Exercise Inhibits Cells That Trigger Arterial Disease

Exercise has long been known to protect against heart disease by helping to control weight, reducing blood pressure, lowering triglyceride levels, and increasing levels of high density lipoprotein (HDL), or ``good'' cholesterol, but the exact mechanism of exercise's heart-healthy effect is still not completely understood.

Increasing evidence suggests that the development of fatty plaques --which are comprised of layers of fat, calcium, cholesterol, fibrous tissue, and blood cells -- may, in fact, be triggered by an immune response. Immune cells called mononuclear cells found in early arterial plaques produce proteins called cytokines. Some cytokines appear to assist in the buildup of these plaques, and some prevent this buildup.

To test if exercise influenced the levels of cytokine production by these immune cells, study authors Dr. J. Kelly Smith, of East Tennessee State University, Johnson City, Tennessee, and colleagues enlisted 43 people considered at risk of developing heart disease to participate in a 6-month supervised exercise program.

After the study participants engaged in exercises such as weight lifting, treadmill walking, and cycling for an average of 2.5 hours per week for 6 months, Kelly and colleagues observed significant heart protective changes in levels of these cells. Moreover, the extent of these changes appeared to be proportional to the amount of time the participants had spent exercising.

On average, the study results show that exercise led to a 58% drop in the production of cytokines known to contribute to fatty plaque development, while the production of cytokines that inhibit the development of fatty plaques rose by nearly 36%.

Kelly and colleagues are not sure why exercise had the impact it did.  They suggest that exercise may stimulate the immune system to fight off infectious agents that may trigger arterial disease. Or exercise may reduce the risk of fatty buildup on arterial walls by reducing levels of LDL (''bad'') cholesterol, believed to play a role in this buildup.

But they conclude that the study ``provides an insight as to how physical activity helps protect against (heart disease).''

``Children and adults alike should set a goal of accumulating at least 30 minutes of moderate-intensity physical activity on most, and preferably all, days of the week,'' note the researchers, quoting from National Institutes of Health recommendations.

Heart disease deaths have declined over the past 25 years, but coronary artery disease remains the leading cause of death in the US and much of the industrialized world.

SOURCE: The Journal of the American Medical Association
1999;281:1722-1727.

Copyright © 2001 by John Loeschhorn - Mail to:mtnrnr@pacbell.net February 11, 2001