Chalk up another one for the no-good-deed-goes-unpunished theory — a British study suggests that city dwellers who bicycle to make the air cleaner for everyone may be doing damage to their own lungs.


The study — presented last month at the European Respiratory Society’s Annual Congress in Amsterdam — showed that cyclists have higher levels of black carbon in their lungs than pedestrians. Researchers collected sputum samples from five London bicycle commuters and five pedestrians. The bicyclists had 2.3 times more black carbon in their lungs.


“This could be due to a number of factors, including the fact that cyclists breathe more deeply and at a quicker rate than pedestrians while in closer proximity to exhaust fumes,” said researcher Dr. Chinedu Nwokoro, an active cyclist.


Nwokoro said cyclists should consider traffic — and the attendant vehicle exhaust — when planning commuting routes.


Don’t park your bike forever, though.


A 2010 study by University of Utrecht in the Netherlands concluded that trading your car keys for a bicycle helmet would lengthen your life. While increased exposure to air pollution might reduce your lifespan up to 40 days and the increased odds of a traffic accident might take off another five to nine days, the benefits of increased exercise would add three to 14 months. A big net gain.


So, biking to work is still good for you — and for the rest of us.


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