First reference curves of waist and hip circumferences in an Asian population of youths: CASPIAN study.

The Objective of the present study is to develop the first age- and gender-specific reference curves for waist and hip circumferences in an Asian population of youths. This cross-sectional population survey was conducted in 2003-04 on a nationally representative sample of 21111 school-students living in urban (84.6%) and rural (15.4%) areas of 23 provinces in Iran. After anthropometric measurements, smoothed reference curves for waist and hip circumference (WC, HiC) and waist-to-hip ratio (WHR) were developed by the LMS method. In both genders, WC and HiC percentile values increased with age. For girls, the 50th to 95th percentile curves for WC had a sharp increase between 8 and 13 years and 11-15 years, respectively, and began to plateau after this age, whereas for boys, these curves had a persistent and less sharp increase with age, until the age of 18 years. The WHR curves of girls decreased with age until 15 years and began to plateau thereafter, whereas for boys the 25th to 95th curves had a plateau pattern. Comparison of the current reference curves with the British ones showed that in boys, the 5th and 50th percentile curves were similar in both studies, but the 95th percentile curve of our study was higher than the British curves. For girls, the 5th percentile curves of both studies were similar, but the 50th and 95th percentile curves of our study were higher than the British ones. These curves represent the first childhood WC, HiC and WHR reference curves obtained in Asia. These curves can provide baseline data for analysis of time trends, as well as for international comparisons.