At least a quarter of long-term smokers will develop the incurable lung condition chronic obstructive pulmonary disease (COPD), a study suggests.
The longer someone smokes the higher their risk, the study said
COPD describes a range of conditions, including bronchitis and emphysema, which make it difficult to breathe.
Over 8,000 people aged 30 to 60 were studied by UK and Danish researchers for 25 years in the Thorax study.
A spokesman for the British Lung Foundation said the study should act as a "wake-up call" to UK smokers.
It is estimated that 13.3% of Britons over 35 may have developed features
Between 600,000 and 900,000 people in the UK have been diagnosed with COPD
COPD is the sixth most common cause of death in England and Wales, killing more than 30,000 a year
Of the people studied, who all lived around Copenhagen, 5,280 were smokers, 1,513 had never smoked and 1,252 were ex-smokers.
At the end of the study, the researchers found that at least 25% of the smokers without any initial symptoms of the disease had "clinically significant" COPD, while up to 40% had some signs of the condition.
Over the 25 years, 2,900 people died, with 109 dying from COPD.
Nine out of 10 of those who died were smokers at the start of the study, while just two non-smokers died of the disease.
The risk of COPD was reduced in those who gave up smoking early on in the study - none of the ex-smokers developed severe COPD and only seven died.
At the end of the study, the lungs of almost all the male non-smokers continued to function well.
However, the same was true for only six out of 10 of those who continued smoking.
Around nine out of 10 female non-smokers had lungs that functioned well at the end of the study compared with only seven out of 10 female smokers.
Most smokers 'susceptible'
Writing in Thorax, the researchers who were led by Dr Peter Lange of Hvidovre Hospital, Hvidovre, Denmark, said: "Our main finding is quite simple - the longer people smoke, the higher the risk of developing COPD."
In an editorial in the journal, Dr Nick Anthonisen of the University of Manitoba in Canada, said: "The message is that many smokers develop airway obstruction if they live long enough and continue to smoke, and that the number that do so is increasing.
"An argument can be made therefore that many, perhaps most, smokers are 'susceptible' to COPD if they live long enough."
But he said there were long-term smokers who did not develop the condition, and more work was needed to find out why there was such a distinction.
Professor Stephen Spiro, from the British Lung Foundation, said: "This is an important study showing that people are even more at risk of COPD than we previously thought.
"It should act as a further wake-up call to smokers to get their lungs tested and to get help to stop.
"It's also a wake-up call to the UK - COPD is our fifth biggest killer, yet it's a hidden disease."