We have all seen urban runners, skating and bicyclists dodging traffic or paralleling busy roads and highways, and wondered: do the benefits of being in shape outweigh the dangers of breathing all that polluted air? According to medical experts, the answer may well be no.

Dr. Ronald Crystal, chief of pulmonary and critical care medicine at New York-Presbyterian Hospital/Weill Cornell Medical Center, says that the main dangers of city air are ozone, fine particulate matter, and carbon monoxide, he says. These pollutants irritate the lungs and respiratory system, and can exacerbate asthma, bronchitis, emphysema or cardiopulmonary disease.

What is a dedicated runner to do? If it is summer and you have heart or lung disease, Dr. Crystal says, you should exercise indoors, preferably in an air-conditioned room. If you have to go outdoors, do it in the early morning or evening, when the air is cooler and ozone levels are at their lowest.

Epidemiologic studies have linked rises in air pollutants to harmful effects on the heart and lungs, increased emergency hospital admissions — even rises in the death rate.

Pollutants cause inflammation or irritation of the airway lining, according to Dr. Crystal. More mucus and phlegm is then produced and the muscles surrounding the airway respond by contracting. This makes it harder to breathe.

Carbon monoxide comes from cigarette smoke and automobile exhaust. It has a tremendous ability to force oxygen out of our circulatory system. Overexposure may cause headache, dizziness, confusion and dangerous increases in body temperature.

Ozone is also related to car exhaust. It causes a person working out to have difficulty taking deep breaths and makes exercise more stressful and difficult.

Dr. Crystal offers these simple tips:
  • Do not run on or near roads where there is heavy truck or bus traffic.
  • Work out in the early morning or later in the evening.
  • Exercise indoors if possible.
  • If you experience any difficulty breathing, stop immediately and see your doctor.