by Anthony J. Brown, MD

Last Updated: 2008-04-04 9:00:01 -0400 (Reuters Health)

NEW YORK (Reuters Health) – Elderly individuals who engage in strenuous exercise, such as jogging, are at heightened risk for venous thrombosis compared with their sedentary peers, according to the results of a new study. Still, the authors assert, the benefits of moderate or strenuous exercise in elderly individuals likely outweigh this risk.

Prior observational studies have yielded conflicting results regarding the impact of exercise on the risk of venous thrombosis, according to the report in the Journal of the American Geriatrics Society for March. However, the main studies investigating this topic did not provide a detailed analysis of exercise or careful control of potential confounding factors.

The current investigation by Dr. Susan R. Heckbert of the University of Washington, Seattle, and colleagues involved an analysis of data for 5534 subjects, 65 years and older, without prior venous thromboembolism who were enrolled in the Cardiovascular Health Study and were followed for a median of 11.6 years.

Self-reported exercise was assessed two or three times during follow-up. "The amount of exercise was categorized in three different ways," the investigators explain: as exercise versus no exercise based on a minimum expenditure of 500 kcal/week; as kilocalories expended per week; and as none or mild, moderate, or strenuous in intensity.

Exercise intensity was graded using metabolic equivalent levels. Activities with a MET level below 4, like walking, were considered low intensity. Gymnastics and other activities with a MET level of 4 to 6 were classified as moderate intensity. Activities with a MET level above 6 were classified as strenuous, such as jogging.

During follow-up, 171 patients developed a first venous thrombosis, the report indicates.

After adjusting for gender, age, race, self-reported health, and body mass index, exercise at baseline was not a significant predictor of venous thrombosis. However, when exercise was modeled as a time-varying exposure, there was a suggestion of an elevated thrombosis risk.

Further analysis showed a nonsignificant reduction in thrombosis risk with mild-intensity exercise, such as walking, with an adjusted hazard ratio of 0.75. By contrast, jogging and other strenuous activities increased the risk of venous thromboembolism significantly (adjusted HR = 1.75) relative to no exercise at all.

Despite these findings, Dr. Heckbert and colleagues conclude: "The overall benefits of exercise likely outweigh the possible higher risks of venous thrombosis or injuries, but more research is needed to investigate this unexpected higher risk of venous thrombosis in elderly people associated with strenuous-intensity exercise."

J Am Geriatr Soc 2008;56:517-522.

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