Non-smokers will still always have healthier lungs than smokers, the study said. / Getty

The study of 50,000 people showed that "good genes" protect some heavy smokers from the effects of their nicotine habit

The mystery of why some people are able to smoke heavily without developing a lung condition has been explained by scientists.

Mutations in DNA enhance lung function in some people and protect them against the often deadly impact of smoking, according to the Medical Research Council.

The study looked at why some smokers never develop lung disease while others - despite never taking a drag on a cigarette - still develop life-threatening lung conditions. Researchers surveyed 50,000 people, all volunteers for the UK's Biobank project.

The study focussed on Chronic Obstructive Pulmonary Disease, but not heart disease or cancer, which also increase with smoking.

In particular they looked at Chronic Obstructive Pulmonary Disease (COPD), which is thought to affect three million people in the UK - many of whom dismiss it as "the smoker's cough" according to the NHS. 

Researchers discovered sections of our DNA that reduces the risk of COPD, meaning some people were at lower risk of developing lung disease.

But those same genes do not necessarily protect against heart disease and cancers, which were not looked at in the study. Yet the current findings could present new opportunities for drug development, experts told the BBC.

Professor Martin Tobin, one of the researchers at the University of Leicester, said the results gave "fantastic news clues about how the body works that we really had little idea about before, and it's those things that are likely to lead to some really exciting breakthroughs for drug development."

The most important thing people could do to reduce their chances of smoking-related diseases like cancer and heart disease was to stop smoking, he told the BBC.

Ian Jarrold, the head of research at the British Lung Foundation, said the findings could also give insights for non-smokers.

"Understanding genetic predisposition is essential in not only helping us develop new treatments for people with lung disease, but also in teaching otherwise healthy people how to better take care of their lungs," he told the BBC.