It's never too late to stop smoking for adults who are diagnosed with chronic obstructive pulmonary disease and also smoke, a U.S. health official says. Dr. Anne Wheaton, an epidemiologist at the Centers for Disease Control and Prevention in Atlanta, said patients with COPD might experience constant coughing, excessive phlegm and shortness of breath during normal activities. Smoking is the most common cause of COPD, but air pollutants and respiratory problems also put people at risk. "The most important thing is not to smoke. But if you are a smoker, smoking cessation -- quitting smoking -- is very important," Wheaton said in a statement. "Also, you can reduce exposure to air pollutants such as secondhand smoke. And people who are exposed to dust, chemicals, or fumes at work should always use the proper protective equipment."