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The Prevalence of obesity in British children – is BMI telling us the whole story?

The Prevalence of obesity in British children – is BMI telling us the whole story?. Dr. David McCarthy RNutr Institute of Health Research & Policy London Metropolitan University 17 th February 2005. Body Mass Index (BMI). in adults - affected minimally by age

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The Prevalence of obesity in British children – is BMI telling us the whole story?

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  1. The Prevalence of obesity in British children – is BMI telling us the whole story? Dr. David McCarthy RNutr Institute of Health Research & Policy London Metropolitan University 17th February 2005

  2. Body Mass Index (BMI) • in adults - affected minimally by age • popular, quick, use fixed cut-off points • in children - greatly affected by age

  3. Early childhood prevalence in the UK • Obese 17% (BMI >95th centile) • Overweight 31% (BMI >85th centile) • Source: Reilly et al. 1999 BMJ319: 1039 • 2-5 year olds

  4. Drawbacks of BMI in children • Age-dependent • Correlates with both fat mass and fat-free mass • Low sensitivity • no indication of body fat distribution • Cannot identify secular trends

  5. Correlation of BMI with Fat Mass (kg) 16-18 year olds r2= 0.763, P<0.0001

  6. Correlation of BMI with Fat Free Mass (kg) 16-18 year olds r2 = 0.514, P<0.0001

  7. Assessment requirements in children • Simple measurement technique • Strongly related to morbidity or risk (CHD) • Biological/clinical definition • Avoid misclassification

  8. Central body fat accumulation in children • Intra-abdominal adipose tissue • Subcutaneous abdominal adipose tissue • assessed by circumference and skinfold measurements

  9. Is waist circumference in children linked to risk? • WC related to an atherogenic lipid profile in 12-14 yo (Flodmark et al. 1994) • WC related to adverse insulin levels in 5-17 yo (Bogalusa Heart Study, Freeman et al. 1999)

  10. Waist circumference and blood pressure • Jarrett, McCarthy et al. (unpublished observations in 4 and 5 year olds)

  11. The Metabolic Syndrome

  12. Waist circumference measurement Midway between the 10th rib and the iliac crest WHO standard method Used by : McCarthy et al. 2000 Freedman et al. 1999 Moreno et al. 1999

  13. Waist circumference measurement continued. At the level of the umbilicus Used for the waist circumference percentiles in Italian children, Zanolli et al. 1996

  14. UK children's waist circumference centile study • 8355 children • aged 5-17 years • mean and SD for waist circumference • smoothed percentile curves constructed using the LMS method (Cole 1990)

  15. Development of WC centile charts for the UK children n, 8355 McCarthy et al. 2001, EJCN

  16. Boys 3-17 y © D.McCarthy2001

  17. Girls 3-17 y © D.McCarthy2001

  18. Waist circumference vs BMI Boys aged 6.0-6.99 y p<0.01 r2=0.689 n=349 (cm)

  19. Waist circumference vs BMI Girls aged 6.0-6.99 y p<0.01 r2=0.716 n=400 (cm)

  20. BMI-WC relationship Subject Age BMI WC BMI %ile WC %ile (y) (cm) A 7.7 15.2 48 ~50th <9th B 7.5 15.3 65 ~50th >98th C 7.1 19.1 53 >91st ~50th D 7.1 20.0 67 >98th >99.6th

  21. Has upper body fatness increased in UK children? Comparison of data collected 10 and 20 years apart BSI and NDN surveys Children aged 11-16 years

  22. NDNS boys NDNS girls BSI boys BSI girls McCarthy et al. 2003. BMJ326: 624

  23. NDNS girls NDNS boys BSI girls BSI boys McCarthy et al. 2003. BMJ326: 624

  24. Changes over 10-20 years in overweight and obesity based on BMI and waist circumference in British children aged 11-16 years. Values are % exceeding 91st centile (98th centile) % prevalence of overweight % change (obesity) over time BSI 1977/87 NDNS 1997 Male Female Male Female Male Female BMI 7.7 5.9 20.6 17.3 12.9 11.4 (3.3) (1.6) (10.0) (8.3) (6.8) (6.6) WC 8.7 8.8 28.5 38.1 1 9.8 29.3 (3.3) (3.1) (13.8) (17.1) (10.7) (14.5) McCarthy et al. 2003. BMJ326: 624

  25. Is this also seen in younger children? Comparison of WC and BMI in children aged 2-5 years from the ALSPAC study with those in the BSI survey McCarthy et al. 2005. Int J Obesity29: 157-162

  26. Key findings from ALSPAC study • Mean WC greater in contemporary children • Increases greater in girls • Mean BMI slightly (but significantly) higher • Proportional increase in WC exceeded that for BMI

  27. Causative factors to consider – TV viewing • displaces physical activity • Increased energy consumption • Role of advertising • Reduced resting metabolism

  28. Causative factors to consider – eating habits and energy intake

  29. Energy dense drinks • Cola – 11% sugar • Orange juice – 10% sugar • Juices perceived as being ‘healthier’

  30. Conclusions and recommendations • Several limitations of BMI use in children • Excess upper body fatness more closely linked to morbidity than general fatness • WC better than BMI in identifying obesity-related risk in children • WC measurement should be taken routinely in obesity assessment in children • More research needed into excess upper body fat accumulation in childhood

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