If not controlled, later in life it will become a major risk factor for coronary heart disease, which leads to heart attack. Among young men and women — who are otherwise at very low risk of developing coronary heart disease —cigarette smoking may cause as many as 75 percent of the cases of coronary heart disease. The longer a person smokes, the higher the risk of coronary heart disease. More than 80,000 people die each year from coronary heart diseases caused by smoking.

Most adult smokers started when they were preteens or teenagers; smoking habits in youth seem to determine lifetime cigarette consumption. There’s also evidence that those who begin smoking before they’re 20 have the highest incidence and earliest onset of coronary heart disease and high blood pressure. Autopsy studies of smokers have raised questions about the effects of smoking in childhood and adolescence on the development of fatty buildups in arteries in adulthood.

What about passive or secondhand smoking?About 59 percent of American children ages 4–11 are exposed to secondhand smoke at home. Studies have shown that children (especially infants) of parents who smoke have more lung illnesses, such as bronchitis and pneumonia, and can develop asthma. And because smoking parents are more likely to cough and spread germs, their children are more likely to develop chest illnesses. Exposure to tobacco smoke also increases the risk of heart disease.