The team analyzed nearly 8,000 people aged 30 to 60 for a period of twenty-five years. About 5,280 of those analyzed were smokers, 1,513 had never smoked and 1,252 were ex-smokers.
The experts found that at least 25 percent of the smokers who had no symptoms of the disease at the beginning of the study developed "clinically significant" COPD. About 40 percent developed signs of the condition.
Before the study was completed, 2,900 people died. Up to 109 of those who died were killed by COPD. About nine of 10 of those who died were smokers at the start of the study. The team reported just two non-smokers died from COPD.
At the end of the study, Dr Peter Lange of Hvidovre Hospital, Hvidovre, Denmark, wrote in the Thorax journal, "Our main finding is quite simple - the longer people smoke, the higher the risk of developing COPD."
The lungs of most of the men who were non-smokers among the group were still functioning properly after the study. Among the smokers, the ratio was lower. Just 6 out of 10 smokers' lungs still functioned well after the study.
