Ex-smokers,
light smokers not exempt from lung damage
Columbia University
Irving Medical Center
People who smoke fewer
than five cigarettes a day cause long-term damage to their lungs, according to
a new study led by researchers at Columbia University Vagelos College of
Physicians and Surgeons.
"Many people
assume that smoking a few cigarettes a day isn't so bad," says study
leader Elizabeth Oelsner, MD, a Herbert Irving Assistant Professor of Medicine
at Columbia University Vagelos College of Physicians and Surgeons. "But it
turns out that the difference in loss of lung function between someone who
smokes five cigarettes a day versus two packs a day is relatively small."
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. Lung function declines
naturally with age (starting in one's 20s), and it's well-known that smoking accelerates
the decline.
Because of the large
number of people in the study -- more than 25,000 -- Oelsner and her colleagues
could see differences in lung function among light smokers (<5
cigarettes/day) and heavy smokers (>30) 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 than non-smokers. [Compared to the rate of decline in a
never-smoker, set to zero for the analysis, the additional decline for light
smokers is 7.65 mL/year and 11.24 mL/year for heavy smokers].
That 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.
"Smoking a few cigarettes a day is much riskier than a lot of people think," Oelsner says. "Everyone should be strongly encouraged to quit smoking, no matter how many cigarettes per day they are using."
After Quitting, Lungs
Don't Fully Recover
The study also tested
an assumption, based on a 40-year-old study, that the rate of decline in lung
capacity "normalizes" within a few years of quitting smoking.
The new study shows
that although lung capacity declines at a much lower rate in ex-smokers (an
extra 1.57 mL/year compared with nonsmokers) than current smokers (an extra
9.42 mL/year), the rate doesn't normalize (reach zero) for at least 30 years.
"That's
consistent with a lot of biological studies," Oelsner says. "There
are anatomic differences in the lung that persist for years after smokers quit
and gene activity also remains altered."
Light Smokers and COPD
Smoking's effect on
lung function explains why smokers are more likely to develop chronic
obstructive pulmonary disease (COPD), which is diagnosed when lung function
dips below a certain threshold.
Light smokers may have
a greater risk of developing COPD than most researchers have realized, Oelsner
says. Most COPD studies have looked only at smokers with heavier habits (>10
pack years).
"We probably need
to expand our notions of who is at risk," Oelsner says. "In the
future, if we find therapies that reduce the risk of developing COPD, everyone
at increased risk should benefit."