Early results of the Whitehall study of 10,340 civil servants show that it is the lowest grades who are most likely to be affected by stress-linked heart disease.
Michael Marmot, professor of epidemiology and public health at University College and Middlesex School of Medicine, said that lack of control over daily events seemed to be the key to harmful stress at work.
It was true that 30 years ago the heart disease epidemic took its toll on executives. Then, they smoked more, ate a richer diet and took less exercise than people in lower social classes, he said yesterday, before the annual meeting of the British Heart Foundation.
While smoking, fat and lack of exercise continued to be important risk factors for everyone, researchers were trying to tease out other complex reasons to explain why some people suffered from heart disease and others did not, Professor Marmot said.
The British Heart Foundation has given a further pounds 500,000 to the Whitehall II study. The subjects are examined for angina and asked about their work, lifestyle, domestic, social and financial circumstances.
Professor Marmot said: 'The lowest grades had three times the heart disease mortality of the highest grade and the difference was not adequately explained by variations in smoking habits. We have found the lower the employment grade, the higher the prevalence of angina, inadequate blood supply and chronic bronchitis.'
The findings support Swedish studies showing a direct link between stress and blood clotting. The suggested chain of events is that lower social position leads to poorer working conditions, where overwork and lack of control are more likely. Increased heart disease levels appear to follow.
The lowest grades of worker in the English study have higher levels of fibrinogen in their blood, the substance which leads to the formation of blood clots.
'It seems that people who are hostile are more likely to have heart attacks, and hostility was more common in the lower groups,' Professor Marmot said.