People working long hours are more likely to have a stroke, according to analysis of more than half a million people.
The data, published in the Lancet medical journal, showed the chance of a stroke increased beyond the traditional 9am to 5pm.
The link is uncertain, but theories include a stressful job and the damaging impact on lifestyle.
Experts said people working long hours should monitor their blood pressure
The study showed that in comparison to a 35-40 hour week, doing up to 48 hours increased the risk by 10%, up to 54 hours by 27% and over 55 hours by 33%.
Dr Mika Kivimaki, from University College London, said that in the 35-40 hour group there were fewer than five strokes per 1,000 employees per decade.
And that increased to six strokes per 1,000 employees per decade in those working 55 hours or more.
BBC News website
Source: BBC News