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STOCKHOLM (Reuters Health) – Smokers who quit and then start up again could have a greater and more rapid decline in lung function than smokers who never quit, according to study results presented at the 11th Annual European Respiratory Society Congress in Berlin last week.

This must not be interpreted to mean that smokers should abandon any attempts to quit, investigator Dr. Bo Lundbהck quickly added in his presentation.

On the contrary, "all smokers must try to stop smoking," said Dr. Lundbהck, an associate professor in respiratory medicine at the National Institute for Working Life in Stockholm. "If you succeed, then do not start up again."

As part of the Obstructive Lung Disease in Northern Sweden Studies, Dr. Lundbהck and colleagues reviewed data on 1116 Swedish people aged 35 to 68 at baseline, comparing forced expiratory volume at one second (FEV1) values at the beginning and end of a 10-year period. They also analyzed data collected from questionnaires about smoking habits during the 10-year interval.

This general population sample was divided into five groups: those who never smoked, those who had stopped smoking 10 years before the preliminary observation, those who stopped smoking during the 10-year study period, ex-smokers who re-started during the observation period, and those who smoked throughout. The study did not include smokers who "took breaks" for less than a year.

Nonsmokers showed the lowest mean annual decline in FEV1, at 25 mL, Dr. Lundbהck told Reuters Health. The researchers found that the mean annual decline was 40 mL for smokers who smoked during the whole 10-year study period. Ex-smokers who started smoking again after having quit for at least a year showed the greatest annual decline in lung function, at 40 to 50 mL.

"What ex-smokers lose in lung function, they'll never get back. The part of the lung they can use will be smaller," Dr. Lundbהck said. "And, within the first couple years after ex-smokers re-start [after having quit for at least a year], the decline was much greater."

It is still unclear for how many years this rapid decline in lung function continues and whether it stabilizes at the level of individuals who smoked continuously. Dr. Lundbהck and his fellow researchers are now analyzing that data.

They speculate that the reason for a rapid decline in lung function among ex-smokers who re-start could be that they have lost a defense in the lungs against smoke "pollution," a defense built up while they smoked to protect against the "constant attack" on the lungs. When people stop smoking the source of pollution ceases and perhaps so does the defense, Dr. Lundbהck said, leaving the lungs more vulnerable.