May 8, 2003 -- Among overweight people, life-threatening blood clots are common. But exercise can help dissolve blood clots.

That's the finding from a new study, presented at an American Heart Association meeting this week.

Obese people are at an increased risk of blood clots and diseases such as stroke. This study helps explain why these complications are occurring in obese people and that simply exercising may help dissolve blood clots.

In the study, Colorado investigators looked at 36 sedentary men, all about 60 years old -- 12 of whom were lean and 24 obese. Researchers measured the amounts of a critical blood clot dissolver called tissue-type plasminogen activator (t-PA). The overweight men had "significantly blunted" levels of t-PA -- 30% less than the lean men.

However, once the men got active -- three months of walking about 45 minutes a day, five days a week -- 10 of the obese men had a 50% higher release of blood clot-dissolving t-PA. In fact, exercise raised their levels similar to those of the lean men.

Regular aerobic exercise helps reverse blood clot formation, concludes lead researcher Derek T. Smith, with the University of Colorado Health Sciences Center.