David Mccarthy

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The Use of the Body Mass

Index in Under 18 year oldsDr. David McCarthy RNutr

Institute ofHealth Research & Policy

London Metropolitan University28th March 2004


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Body Mass Index (BMI)

in adults - affected minimally by age

popular, quick, use fixed cut-off points

in children - greatly affected by age


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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


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BMI

40302010

FatMas

s(kg)

40

30

20

10

0

Correlation of BMI with Fat Mass (kg)

r2= 0.763, P


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Cut-off points

US 85th

and 95th

centiles UK 91st and 98th centiles

IOTF centiles relating to BMI of 25and 30 at age 18 years


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Childhood prevalence

in the UK

Obese 17% (BMI >95th centile)

Overweight 31% (BMI >85th centile)

Source: Reilly et al. 1999


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Waist circumference

in adults

Indicator of intraabdominal fat

related to risk for NIDDM,hypertension and CVD

waist:hip and waist:height ratios


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Is waist circumference in

children linked to risk?

WC related to an adverse atherogenic

lipoprotein profile in 12-14 year olds(Flodmark et al. 1994)

WC related to adverse insulin

concentration in 5-17 year olds(Bogalusa Heart Study, Freeman et al. 1999)


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Waist circumference

and blood pressure

Jarrett, McCarthy et al. (unpublished

observations, 2002), 4 and 5 year olds)


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The Metabolic Syndrome


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WC percentile charts

in children

Italian children (Zannolli & Morgese

1996)

Spanish children (Moreno et al. 1999)

Cuban children (Martinez et al. 1994)

British children (McCarthy et al. 2000)


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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


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Waist circumference measurementcontinued.

At the level of the umbilicus

Used for the waist circumference

percentiles in Italian children,

Zanolli et al. 1996


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UK children's study

8355 children aged 5-17 years

mean and SD for waistcircumference

smoothed percentile curvesconstructed using the LMS method(Cole 1990)


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4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Age (years)

40

50

60

70

80

Waistcircumference

(cm)

Boys

Girls

Waist in children

n, 8355 McCarthy et al. 2001, EJCN

Development of WC centile charts for the UK children


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What about clothing effects? Preferable to measure

over skin

need to take account of

vest, T-shirt or school

shirt

subtract 0.5 cm from

reading

problem in measuringover tunics

22Waist circumference vs BMI


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Waist Girth WsGr

70605040

BMI

22

20

18

16

14

12

Boys aged 6.0-6.99 y

p


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Waist Girth WsGr

8070605040

BMI

24

22

20

18

16

14

12

10

Girls aged 6.0-6.99 y

p


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BMI-WC relationship

Subject Age BMI WC BMI %ile WC %ile

(y) (cm)

A 7.7 15.2 48 ~50th 98th

C 7.1 19.1 53 >91st ~50th

D 7.1 20.0 67 >98th >99.6th


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Has upper body fatness

increased in British children?

Comparison of data collected10 and 20 years apart

BSI and NDN surveys


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Ch 10 20 i BMI d i t


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Changes over 10-20 years in mean BMI and waist

circumference in British children aged 11-16 years.

Mean SD Score (SD) Mean increase

over time (SE)

BSI 1977/87 NDNS 1997

Male Female Male Female Male Female

BMI -0.05 -0.15 0.42 0.38 0.47 0.53

(1.02) (0.99) (1.13) (1.09) (0.06) (0.06)

WC 0.00 0.00 0.84 1.02 0.84 1.02

(0.99) (1.00) (1.02) (1.33) (0.06) (0.06)

McCarthy et al. 2003. BMJ326: 624


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How should I use the WC

percentile charts?

In conjunction with BMI centile charts

as a second line point of reference for

referral

routinely

epidemiology

research


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Further issues

Cut-off points yet to be linked to risk or

Fat Mass

What effect does measurement error

have upon validity of WC percentiles?

Relationship between BMI and WC

centile


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Conclusions

Waist circumference important in children

Simple technique

WC correlates with risk factors for CHD

further work required on validation of

technique

other countries could begin to develop WC

percentiles in their childhood population


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Genetics Prenatal diet

Leg length?

Infant feeding

Current diet

Physical

activity

central obesity

Catch-up

growth


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Acknowledgements

Karen Jarrett

Adam Collins

Prof. Tim ColeSandra Ellis

Pauline Emmett

Jean Golding andthe ALSPAC

team

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