An eleven hour day instead of an eight hour one could give you a two thirds increased risk of a heart attack, according to a new study.

Boffins at University College London studied Whitehall employees over a period of 11 years. 192 of their subjects suffered heart attacks during the period. While it is not entirely clear what causes the increased risk, it is thought that increased levels of the stress hormone cortisol has something to do with it.

Professor Mika Kivimäki said: ‘We have shown that working long days is associated with a remarkable increase in risk of heart disease. It could also be a wake-up call for people who overwork, especially if they already have other risk factors.’

Another professor, Professor Stephen Holgate from the Medical Research Foundation, added: ‘This study might make us think twice about the old adage 'hard work won't kill you'. It's crucial that we invest in long term studies like the Whitehall II study, which has been running for over a quarter of a century, to test our preconceptions about what really is good or bad for our health.’