FRIDAY, Sept. 10 (HealthDay News) -- Compared with men who work less than 40 hours per week, men with low physical fitness working more than 45 hours per week are at increased risk of ischemic heart disease (IHD) mortality, but this is not the case for men with intermediate or high fitness levels who work long hours, according to a study published online Sept. 6 in Heart.

Andreas Holtermann, Ph.D., of the National Research Centre for the Working Environment in Copenhagen, Denmark, and colleagues evaluated 5,249 gainfully employed men between 40 and 59 years of age over 30 years of follow-up. The men were part of the Copenhagen Male Study.

The investigators found that 587 men (11.9 percent) died due to IHD. After adjustment for confounding variables, Cox analyses revealed that working more than 45 hours per week was linked to a higher risk of IHD mortality in the least fit (hazard ratio [HR], 2.28), but not intermediate (HR, 0.94) and most fit men (HR, 0.91), compared with men working less than 40 hours per week.

"The finding that working more than 45 hours/week is associated with a more than doubled risk of IHD mortality among men with low physical fitness, and not among men with mediate or high physical fitness is a new observation," the authors write. "If the relationship is causal, it obviously has major implications in the prevention of cardiovascular disease."

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