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Unadjusted BMI data mask substantial overweight, obesity in South Asian children in England

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November 9, 2017

Mohammed Hudda
Mohammed Hudda

Unadjusted BMI data in England underestimate the prevalence of overweight and obesity among the country’s South Asian children, particularly among those aged 10 to 11 years, and the numbers overestimate obesity prevalence among black children, according to a new analysis using ethnicity-specific BMI adjustments.

“The use of BMI to calculate overweight-obesity prevalence in English children of South Asian and black African origin is problematic, as it provides us with an inaccurate picture of the burden of disease we are facing,” Mohammed Hudda, MSc, a research fellow in medical statistics and epidemiology with the Population Health Research Institute at St. George’s, University of London, told Endocrine Today. “To effectively manage and prevent obesity, it is crucial to identify the current patterns accurately, which requires the use of ethnic-specific BMI adjustments.”

Hudda and colleagues analyzed data from the 2012-2013 National Child Measurement Program (NCMP) survey, an annual survey of the weights and heights of English children aged 4 to 5 years (n = 582, 899) and 10 to 11 years (n = 485,362), as directed by Public Health England (60% white, 5% black and 8% South Asian). The NCMP uses the British 1990 child growth reference population to assign each child a BMI centile, considering height, weight, sex and age. Children are classified as underweight ( second centile), healthy weight (> second centile, < 85th centile), overweight ( 85th centile, < 95th centile) or obese ( 95th centile). Children of Indian, Pakistani or Bangladeshi origin were considered to have South Asian ethnicity.

The researchers developed ethnicity-specific BMI adjustments for black and South Asian children, using pooled data from four recent studies that used the deuterium dilution reference method to assess fat free mass (and indirectly, fat mass) in black, South Asian and white children aged 4 to 12 years, they wrote. BMI adjustments were derived using sex-stratified regression models, ensuring that adjusted BMI values were associated with fat mass in the same way as in white children. Regression models were adjusted for ethnic group and age group.

“For South Asian children, single sex-specific positive BMI adjustments of +1.12 kg/m² for boys and +1.07 kg/m² for girls were applicable for all age-groups and body fatness levels,” the researchers wrote. “For black children, negative BMI adjustments were needed, which were modified by age and body fatness.”

Among white children, the combined overweight/obesity prevalence for boys and girls were 23% and 20.9%, respectively, among children aged 4 to 5 years, and 32.8% and 30.4%, respectively, among children aged 10 to 11 years.

Before adjustment, black children had a higher median BMI vs. white children for all age and sex groups (P < .0001). However, after ethnic-specific adjustment, black children aged 4 to 5 years (girls and boys) and black boys aged 10 to 11 years had a slightly lower median adjusted BMI, whereas black girls aged 10 to 11 years had a higher adjusted BMI when compared with white children (P < .0001). Compared with white children, the prevalence of overweight and obesity was slightly lower among black boys and girls aged 4 to 5 years and black boys aged 10 to 11 years, but black girls aged 10 to 11 years had a higher overweight and obesity prevalence vs. white children (P < .0001), according to researchers.

They observed varying patterns among South Asian children before adjustment. South Asian children aged 4 to 5 years had a lower median BMI vs. white children before adjustment, and the overweight and obesity prevalence was also lower among South Asian children aged 4 to 5 years when compared with white children. At age 10 to 11 years, South Asian boys had a higher median BMI vs. white children, but there was no marked difference in girls (P = .77), according to researchers. However, the overweight and obesity prevalence rates for both boys and girls were higher than for white children (P < .0001 for both). After adjustment, South Asian children (boys and girls), both at age 4 to 5 years and more so at age 10 to 11 years, had higher median BMI and higher overweight and obesity prevalence rates vs. white children (P < .0001 for all); more than half of older South Asian boys had overweight or obesity.

“The findings have very important clinical implications due to the elevated long-term risks of type 2 diabetes and cardiovascular diseases, which are observed among adults of South Asian and black African origins,” Hudda said. “It is, therefore, essential to ensure the accurate identification of overweight-obese children in these ethnic groups in order to concentrate efforts on the prevention of childhood obesity.”

The findings also draw attention to uncertainties in obesity prevalence rates at the local authority levels that have been reported annually by the NCMP, the researchers noted.

“Effective population-wide strategies for overweight/obesity prevention are, therefore, needed in all children, with a special emphasis on South Asian children and older black girls,” the researchers wrote. – by Regina Schaffer

For more information:

Mohammed Hudda, MSc, can be reached at the Population Health Research Institute, St George’s, University of London, Cranmer Terrace, London SW17 0RE; email: mhudda@sgul.ac.uk.

Disclosures: The authors report no relevant financial disclosures.