Background
Previous studies reveal that African American girls are more likely to be overweight than Caucasian girls. The trend continues into their adulthood, as 30 percent of younger (18-30 years) and 77 percent of older (45-65 years) black women are obese compared to 14 percent and 46 percent respectively, for their white counterparts. Overall, black women are 60 percent more likely to become obese than are white women. Women in minority groups are less physically active than the general American population, and the overall health status of people of color, including African American women, is lower than that of the general America population.
Obesity can lead to cardiovascular problems. Another disorder of the heart is Long QT Syndrome (LQTS), an inherited or acquired condition of the heart’s electrical system. People with LQTS are at risk for syncope (loss of consciousness) and sudden death, often at a young age. Although it is known that African Americans have a higher incidence of obesity compared to Caucasians, race-specific information is not available for the prevalence of LQTS. Furthermore, while it is well known that chronic physical activity reduces the incidence of obesity, little is known about the effects of chronic physical activity on QT (time from electrocardiogram Q wave to the end of the T wave corresponding to electrical systole, or contraction and relaxation of the ventricles) duration.
A new research study, “QTc is Related to Obesity and Physical Activity Level for African American Females,” has been conducted by C. Jayne Brahler, Ph.D., Janine T. Baer. Ph.D., R.D. and Patricia A. Dolan, RD., from the University of Dayton, Dayton, Ohio; and reported by Dr. Brahler and Akbar Shah MD, from Cardiology South, Inc., Kettering, Ohio, and Emily C. Johnson, Ph.D., of the Department of Exercise Science, Washington State University, Pullman, WA. The investigators will present their findings in detail during the American Physiological Society (APS) annual meeting, which is being held as part of the Experimental Biology (EB ’02) meeting. More than 12,000 scientific investigators are attending the conference, which begins April 20-24, 2002 at the Ernest N. Morial Convention Center, New Orleans, LA.
Methodology
The subjects were 44 low-income African American women (ages 21-53 years) and 66 biological daughters (ages 5-17 years). Eligibility criteria included pre-menopausal, not on estrogen therapy, not pregnant, and apparently healthy and medically stable, with no known acute heart disease complications, endocrine problems, complications from diabetes mellitus, HIV/AIDS, or other major diseases as determined by completing a health history questionnaire.
Subjects were 12-14 hours fasted upon arrival. Trained faculty and university student technicians measured body weight, height, and waist and hip (at the greatest girth of the gluteus) circumferences. BMI was calculated as weight in kilograms divided by height in meters squared. Waist to hip ratio (WHR) was calculated as waist circumference (cm) divided by hip circumference (cm). QT interval was measured from the earliest onset of the QRS complex to the end of the T wave in lead II. Measurements from five consecutive beats were averaged. Blood pressure was measured twice; blood was drawn (10 ml) and sent to a local laboratory for analyses.
An interviewer administered a questionnaire to determine estimated physical activity levels for adults and adolescents, respectively. These questionnaires determine the average hours per week over the past year spent in occupational and leisure physical activity (PA). Each occupational activity or leisure activity was weighted by an estimate of its relative intensity or metabolic equivalent (MET).
Subject data were blocked by the body mass index (BMI) for normal weight (BMI<25), overweight (BMI 25-29.99), and obesity (BMI>30), with children’s BMI values being adjusted for age and sex. ANOVA tests were run to determine if significant differences existed in QTc between BMI groups. Physical activity data were blocked according to subjects who engaged in low (0.0 - 9.9 MET-hr/week), medium (10.0 - 35. 0 MET-hr/week) and high (>35 MET-hr/week) PA and ANOVA analyses completed to determine if PA significantly affected QTc duration.
Results
- Significantly longer QTc and significantly higher systolic and diastolic blood pressure values and fasting blood glucose levels were found for obese subjects compared to normal-weight mothers and daughters. QTc was positively correlated with WHR, and SBP and DBP for mothers, but not daughters.
- The average physical activity level for 56 percent of the women and 73 percent of the girls was less than 3.9 MET-hours per week, which is lower than the Surgeon General’s recommendation of 7.5-15 MET-hours per week.
- There was an inverse association between self-reported physical activity and QTc for mothers and daughters, which reached statistical significance for the obese daughters.
Conclusion
These results indicate a positive association between obesity and long QTc and an inverse association between self reported PA and QTc duration. Consequently, otherwise healthy individuals with obesity are at an increased risk for acquiring LQTS and the associated malignant ventricular arrhythmias. LQTS can be identified via a resting electrocardiograph (ECG) tracing, yet it is not common practice to screen otherwise healthy obese individuals for these conditions.
Chronic aerobic exercise training may protect against LQTS, but, to our knowledge, no one has quantified the exercise intensity, duration or length of training period required to favorably affect the LQTS. Combined with other risk factor information, determining the effect of a controlled exercise intervention on LQTS may have positive implications for informing healthy lifestyle habits, especially for a population at risk for developing obesity and engaging in low levels of PA, such as African American women and their daughters.
The American Physiological Society (APS) is one of the world’s most prestigious organizations for physiological scientists. These researchers specialize in understanding the processes and functions underlying human health and disease. Founded in 1887 the Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals each year.
Contact: Donna Krupa
APS Newsroom: April 20-24, 2002
Morial Convention Center, New Orleans
Room: Level 2, Room B211
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