MONDAY, Nov. 21 (HealthDay News) -- Physically unfit men who do heavy work may be at increased risk for fatal heart attack, a new study says.

It also found that income did not influence this risk, even though men in lower socioeconomic levels are more likely to have lifestyle risk factors such as obesity and smoking.

Danish researchers compared men in lower and higher socioeconomic levels. Thirty percent of the men in the lower socioeconomic group did heavy physical work, compared with 3.5 percent of those in the higher socioeconomic group.

Men in the lower social classes had a 14 percent long-term risk for death from ischemic heart disease (such as heart attack) compared with about 9 percent for those in the higher social classes.

But poor physical fitness, not low social class, was the main risk factor. Overall, men with poor fitness who did heavy work were nearly three times more likely to die from ischemic heart disease than those who did light physical work. Fit men who did heavy work were about 40 percent less likely to die from heart disease than unfit men who did heavy work.

"These observations indicate that physical fitness is a protector of or a risk modifier among men exposed to high physical loads on their cardiovascular system," wrote Andreas Holtermann, of Bispebjerg University Hospital in Copenhagen, and colleagues.

The study appears in the November issue of the Journal of Occupational and Environmental Medicine.

More information

The U.S. National Heart, Lung, and Blood Institute offers a guide to a healthy heart.