How does maturity adjustment influence the estimates of overweight prevalence in adolescents from different countries using an international reference?

OBJECTIVE: To investigate the effect of adjusting for differences in timing of maturation when assessing overweight prevalence among adolescents in different populations by using an international reference recommended by the WHO.

DESIGN: Cross-sectional, comparative study in three large samples from China, Russia and the United States.

SUBJECTS: A total of 2014 American, 1316 Chinese and 744 Russian non-pregnant adolescent girls aged 10-18 y.

MEASUREMENTS: Data on body weight, height, menarcheal status and age at menarche (AAM) were collected. Overweight was defined as age-sex-specific body mass index (BMI) greater than the 85th percentiles from the US NHANES I data (collected in 1971-1974), which is recommended by the WHO for international use. Maturity adjustments were made using population differences in median age at menarche (MAM), calculated using the status quo method. MAM was 12.8 in the WHO reference population, 13.7 in China, 13.2 in Russia, and 12.6 in the US (NHANES III data). Maturation age-matched BMI cut-offs were used to compute the adjusted prevalence. We also compared population-adjusted results with individually adjusted results in post-menarcheal American girls (based on each girl's AAM) and in pre-menarcheal girls (based on breast stage).

RESULTS: Maturity adjustment increased the estimated prevalence of overweight in China and Russia where girls mature later than the reference population, and decreased it in the NHANES III sample. The unadjusted and adjusted prevalence was 3.5 vs 4.9% in the China sample, 8.3 vs 9.7% in Russia, and 29.2 vs 28.0% in the US. The adjustment had a greater effect in younger adolescent girls (10-13 y) than in older girls (14-18 y). In general, we found a good agreement between the population and individual adjustments. Viewing the individual adjustment as a 'gold standard', the population method has a high sensitivity and specificity.

CONCLUSION: This is the first study to assess WHO recommendations for maturation adjustment when estimating overweight prevalence in different countries. While the overall effects of adjustment are small, maturation status should be considered, particularly when assessing young adolescents, and populations with markedly different timing of maturation relative to the international reference. Population-based adjustment is useful and practical in situations where individual maturity data are not available.