U.S. tobacco companies worked to discredit research showing the ill health effects of secondhand smoke, according to California researchers who reviewed a cache of secret industry documents.

The Sacramento Bee reported Oct. 16 that researchers Eliza Tong of the University of California at Davis and Stanton Glantz of the University of California at San Francisco also detailed how the industry relied on dubious research to back claims of producing "reduced risk" cigarettes.

The authors reviewed about 5,000 internal industry documents, including 47 dealing with the link between secondhand smoke and heart disease, and concluded that the industry actively suppressed research with negative findings, such as failing to publish complete results of studies or attributing ill health effects to stress and factors other than tobacco smoke.

"This special report exposes the deceitful practices of the tobacco industry in its attempts to fight smoke-free regulations and serves as an eye-opener for the public-health community and the federal government as the 'reduced-harm product' debate picks up steam," said M. Cass Wheeler, CEO of the American Heart Association.

"I think they are still trying to frame the issue to minimize the risks," said Tong. "Secondhand smoke does cause cardiovascular disease, and any research by tobacco industry should be treated with skepticism."

The report was published in the October 2007 issue of the journal Circulation.