People who quit smoking cigarettes before age 40 may lessen their chances of premature death from cardiovascular disease by 90 percent, according to a report in the Journal of the American Heart Association. Based on tracking of 390,929 adults for about 17 years, researchers also found that, overall, smokers were three times more likely than nonsmokers to die of heart disease or stroke. At highest risk were those who had started smoking before age 15. In the United States, nearly 5 million teens and 40 million adults smoke, according to the Centers for Disease Control and Prevention. The CDC describes cigarette smoking as the country’s “leading cause of preventable disease, disability and death,” saying it accounts for about 1 in 5 deaths every year. Inhaled cigarette smoke, which contains a multitude of chemicals, interferes with a range of body processes, such as causing blood pressure to rise and the heart to beat faster, reducing blood flow from the heart and restricting the flow of oxygen needed by body tissues. Besides cardiovascular disease, smoking has been shown to increase risk for, or cause, such health issues as lung cancer, emphysema, chronic obstructive pulmonary disease, chronic bronchitis, diabetes, tuberculosis, immune system problems, some eye diseases and more. The researchers found that, for cardiovascular disease, the earlier a person quit smoking, the more their risk of premature death declined. But the American Cancer Society says that “quitting at any age can give back years of life that would be lost by continuing to smoke.”