Companies can save millions in health-care costs simply by encouraging their employees to exercise a little bit, researchers reported on Friday.

They said obese employees have higher health-care costs, but lowered those expenses by exercising just a couple of times a week - without even losing any weight.

Feifei Wang and colleagues at the University of Michigan studied 23,500 workers at General Motors.

They estimated that getting the most sedentary obese workers to exercise would have saved about $790,000 a year, or about 1.5 percent of health-care costs for the whole group.

Company-wide, the potential savings could reach $7.1 million per year, they reported in the Journal of Occupational and Environmental Medicine.

Of the whole group of workers, about 30 percent were of normal weight, 45 percent were overweight, and 25 percent were obese. Annual health-care costs averaged $2,200 for normal weight, $2,400 for the overweight, and $2,700 for obese employees.

But among workers who did no exercise, health-care costs went up by at least $100 a year, and were $3,000 a year for obese employees who were sedentary.

But adding two or more days of light exercise - at least 20 minutes of exercise or work hard enough to increase heart rate and breathing - lowered costs by on average $500 per employee a year, the researchers found.

“This indicates that physical activity behavior could offset at least some of the adverse effects of excess body fat, and in consequence, help moderate the escalating health-care costs,” Wang and colleagues wrote.

SOURCE: Journal of Occupational and Environmental Medicine, May 2004.