London: Working 55 hours or more a week can increase the chances of suffering a stroke by a third compared to a 35-40 hour work week, a large new study involving over 500,000 people has warned, says PTI. Mika Kivimaki, Professor of Epidemiology at University College London, UK, and colleagues did a systematic review and meta-analysis of published studies and unpublished individual-level data examining the effects of longer working hours on cardiovascular disease up to August 20, 2014. Analysis of data from 25 studies involving 603,838 men and women from Europe, the US, and Australia who were followed for an average of 8.5 years, found a 13 per cent increased risk of incident coronary heart disease (a new diagnosis, hospitalisation, or death) in people working 55 hours or more per week compared with those putting in a normal 35 to 40 hour week, after taking into account risk factors like age, sex, socioeconomic status.