A new study of 600,000 individuals in Australia, the United States, and Europe published in the Lancet, a United Kingdom-based medical journal, found that people who more more than 55 hours per week or more have a 33% greater risk of stroke and a 13% greater risk of coronary heart disease.

The study concludes that “more attention should be paid to the management of vascular risk factors in individuals who work long hours.”

The study is the largest so far to examine the relationship between working hours and cardiovascular health and is especially noteworthy because it points to stroke as a risk of working long hours. Earlier studies have linked heart attacks to excessive work.

There are critics of the study, though. Stephen Kopecky, a professor of medicine in the division of cardiology at the Mayo Clinic, told The New York Times, that the analysis did not fully account for the effects of cholesterol, family history, and blood pressure in all cases, so it is possible that long hours are not the only cause of the increased health risks.