The British White Hall II Prosective Cohort Study study suggests working regular overtime increases your risk for heart disease. Over 6,000 men and women working as civil servants were looked at. The study began in 1985 and ran for 11 years.
Those working 10 -12 hours per day had an increased risk of developing serious heart disease. It seemed that working 8 – 10 per day did not have an effect on peoples cardiac health in a negative way.
The study design is a Prospective Cohort study. Simply, it is a form of a long term study looking at a group of people with a common experiance. Keep in mind that this type of study should be compared to another kind of study, called a cross sectional study.
To learn more you can look at the White Hall Findings