Workers who clocked more than 51 hours at the office each week were 29 percent more likely to have high blood pressure than those who worked 39 hours or less, a new study from California has found.

Nearly all past research linking long work hours and high blood pressure has been done among Asian workers, Dr. Haiou Yang of the University of California in Irvine and colleagues note in their report in the journal Hypertension.

Interest in the topic began in Japan, they add, where a notoriously high-pressure work culture has given rise to a phenomenon known as Karoshi, or "sudden death from overwork." Today, Americans work longer hours than do Japanese, the researchers add.

To investigate whether more time on the job could drive up hypertension risk among Westerners, the researchers looked at a representative sample of 24,305 California adults who worked 11 hours or more each week.

The likelihood of having high blood pressure rose steadily with the number of hours worked, the researchers found, and persisted even after adjusting for factors such as socioeconomic status and body weight.

Those who worked 40 hours per week were 14 percent more likely to have high blood pressure than people who worked 39 hours or less. Hypertension risk was 17 percent greater in those working 41 to 50 hours weekly, and 29 percent higher in those working 51 hours or more.

The researchers also found that hypertension was more common among clerical and unskilled workers than among professionals. This "suggests that occupations requiring more challenging and mentally active work may have a protective effect against hypertension," Yang and his colleagues write.

Almost all of the developed world has legislation limiting work hours, except for the United States, the researchers note.

SOURCE: Hypertension: Journal of the American Heart Association, online August 28, 2006.

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