ATLANTA -- At least 8.6 million Americans are living with chronic bronchitis, emphysema and other serious smoking-related illnesses, according to a new study that paints a dark picture of the health risks of tobacco.

The study, the first to estimate the number of people in the United States who have serious lung disorders or other diseases caused by cigarettes, was published by the Centers for Disease Control and Prevention on Thursday.

Researchers said the findings underscored a need to expand anti-tobacco programs and increase surveillance of smoking habits in the nation. There are about 46.5 million smokers in the United States.

The CDC considers cigarette smoking to be the leading preventable cause of death in the nation. About 440,000 people die each year from lung cancer and other diseases related to tobacco use.

The new study found that more than 4.5 million smokers and non-smokers reported having chronic bronchitis in 2000, making it the most prevalent disease in these groups. Bronchitis is often marked by a steady recurrent cough.

More than three million people said they had emphysema, whose symptoms include chronic shortness of breath.

But Terry Pechacek, the CDC's associate director of science, said those estimates were conservative because they relied to a large degree on self-reporting by respondents who participated in various surveys.

"Many smokers are in some degree of denial, so we know that this is an underestimate," Pechacek told Reuters.

In addition to highlighting the enormous human cost of cigarette smoking, the study noted that smoking was costing the nation $75 billion in direct medical costs and $82 billion in lost productivity each year.

The study comes at a time when casual smoking appears to be on the rise in the nation.

Anti-smoking advocates say the human and economic costs of smoking could be dramatically reduced if authorities clamped down on tobacco advertising and raised taxes on cigarettes to make them less affordable, particularly to young people.

"We know how to prevent so much of this tobacco-caused disease and death, but public officials have not passed the policies or devoted the resources to get the job done," said Vince Willmore, a spokesman for the Washington-based anti-tobacco group Campaign for Tobacco-Free Kids.