If you work long overtime hours, you may want to think about reducing them, if at all possible. Working three to four hours of overtime per day ups one’s risk for heart-related deaths significantly, reports a new study in the May 11, 2010 online edition of the European Heart Journal.

The results were striking: for people who worked between three and four hours of overtime every day, their risk of developing heart problems rose by 60%, compared to those who did no overtime.

The British study followed over 6,000 civil servants for an average 11 years, noting how many hours of overtime the participants tended to put in every day. The researchers, led by Marianna Virtanen, also tracked how many of the participants died from coronary heart disease, or suffered from nonfatal heart attack or angina (chest pain). They found that of the entire cohort, 369 fell victim to one of these three phenomena over the course of the study.

The results were striking: for people who worked between three and four hours of overtime every day, their risk of developing heart problems rose by 60%, compared to those who did no overtime. But these results were not seen for people who only worked one to two hours of overtime. The results held true after the researchers controlled for other factors, like age, marital status, and sex. When the researchers looked at the relationship between working overtime and the risk of death from any cause, they found only a small effect that was not statistically significant, meaning that it could have been due to chance.

Though the findings may seem somewhat intuitive, what’s the mechanism behind them? The researchers say that part of the effect may be due to the fact that people who were considered Type A personalities were more likely to work long over-time hours. When the team controlled for personality type, they found the relationship between working over-time and heart problems to be reduced by 11-12%, which suggests that personality type may indeed play a role. People who are considered Type A are more likely to suffer from depression and anxiety, write the researchers, which has already been shown to increase the risk of coronary heart disease by itself. The researchers also suggest that lack of sleep and/or the ability to relax or unwind may also be at play.

The researchers point out that overtime has increased quite notably in recent history, and the U.S. is one of the countries in which the number of work hours has grown the most markedly. If you routinely work long hours, it may be advisable to cut them back, if possible – or if it is not, look into effective ways to relax, reduce stress and anxiety, and catch up on sleep.