Smokers in their 30s and 40s have five times as many heart attacks as non-smokers, according to the largest study in the world of heart attack survivors. The Medical Research Council, British Heart Foundation and Imperial Cancer Research Fund clinical trial service unit at Oxford University tomorrow publishes a report in the British Medical Journal on its five-year survey of 14,000 survivors and 32,000 relatives who had not had heart attacks. "This study shows that smoking causes even more premature heart attacks than was previously supposed," said Rory Collins, British Heart Foundation senior research fellow at Oxford.