In yet another study showing that long workdays lead to poorer health, a study of London office workers found that people who regularly worked 11 hours a day or longer had a 67% higher risk of developing heart disease, compared to people who worked seven to eight hour days.

If more research continues to support the idea that longer workdays lead to heart disease, asking about this could become part of a standard physical exam.

This isn't totally unexpected information. Prior studies in Europe and Japan have shown links between long work hours and heart attacks. And other studies have shown that job stress, in the form of having little decision making power or control over work, leads to an increased risk of developing heart disease. What this study does is suggest a way to use that information.

Right now, doctors use a measure called the Framingham score to estimate a person's future risk of developing heart disease. It's based on factors such as a person's age, sex, blood pressure, cholesterol level and whether or not they smoke. But it doesn't take into account work-related factors, like the length of the workday.

When the researchers added information about workday length to workers' Framingham scores, about 5% of the people who had previously been classed as low-risk were seen to be at higher risk of heart disease. Had this been known, they might have been treated more aggressively, either through medication or work-related changes. And maybe they wouldn't have developed heart disease later on.

A little over 10% of the workers worked 11 hours a day or longer, including work they took home with them.

The researchers stress that this and other studies don't show a cause and effect relationship between piling up the overtime and developing heart disease, they merely suggest one. It's well known that smoking raises the risk of heart disease; fewer studies have been done on work-related risk factors.

If more research continues to support the idea that longer workdays lead to heart disease, asking about this could become part of a standard physical exam. And the way doctors judge heart risk could be modified to take long workdays into account.

The researchers used data from the Whitehall II study. This followed a group of nearly 7,100 London civil service workers, a population with an overall low-risk of developing heart disease. Worker age ranged from 39 to 62. About 70% were men and 91% were white. After an initial medical exam, workers who already had heart disease were excluded from the study. Workers were then followed for over 12 years. During this time, 192 developed heart disease.

After taking their Framingham scores from their initial medical exam into account, those who regularly worked 11-hour or longer days were 67% more likely to have developed heart disease. Adding workday length information to the traditional Framingham scores would have reclassified about 5% of the workers from low-risk to higher risk. And steps could have been taken to address this risk.

Right now, telling your boss that you have to shorten your workday so you don't get heart disease 10 years down the road isn't likely to get you much sympathy. If more studies back up the London study, it might become a normal part of everyday business culture.

An article on the study was published in the April 5, 2011 issue of Annals of Internal Medicine.