When people stop doing any regular physical activity, they begin to lose any accrued health benefits almost immediately, according to a new study.

Within two weeks of cutting back on physical activity, healthy volunteers in the study experienced metabolic changes associated with diabetes, coronary disease, and other conditions, reports Rikke Krogh-Madsen, M.D., of Copenhagen's Center of Inflammation and Metabolism, and colleagues in the March 19 issue of the Journal of the American Medical Association.

Although the study was small, its findings support previous data indicating that precipitous reductions in physical activity may contribute directly to the development of chronic diseases.

"Our findings indicated that if there is a lack of normal physical activity, a person greatly increases the chances of developing a chronic disease," said co-author Frank Booth, Ph.D., of the University of Missouri in Columbia. "Previously, we thought that not exercising just wasn't healthy, but we didn't think that a lack of activity could cause disease. That assumption was wrong."

The study looked at 18 healthy men, who were asked to reduce their normal level of daily activity, which was measured by the number of steps walked. They did this by riding an elevator instead of climbing stairs, or riding in a car instead of walking.

Eight participants reduced their pedometer-counted daily steps from an average of 6,203 to 1,394. Laboratory values and other measurements were obtained at baseline and after seven, 14 and 22 days of reduced activity. The other 10 participants reduced their daily physical activity from 10,501 steps to 1,344.

The participants underwent oral glucose tolerance tests before the study and during the specified follow-up visits. Plasma insulin levels were also taken.

Additionally, the 10 men required to make larger reductions in physical activity also had oral fat tolerance tests before the study and on day 12, measurement of plasma triglycerides and C-reactive protein, MRI assessment of intra-abdominal fat, and dual x-ray absorptiometry evaluation of body composition.

After only two or three weeks, the study participants "developed metabolic changes suggestive of decreased insulin sensitivity and attenuation of postprandial lipid metabolism and physical changes that suggest that calories used to maintain muscle mass with greater stepping may have been partitioned to visceral fat," the authors concluded.

"If confirmed, these abnormalities could represent a link between reduced exercise and the risks that have been associated with the progression of chronic disorders and premature mortality."