Smoking damages your DNA, a new study has found - and the damage is visible even in smokers who have quit for 30 years.

It is still worth giving up - most of the damage heals within five years, but some does remain, the researchers say.

Smoking leaves a ‘footprint’ on people’s genes through DNA methylation - altering 7,000 genes which can lead to the development of smoking-related illness.

‘Our study has found compelling evidence that smoking has a long-lasting impact on our molecular machinery, an impact that can last more than 30 years,’ said Roby Joehanes of Harvard Medical School in Boston.

‘The encouraging news is that once you stop smoking, the majority of DNA methylation signals return to never smoker levels after five years, which means your body is trying to heal itself of the harmful impacts of tobacco smoking.’

Study author Dr Stephanie London said: ‘These results are important because methylation, as one of the mechanisms of the regulation of gene expression, affects what genes are turned on, which has implications for the development of smoking-related diseases.

‘Equally important is our finding that even after someone stops smoking, we still see the effects of smoking on their DNA’