The team of researchers, led by Jenny Hallberg, of the Department of Public Health Sciences at Karolinska Institutet in Stockholm, studied more than 40,000 Swedish twins for finding out to what extent does behaviour, environment and genes each play a role in the development of chronic bronchitis.

'Smoking behavior has a known genetic component and smoking is a primary risk factor for chronic bronchitis,' Hallberg said.

It was found that around 40 percent of the risk for chronic bronchitis was due to hereditability, and at the same time, 14 percent of the genetic risk was also linked to a genetic inclination to smoke, irrespective of whether the individual actually smoked or not. The researchers also discovered that chronic bronchitis in addition to emphysema, account for the majority of the cases of chronic obstructive pulmonary disease, or COPD.

For the study, the researchers assessed data from the Screening Across Lifespan Twin (SALT) study in Sweden, which surveyed all known living twins in Sweden born in 1958 or earlier.

In the survey, the researchers asked questions on zygosity, whether the twins shared 100 or 50 percent of their genetic material, smoking history and a checklist of common diseases. The questions were designed in order to find out whether the interviewee had chronic bronchitis or not.