Workaholics take note: working long hours raises the risk of heart disease by up to 80 percent, scientists claim.

Employees who frequently put in overtime are significantly more likely to suffer heart attacks and strokes, according to a new major study.

The findings, published in the American Journal of Epidemiology, show that a combination of stress, raised blood pressure and unhealthy diets from toiling long working hours may be sentencing thousands of employees to premature heart problems.

The recent meta-analysis, which combined the results of different studies over the last 50 years and found that spending too long in the office resulted in a 40 to 80 percent greater chance of heart disease compared to sticking to a normal eight hour day.

The latest findings discovered by scientists at the Finnish Institute of Occupational Health support results from a 2011 British survey that revealed that doing more than 11 hours of work a day raised heart disease risks by 67 percent.

Lead researcher Dr. Marianna Virtanen and her team gathered data from 12 different studies going back to 1958, when researchers first suggested that working long hours could be linked to poor heart health. In total, the studies involved more than 22,000 participants, from Britain, the USA, Japan, Sweden, Finland, Denmark and the Netherlands.

After matching up the results from all the studies, Dr. Virtanen and her colleagues found that participants working the longest hours were between 40 percent and 80 percent more likely to develop heart disease than colleagues who worked shorter periods.

Investigators noted that the risks differed according to how studies were conducted, but they noted that the risk for heart disease was the greatest in studies where participants were asked to recall their working hours.

However, in studies where researchers closely monitored participants' working hours, which is regarded as a more accurate method, this risk was around 40 percent.

"There are several potential mechanisms that may underlie the association between long working hours and heart disease," study authors wrote. "One is prolonged exposure to psychological stress."

Researchers said that other factors could be increased levels of the stress hormone cortisol, poor eating habits and lack of physical activity due to limited leisure time.

In 2009, Dr. Virtanen and her team also found that long working hours was just as bad as smoking in raising the risk of dementia later in life.

They found that middle-aged workers working 55 hours or more a week had poorer brain function than those clocking up no more than 40 hours. Participants who worked longer hours scored lower on tests to measure intelligence, short-term memory and word recall.