More recently, in the May 2003 British Medical Journal, researchers found that passive smoke had no significant connection with heart disease or lung cancer death at any level of exposure at any time.
Ever since I saw "Harlan County, USA", I've been leery about "researchers' studies" when I'm not sure about whose agenda they're trying to prove. In the documentary about the Harlan County coal mine strikes in the early 70's, the company came up with a study that said there was no correlation between black lung disease and working in a coal mine.