By Megan Gannon, News Editor

Published: 10/14/2014 03:01 PM EDT on LiveScience

Smoking is to blame for about 14 million major medical conditions among American adults yearly, a new study shows.

That number is higher than the U.S. Centers for Disease Control and Prevention's (CDC) last estimate, in the year 2000, which found that American adults suffered from 12.7 million smoking-attributable conditions.

Chronic obstructive pulmonary disease (COPD) — which includes conditions like chronic bronchitis and emphysema — accounts for more than half of the medical cases attributable to smoking, the researchers found.

"The disease burden of cigarette smoking in the United States remains immense, and updated estimates indicate that COPD may be substantially underreported in health survey data," wrote the researchers, who published their findings yesterday (Oct. 13) in the journal JAMA Internal Medicine. [Top 10 Leading Causes of Death]

Data from the CDC's National Health Interview Survey initially suggested that 6.9 million adults in the United States suffered from a combined 10.9 million smoking-attributable medical conditions, including COPD, cancers, heart attacks and diabetes. But the actual number of conditions is likely higher because this survey relies on people's self-reports, and COPD is underreported, the researchers said.

To account for this gap, the researchers — led by Brian Rostron, of the U.S. Food and Drug Administration's Center for Tobacco Products — also looked at data from another CDC survey, the National Health and Nutrition Examination Survey. In this survey program, participants are not only interviewed, but they also undergo physical exams, including a lung function test called spirometry that is used to diagnose COPD.

Based on that data, Rostron and colleagues estimated that cases of COPD were 70 percent higher than the number of cases based on self-reported data. The researchers estimated that 14 million American adults had a smoking-related condition in 2009.

The lack of COPD diagnoses might be the result of current clinical guidelines, the researchers said. Physicians are advised to use spirometry to test patients who report symptoms such as wheezing and chronic cough. But doctors are advised not to screen patients who don't report these symptoms because of the economic and health care costs.

"Individuals with slowly declining respiratory function or individuals who have become accustomed to some degree of chronic airway obstruction may not report these conditions to physicians and consequently would not be screened for or diagnosed with COPD," the authors of the study wrote.

Smoking is considered the leading cause of preventable death in the United States. Cigarette smoke contains dozens of known carcinogens. Smoking is the cause of 90 percent of lung cancers, and has also been linked to cancers in several other organs, including, most recently, the liver and colon.

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