by Richard Doll reported in the British Medical Journal in 2004 found that smokers reduced their life expectancy by 10 years. Stopping at 30 allowed a person to regain these 10 years but stopping at 50 regained only five years, meaning they would die five years younger than if they had never smoked.
Dr Clancy said, however, that the participants in this study were male doctors, who were likely to have started smoking later than smokers generally. "There is evidence that females who smoke are more prone to lung cancer than males who smoke," he said.
People who start smoking as teenagers before their lungs are fully developed are also at greater risk.
The harsh reality for smokers is that they never regain the lung function they have lost so the key is to stop as early as possible to keep the damage to a minimum.
Some 2,000 people die from lung cancer each year in the Republic and practically all of these are caused by smoking. This is greater than the numbers who die from any other form of cancer. For example, fewer than 1,000 women die from breast cancer each year.
The benefits of quitting smoking are seen more quickly in the other two main illnesses associated with smoking. The risk of heart attack diminishes immediately and within two years is back to that of a non-smoker.
Dr Brian Maurer, medical director of the Irish Heart Foundation, said it was never too late to stop smoking: "If you quit after having a heart attack, the chances of getting another attack or of developing angina are much less."
Dr Maurer, who smoked heavily up to the age of 29, said that while genetic factors played a part in heart disease, smoking meant a person could start having problems in their 40s instead of their 70s. "If I had persisted in smoking, I would not be around now," he said.
For those who develop chronic bronchitis as a result of smoking - it ranks fourth in causes of death in the western world - the benefits of quitting are also felt immediately as the rate of decline in lung function becomes equal to a non-smoker, whereas it declines very rapidly in smokers, Dr Clancy said.
Apart from life expectancy, it is also pointed out that quality of life improves drastically after quitting. Breathing becomes easier within weeks and people are able to live a more active life.
Allen Carr, who turned his decision to quit into a very successful worldwide business, gave himself a few extra years of life but ultimately it appears that he smoked too many for too long to save himself from lung cancer.