NEW DELHI: Long-term smokers showed symptoms not fitting any of the existing tobacco-related disease criteria, in a study conducted in the US.

The study included participants who had smoked one pack of cigarettes a day for 20 years or more. 1379 people aged 40 to 80 years were recruited.

Half of them showed persistently high levels of respiratory symptoms such as shortness of breath, daily cough and phlegm, and decreased ability to exercise. However, they performed well in the breathing tests used to diagnose chronic obstructive pulmonary disease (COPD), researchers at the University of California-San Francisco (UCSF), US, found.