Scientists showed that women who quit smoking have a 21% lower risk of dying from heart disease within five years of quenching their last cigarette. People who quit smoking also can decrease the risk of dying from other conditions, because when smokers kick the smoking they become healthier.

Stacey Kenfield, a postdoctoral research fellow in the department of epidemiology at the Harvard School of Public Health in Boston, said: "It's never too early to stop, and it's never too late to stop."

In the United States smoking is still the leading preventable cause of death. Scientists have found that smoking causes not only lung cancer but also heart diseases, and other cancers and respiratory diseases.

According to the World Health Organization, an estimated 3 million people in industrialized countries will have died as a result of tobacco use by 2030, and an additional 7 million people in developing countries face the same fate.

Current smokers had almost tripled the risk of overall death compared with women who had never smoked.

Researchers added that women who started smoking earlier in life were at a higher risk for overall mortality, of dying from respiratory disease and from any smoking-related disease. However, a smoker's overall risk of dying returned to the level of a never-smoker 20 years after quitting.

For chronic obstructive pulmonary disease, the return to normal took almost 20 years, although there was an 18% reduction in the risk of death seen within five to 10 years after quitting. And the risk for lung cancer didn't return to normal for 30 years after quitting, although there was a 21% reduction in risk within the first five years compared with women who continued to smoke.

Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, said: "When I tell people to quit smoking, I say the effect of the heart precedes that of the lungs. If you've smoked, you need to be aware that you're still at an increased risk of lung cancer."

It’s never too late to quit and there's never an easy time to do it.

But in order to quit, smokers need to break their addiction to nicotine and to the habit of smoking - which also includes the pleasure that they get from smoking.