NICE waist-to-height ratio guidelines "to have a waist<0.5 of your height", are suitable for children but misleading for adolescents.

Background and aim: National Institutes of Clinical Excellence (NICE) "at-risk" guidelines (waist-to-height ratio (WC/HT) < 0.5) over penalizes shorter adults and fails to alert taller adults who may be at risk. The aim is to assess whether the "at-risk" guidelines recommended by NICE are appropriate for children, by assessing whether their WCs increase in proportion to their height, thus obeying the principle of "geometric similarity.".

Methods and results: Cross-sectional study including 11018 participants aged 7-17 years. We assessed whether the children's waist circumferences (WC) increased in proportion to their heights (HT) using the allometric power law, WC = a.HT^b. We also cross-tabulated children (7-13 yrs) and adolescents (14-17 yrs) by height categories (short<145 cm, average 145-175 cm, and tall>0.175 cm) to identify whether taller or shorter individuals were equally "at-risk" (WHTR>0.5). The power law identified children's height exponents was approximately 1 (geometrically similar), but older adolescents' height exponents were approximately 0.5. We also identified that the frequency of children "at-risk" was evenly spread across the 3 height groups. In contrast, shorter adolescents were more frequently "at-risk" compared with their taller peers.

Conclusions: NICE guidelines (WC/HT < 0.5) are suitable for, and fairly classify children (aged 7-12 years) "at-risk" irrespective of their height. In contrast, shorter adolescents are consistently more likely to be unfairly classified as "at-risk" compared with taller adolescents, i.e., NICE guidelines (WC/HT < 0.5) will unfairly classify many adolescents as being "at-risk", with shorter adolescents being consistently over-penalized compared with their taller peers who may well be lulled into a false sense of security.