Quitting smoking is the "single most important step" smokers can take to extend their lives, and those who stop before age 50 cut by half the risk of dying in the next 15 years of their lives, Surgeon General Antonia Novello reported Tuesday.

In her first report on smoking since taking over the post from vocal tobacco foe C. Everett Koop in March, Novello emphasized the "good news" about the health benefits of stopping smoking rather than scaring Americans with the "bad news" of smoking-related diseases and death.About 38 million Americans have kicked the habit - about half of all living adults who ever smoked. However, another 50 million Americans still smoke, and an estimated 390,000 people die each year from diseases caused by smoking.

"Smoking cessation has major and immediate health benefits for men and women of all ages. People who quit smoking live longer than those who continue to smoke," Novello said in her 628-page report.

People who stop smoking before age 50 have just half the risk of dying in the next 15 years compared with continuing smokers, the report said. Even older smokers can reap benefits, with the risk of death falling about 10 percent over the 15 years for an otherwise healthy man who quits smoking between the ages of 60 and 64.

Stopping smoking increases life expectancy because it reduces the risk of smoking-related disorders like lung cancer, coronary heart disease and stroke, as well as ulcers and other potentially fatal lung and artery diseases.

After quitting smoking, people gain only about 5 pounds on average and less than 4 percent gain more than 20 pounds, the report said. Kicking the habit can also cause anxiety, irritability, frustration, anger and other signs of increased stress in many people.