The Cooper Institute Insights
Steve Farrell, Ph.D.
Cardiorespiratory Fitness Level and The Metabolic Syndrome in Women

 

Overview
Cardiovascular disease (CVD) is the leading cause of death in U.S. women, accounting for over 500,000 deaths annually.  CVD includes all diseases of the heart and circulatory system.  Coronary heart disease (heart attack, bypass surgery) and cerebrovascular disease (stroke) are two common types of CVD.  There are several risk factors (predictors) of heart attack and stroke, including such things as abnormal blood cholesterol level, hypertension, smoking, sedentary lifestyle, diabetes, family history, obesity, elevated blood triglyceride levels and stress.  In the 1980s researchers began to notice that several of these risk factors tend to cluster together in some individuals.

Metabolic syndrome
In 1988, Stanford endocrinologist Gerald Reaven, M.D., coined the term “metabolic syndrome” to describe the condition where certain risk factors cluster together.  The table below identifies the five components and cutpoints for identifying metabolic syndrome in males and females.  Individuals with three or more of the five components are considered to have metabolic syndrome.

According to the latest government statistics, approximately 47 million Americans have metabolic syndrome.  Having metabolic syndrome significantly increases the risk of developing CVD, particular in people who are unfit and sedentary. 

What causes metabolic syndrome?
People with metabolic syndrome have been shown to be insulin resistant.  Insulin is a hormone produced by the pancreas, and it normally helps transport glucose (sugar) from the blood into the cells.  The glucose is then used by the cells as an energy source.  The process of transporting glucose from the blood into the cells does not work well in some people because they are resistant to the normal effects of insulin.  The pancreas will typically respond by producing more insulin to try to get the glucose transport job done.  Unfortunately, excess insulin production has an adverse effect on blood pressure, HDL cholesterol, and blood triglyceride levels.  This in turn increases the risk of developing CVD.

What causes insulin resistance?
More often than not, individuals who are insulin resistant are overweight and sedentary.  When these factors are combined with a genetic predisposition for insulin resistance, most of these individuals will develop metabolic syndrome.  

Cardiorespiratory fitness level and metabolic syndrome in women
In the May 21, 2004 issue of Obesity Research, The Cooper Institute published a paper examining the prevalence of metabolic syndrome in women of varying fitness levels and ages.  We studied a group of 7,104 Cooper Clinic female patients with an average age of 45 years who came to the Clinic between 1979 and 2000.  Cardiorespiratory fitness level (CRF) was measured with a maximal treadmill exercise test, and women were divided into five fitness categories based on their age and treadmill performance.  Blood tests, as well as measures of abdominal girth and blood pressure were used to identify women with metabolic syndrome.  Low CRF was a strong predictor of the presence of metabolic syndrome.  When examining the women from the lowest to the highest of the five fitness categories, metabolic syndrome was present in 19 percent, 6.7 percent, 6.0 percent, 3.6 percent, and 2.3 percent of the women respectively.  Age was also a strong predictor of the presence of metabolic syndrome; only 2.4 percent of 20-to-29 year old women were found to have metabolic syndrome, compared to over 15 percent of women ages 60 and older.

It became clear that low CRF levels are strongly related to the risk of having metabolic syndrome.  The results of this study should lead physicians and other health care professionals to spend more time counseling their sedentary female patients to become more physically active. Simply moving from the lowest fitness category (19 percent had metabolic syndrome) to the next highest fitness category (6.7 percent had metabolic syndrome) decreased the likelihood of having metabolic syndrome by nearly three-fold.  This can be accomplished by just being moderately active for at least 30 minutes a day, and it doesn’t have to be done all at once.

Only one other previously published study on this topic in women exists.  That study used only 146 women compared to 7,104 in The Cooper Institute study.

Founded by Kenneth H. Cooper, M.D., M.P.H., in 1970, The Cooper Institute is an international leader in preventive medicine research.  Areas of research include epidemiology, exercise physiology, behavior change, cancer prevention, children’s health, obesity, nutrition, aging, diabetes, hypertension, weight management, health communication, and other health issues. 

Steven Farrell, Ph.D., is curriculum director for The Cooper Institute's department of Education and Certification.  The Division of Education and Certification offers training and certification programs to help health, fitness, and medical professionals put research-based principles developed at The Cooper Institute into practice. There are more than 18 class offerings presented in Dallas and in other cities. The Institute instructs and certifies more than 6,500 professionals annually, as well as all branches of the United States military.  For more information about classes, products, and services, visit www.cooperinst.org, or call the Division of Education and Certification at 1-800-635-7050.

To receive The Cooper Institute newsletter, contact Barb McGowan, director of development at bmcgowan@cooperinst.org.