Researchers have found that smoking 20 cigarette sticks a day can cause 150 deadly changes to your lungs every year.  The study shows a direct link between the number of cigarettes smoked in an entire lifetime and the number of DNA mutations of cancerous tumors.

Smoking causes irreparable damages to multiple organs.  According to researchers, the highest mutation rates were seen in lung cancers, but other parts of the body, including throat, liver, and bladder, also had smoking-associated mutations.

Authors of the study said that a pack of cigarettes a day for a year can cause an average of 97 cell mutations 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.

One of the study's researchers, Ludmil Alexandrov of Los Alamos National Laboratory in the United States, said that it would now be difficult to explain how smoking increases cancer risks in body parts that don't come into direct contact with 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. The genome of every cancer provides a kind of archaeological record, written in the DNA code itself, of the exposures that caused the mutations.  Looking in the DNA of cancers can provide provocative new clues to how (they) develop and thus, potentially, how they can be prevented," Alexandrov said.

Eighty percent of all deaths from chronic obstructive pulmonary disease (COPD) are caused by smoking.  According to the World Health Organization, smoking kills about 6 million of the world's population every year.  About 5 million of those deaths are the result of direct tobacco use while more than 600, 000 are the result of non-smokers being exposed to second-hand smoke. If the trend continues, there will be a total of around 1 billion tobacco-related deaths this century.