Scientists have found that smoking a pack a day of cigarettes can cause 150 damaging changes to a smoker's lung cells each year.
The findings come from a study of the devastating genetic damage, or mutations, caused by smoking in various organs in the body.
New research published on Thursday in the Journal Science, provides a direct link between the number of cigarettes smoked in a lifetime and the number of mutations in the DNA of cancerous tumours.
The study provides the first accurate measure of the devastating genetic damage smoking inflicts not only in the lungs, but also disrupting cell function in other organs of the body that are indirectly exposed to the smoke.
"Before now, we had a large body of epidemiological evidence linking smoking with cancer, but now we can actually observe and quantify the molecular changes in the DNA," said Ludmil Alexandrov of Los Alamos National Laboratory in the United States, one of those who carried out the research.
The results also showed that smoking a pack of cigarettes a day leads to an average of 97 mutations in each cell in the larynx, 39 mutations for the pharynx, 23 for the mouth, 18 for the bladder, and six mutations in every cell of the liver each year.
Previous studies proved that smoking contributes to at least 17 types of cancers, but until now it remained unclear exactly how cigarettes caused these tumours.
Researchers studied over 5,000 tumours comparing cancers from smokers with cancers from people who had never smoked.
Tobacco smoking claims the lives of at least 6 million people every year worldwide and if the trend continues, the World Health Organisation predicts more than a billion tobacco-related deaths in this century.
According to WHO, if you quit smoking today, these are the beneficial health changes that take place:
- 20 minutes - your heart rate and blood pressure drop.
- 12 hours - the carbon monoxide level in your blood drops to normal.
- 2-12 weeks - your circulation improves and your lung function increases.
- 1-9 months - coughing and shortness of breath decrease.
- 1 year - your risk of coronary heart disease is about half that of a smoker's.
- 5 years - your stroke risk is reduced to that of a nonsmoker 5 to 15 years after quitting.
- 10 years - your risk of lung cancer falls to about half that of a smoker and your risk of cancer of the mouth, throat, bladder, cervix, and pancreas decreases.
- 15 years - the risk of coronary heart disease is that of a nonsmoker's.