Waist Measurements Linked With Lipids, BP, in Youth

April 05, 2012

April 3, 2012 (Toronto, Ontario) The addition of waist measurements to body-mass index (BMI) can help further stratify young individuals who might have abnormal lipid and blood-pressure values, according to the results of a new study [1]. Investigators suggest that these waist measurements, including waist circumference and the waist-to-height ratio, should be included in the screening and assessment of overweight and obese adolescents.

"What we found was that once you categorize people as being normal weight, overweight, or obese, adding in waist circumference further increased the specification within those categories for the risk of cholesterol problems or blood-pressure issues," lead investigator Dr Brian McCrindle (Sick Children's Hospital, Toronto, ON) told heartwire .

The study, published online April 2, 2012 in the Archives of Pediatrics and Adolescent Medicine, is a population-based, cross-sectional analysis of 4884 ninth-grade students (14–15 years old) living in southern Ontario. BMI is currently the most widely used assessment of adiposity in adults and children, with age- and sex-specific values formulated by multiple organizations, including the Centers for Disease Control and Prevention (CDC) and the World Health Organization. To heartwire , McCrindle said BMI is not particularly accurate in identifying adiposity in high-school children, given its inability to distinguish between fat and fat-free mass.

"When you're looking at the relationship between overweight and obesity and health and risk factors, it's not just how fat you are but it's also the distribution pattern of the fat as well," said McCrindle. "For people who tend to carry more fat around their waist, that fat leads to a much greater risk of health problems than fat in other locations."

McCrindle said one of the reasons his group conducted the study was to address discrepancies between the Canadian and US guidelines on the use of waist-circumference measurements for risk assessment in pediatric patient populations. For the evaluation and management of overweight and obese children, adolescents, and adults, the 2006 Canadian guidelines recommend the use of waist-circumference measurements, but the 2007 joint statement from the American Medical Association, CDC, and the American Academy of Pediatrics believes the waist-circumference measures are difficult to standardize and have uncertain normal values. On the whole, the US guidelines do not believe there is sufficient evidence to include waist circumference as part of risk assessment.

Worsening Lipid and Blood Pressure

In this new study, the associations between blood pressure and lipid profile and measures of adiposity (BMI alone, BMI/waist-circumference percentiles, and BMI/waist-to-height ratio) were statistically significant. There were no observed differences in the performance of the clinical models using BMI alone, BMI and waist-circumference percentiles, and BMI and the waist-to-height ratio. In multivariate regression models that adjusted for age and sex, increasing waist-to-height ratios were significantly associated with worsening lipid profiles across BMI strata, with the strongest association observed in obese patients. Among obese patients, an increased waist-to-height ratio was associated with a significantly increased risk of hypertension compared with subjects with normal waist measurements.

McCrindle said that because adolescents might have an elevated BMI given their muscle mass, waist-circumference measurements, including the easy-to-calculate waist-to-height ratio, can help clinicians stratify individuals who might be at risk of cardiovascular disease in later adulthood based on elevated cholesterol and blood-pressure abnormalities. Not every health problem in the world is related to obesity, and some of these kids might have genetic abnormalities that cause elevations in cholesterol or blood pressure, said McCrindle. It is for this reason that the new pediatric guidelines recommend integrated cardiovascular screening at age 10.

"These risk factors don't necessarily cause any symptoms, and they usually don't cause any manifest disease until adulthood," said McCrindle. "The opportunity for preventing the adult disease really lies in the pediatric age groups, so you need to screen them if you want to realize the opportunity for primary prevention."

The results of the study also provide some justification for using the waist-to-height ratio based on its performance and ease of use. A ratio of 0.50 or less is considered normal, while 0.60 is considered abnormal. McCrindle said the ratio worked just as well as waist circumference in terms of mediating the risk of BMI in this study and has easy cut points that can help physicians identify potentially at-risk adolescents.

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