Using data collected between 1997 and 2014, from the annual U.S. National Health Interview Survey, researchers examined the medical histories, lifestyle habits and demographics of smokers and nonsmokers. The study included 390,929 adults, ages 25 to 74 years (average age of 47), 56% female. Occasional smokers were excluded from the study. Current smokers were grouped by the age at which they began smoking.
During the follow-up period, 4,479 people died before the age of 75 from heart disease or stroke. After adjusting for potential confounding variables, such as age, education, alcohol consumption, region and race, researchers found:
58% were never smokers; 23% were ex-smokers; and 19% were current smokers;
Among current smokers, 2% had started smoking before age 10, and 19% began smoking between ages 10 and 14; and
Those who quit smoking by the age of 40 reduced their excess risk of premature death from cardiovascular disease by about 90%.