People who smoke fewer than five cigarettes a day too cause long-term damage to their lungs, according to a new research.
For the study published in The Lancet Respiratory Medicine, the researchers looked specifically at lung function--the amount of air a person can breathe in and out--in smokers, ex-smokers, and never-smokers.
Because of the large number of people in the study--more than 25,000-- researchers could see differences in lung function among light smokers (less than 5 cigarettes per day) and heavy smokers (more than 30 per day) that other studies have been unable to detect.
Their analysis found that lung function in light smokers declines at a rate much closer to that of heavy smokers, as compared to non-smokers.
This means that a light smoker could lose about the same amount of lung function in one year as a heavy smoker might lose in nine months.
The study also tested an assumption, based on a 40-year-old study, that the rate of decline in lung capacity "normalises" within a few years of quitting smoking.
According to the researchers, light smokers may have a greater risk of developing chronic obstructive pulmonary disease (COPD).
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