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Weight and cardiac disorders

Overweight and adolescents with obesity have similar heart risk

The researchers found no significant difference in heart rate variability between overweight and obese adolescents or between girls and boys

A study performed in Brazil by researchers from São Paulo State University (UNESP) suggests that overweight adolescents and adolescents with obesity have similar increased risks of developing heart disorders. The results of cardiovascular fitness tests with volunteers aged 10 to 17 were similar in both groups.

Supported by São Paulo Research Foundation (FAPESP), the results of the study, ‘Autonomic responses induced by aerobic submaximal exercise in obese and overweight adolescents’, were published in the journal Cardiology in the Young. The investigation also featured collaboration with colleagues at Kennesaw State University (USA) and Juazeiro do Norte College in Ceará (Brazil).

"Until recently, overweight in adolescence wasn't considered as important a risk as obesity for the development of cardiovascular disease. We found the risks to be similar in both cases," said Dr Vitor Engrácia Valenti, a professor at the UNESP campus in Marília and the principal investigator for the project.

The researchers divided 40 adolescents aged between 10 and 17 into two groups, each with ten boys and ten girls: an overweight group with BMI-for-age Z-scores of +1 or +2 and an obese group with Z-scores above +2. BMI is the ratio of weight to height. Z-scores indicate the number of standard deviations below or above the population mean.

The participants performed a moderate exercise protocol, which involved walking on a treadmill at a slope of 0 percent and required 70 percent of the maximum estimated heart rate for this age group.

Heart rate variability was measured before and after the exercise session to assess the speed of autonomic cardiac function recovery. Prolonged autonomic nervous system imbalances after physical exertion have been shown to increase the risk of an acute event and of future cardiovascular disease.

During the first few seconds of an exercise session, the parasympathetic nervous system decelerates cardiac function. One of the two main divisions of the autonomic nervous system, this system conserves energy by slowing the heart rate and relaxing the body in other ways. After 50-60 seconds, the sympathetic nervous system kicks in, stimulating activity such as increased heart rate via adrenalin release, that prepares the body to react to a stressful situation.

According to Valenti, studies published in recent years have shown that the longer after a period of exertion the autonomic nervous system takes to stabilize so that heart rate returns to normal, the greater the risk of cardiovascular or metabolic disease.

The researchers found no significant difference in heart rate variability between overweight and obese adolescents or between girls and boys.

"The mean autonomic nervous system variables were practically identical for both groups regardless of sex," said Valenti. "These findings suggest that overweight adolescents have the same predisposition or vulnerability as that of obese adolescents to cardiovascular diseases such as hypertension and heart failure, as well as to metabolic disorders such as diabetes, dyslipidaemia, and high levels of triglycerides and LDL cholesterol."

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