After combing through nearly 50 million pages of previously secret, internal tobacco-industry documents, UC Davis and UC San Francisco researchers say they have documented for the first time how the industry funded and used scientific studies to undermine evidence linking secondhand smoke to cardiovascular disease.

In a special report published in the Oct. 16 issue of the journal Circulation, Elisa Tong and Stanton Glantz wrote that the tobacco-related documents show how the industry initially worked to question scientific evidence about the harmful effects of secondhand smoke as a way to fight smoke-free regulations. More recently, the researchers suggest, tobacco-company-funded studies have been conducted to support the development of so-called "reduced-harm" cigarettes.

"Our analysis of the documents indicates an industry that also wants to influence the debate about how 'reduced-harm' tobacco products should be evaluated," said Tong, an assistant professor of internal medicine at the UC Davis School of Medicine and lead author of the study. "It's not just about fighting smoke-free regulations.."

Tong conducted a computerized search involving millions of pages of tobacco-industry materials, including memos, letters and scientific reports. The documents are publicly available as part of several major legal settlements in recent years. Of the 5,000 documents ultimately reviewed, she identified 47 closely tied to secondhand smoke and cardiovascular disease issues.

Co-author Glantz, a professor of medicine in the cardiology division at UCSF and director of the university's Center for Tobacco Control Research and Education, helped analyze the information and develop a detailed picture of tobacco-industry practices.

The documents show how tobacco companies funded epidemiological and biological research that was designed to support claims that secondhand smoke posed little or no harm. The Circulation article describes how industry-funded studies misclassified study subjects as nonsmokers when they were actually "passive smokers" who were being exposed to background air filled with secondhand smoke. This type of misclassification helped bias study results against finding an effect from secondhand smoke. The results were used to call into question other evidence linking secondhand smoke to the increased risks of cardiovascular disease.

Such studies, the authors said, were often published in scientific journals that had industry representatives on their editorial boards. "The true level of the tobacco industry's involvement in such studies was rarely disclosed in an adequate manner," Glantz said.

Tong and Glantz said the tobacco industry suppressed unfavorable research results. The report cites a 1995 industry study that found that nonsmokers exposed to more than seven hours of secondhand smoke suffered statistically significant changes in blood lipids, inflammatory markers, pulmonary function tests and urinary mutagenicity. Those findings, Tong and Glantz said, appear to have been briefly revealed at a conference and only partially published elsewhere.

Tong and Glantz suggested that one of the key reasons why tobacco companies have hindered efforts to ban smoking in public places is to maintain corporate viability in the marketplace. They noted that smoke-free workplace rules can reduce cigarette consumption among smokers by approximately three cigarettes per day, or about 30 percent.

An American Heart Association Western States Postdoctoral Fellowship and a grant from the National Cancer Institute funded the Circulation study. UC San Francisco's Legacy Tobacco Document Library was the primary source for industry documents.

ON THE NET: circ.ahajournals.org

Casey is a senior public information representative for the UC Davis Health System.