Barbara Cliff

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Twelfth Annual Maternal and Child Health
Epidemiology Conference
Association between Body Mass Index and Waist
Circumference in Adolescents
Barbara Cliff Ph.D. Student, Interdisciplinary
Health Studies Western Michigan
University December 6, 2006
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Background

• Overweight and obesity are critical public health
  issues
• Overweight / fat adolescents are at high risk
• Diseases and premature death
• Obesity in adulthood
• Studies in adults suggest
• WC and BMI are highly correlated
• Body fatness is a strong indicator of health risk

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Body Mass Index (BMI)

• Measure that adjusts body weight for height
• Calculated as weight in kilograms divided by
  height in meters squared
• Based on universally accepted gender specific
  percentiles per age growth charts
• Most common measure due to ease
• Cannot distinguish between fat and fat free mass

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Waist Circumference (WC)

• Measure used to assess amount of abdominal fat
• Calculated in centimeters by measuring abdominal
  girth with a tape measure
• Not as commonly measured in adolescents
• No universally accepted cut-off points for
  adolescents
• May predict health risks beyond that predicted by
  BMI

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Purpose

• To examine the association of BMI and WC, as both
  continuous and categorical variables, among
  adolescents in the United States.

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Research Questions

• What is the association between BMI and WC in
  adolescents
• Among adolescents, do these associations differ
  by
• Gender
• Age
• Race / ethnicity

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Study

• Sample 2,176 U.S. adolescents, aged 12 19
• Secondary data analysis from National Health and
  Nutrition Examination Survey (NHANES)
• Used most recent two years (2003-2004)

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NHANES

• Nationally representative
• Conducted by the NCHS
• Cross-sectional examination surveys
• Stratified multistage probability sample

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Measures

• Body Mass Index
• Overweight (95th percentile)
• At Risk of Overweight ( 85th to 95th)
• Normal Weight (5th to 85th)
• Underweight (lt5th)
• Waist Circumference
• High Waist Value (90th percentile)
• Moderate Waist Value (75th to 90th)
• Normal Waist Value (lt75th)
• Li et al., 2006

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Analysis

• SPSS (version 14.0) with Complex Samples Add-On
  used for analysis
• Weighted to account for unequal probabilities
• Descriptive statistics
• Pearson correlation coefficients
• Bivariate regression analyses
• Cross tabulations/percent discordant for
  categorical variables

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Regression Analysis
Female
Male
l


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Adolescents by BMI (Percents)
Male Female (N1,119) (N1,057)
Overweight 20.5 20.2 At Risk of Overweight 18.3 18.0 Normal Weight 58.6 60.4 Underweight 2.6 1.5 100 100
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Adolescents by WC (Percents)
Male Female (N1,119) (N1,057)
High 16.4 22.3 Moderate 19.3 20.3 Normal 64.3 57.3 100 100
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Discordance in Male Subgroups
WC Normal High BMI At Risk At Risk
12-15 (n) N () Mexican-American (164) 2 (1.2) 4 (2.4) NH White (435) 9 (2.1) 12 (2.8) NH Black (648) 80 (9.4) 4 (0.5) 16-19 (n) Mexican-American (169) 8 (4.7) 2 (1.2) NH White (471) 15 (3.2) 3 (0.6) NH Black (816) 72 (8.8) 0 (0.0)
is of total for given age group and race/ethnicity No discordance identified in Normal WC/Overweight BMI or High WC/Normal Weight
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Discordance in Female Subgroups
WC Normal Normal High High BMI At Risk Overweight Normal At Risk
12-15 (n) N () Mexican-American (168) 2 (1.2) 0 1 (0.6) 11 (6.5) NH White (411) 3 (0.7) 0 0 27 (6.6) NH Black (724) 60 (8.3) 0 0 4 (0.6) 16-19 (n) Mexican-American (154) 3 (1.9) 0 2 (1.3) 13 (8.4) NH White (480) 18 (3.8) 0 15 (3.1) 15 (3.1) NH Black (732) 48 (6.6) 12 (1.6) 16 (2.2) 12 (1.6)
is of total for given age group and race/ethnicity
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Conclusions

• 38 of adolescent male female are at risk of
  overweight/overweight by BMI
• 36 of male adolescents 43 of females are of
  moderate or high WC
• BMI and WC are very highly correlated as
  continuous categorical variables
• Discordance identified in certain gender, age
  groups, racial / ethnic groups

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Conclusions

• Male
• Discordance in most normal WC/BMI at risk high
  WC/BMI at risk
• Greatest discordance (normal WC/at risk BMI) in
  NH Black, 12-15
• Concordance in normal WC/overweight BMI and high
  WC/normal BMI across all ages and race/ethnicity
• Female
• Discordance in all normal WC/BMI at risk high
  WC/BMI at risk
• Greatest discordance (high WC/at risk BMI) in
  Mexican-Americans, 16-19
• Slight discordance in normal WC/overweight by BMI
  in NH Black, 16-19, and high WC/normal BMI in
  Mexican-Americans, 12-15, and all race/ethnicity,
  16-19

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Discussion

• In adults
• Correlation between BMI WC
• High WC associated with higher health risks
• BMI WC are better indicators of weight status
  and together, are strong indicators of health
  risks
• In adolescents
• BMI alone is most common measure
• Strong association between BMI WC
• BMI WC may be a better indicator of weight
  status

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Strengths

• Large representative sample
• Trained interviewers
• High inter-rater reliability and validity
• Measures not self-reported reduced chance of
  bias

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Limitations

• Inability to link to health outcomes
• Undiagnosed confounders
• Socioeconomic status
• Family history
• Geographic locations

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Recommendations

• Establishment of universally accepted cutoff
  points for WC
• Consideration of BMI WC together to predict
  weight status in adolescents
• Exploration of the relationship between BMI, WC
  and health risks in adolescents