Objectives: While researchers are increasingly recognizing the importance of adjusting waist circumference (WC) for height, no standard has yet been established. In this study we contrast three standard methods for indexing WC by height (using height, root-height and height-squared) via comparisons with age-specific optimal indices. Study Design and Setting: Measurements from 722 male and 746 female Caucasian participants in the Fels Longitudinal Study were used. The three standard waist-circumference indices (as well as an optimal index) were determined for ages 2 through 18, and for every decade thereafter to 70 years of age. Pearson correlations were used to assess the suitability of all indices. Results: The three standard indices remain correlated with the original WC measures, though each was associ-ated with height at some ages. Waist-to-height ratio is suitable for some childhood ages (boys: 5 - 9, 13 - 16;girls: 4 - 7, 9, 11 - 14) but not for adult ages;Root-height works well mostly for older teenage children and adults but not in early childhood and adolescence;Height-squared is nowhere suitable. In both men and women, the optimal indexing factor ranged between root-height and height-squared in childhood, and is close to root-height in adulthood. Conclusions: No one index is most suitable, as WC indexed by root-height is suitable for use with measurements from teenage children and adults, while waist-to-height ratio is generally suitable for use in children. WC indexed by height-squared is nowhere suitable.
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