Hyperbolic weight-height correlation in children and adolescents: models and implications for obesity diagnosis

Many weight-height (Wt-Ht) models were proposed since the derivation of the "Quetelet Index", though their credibility remains elusive. This raises an interesting question about the presence of numerous Wt-Ht models and reveals that our knowledge about the Wt-Ht correlation is still far from its essence. We identified a strong linear correlation between Wt and Wt*Htc (c=-2[~]2), based on data from 359,049 participants aged 1 to 21 years, recruited from China, Japan, South Korea, Slovakia, the USA, and Bangladesh. Then, we established a statistically-robust Wt-Ht model, which is expressed as Wt=a+b*Wt*Htc (Eq. 1) or 1=a/Wt+b*Htc (Eq. 2), through linear regression. When c=1 or -1, Eq. 2 is a standard hyperbolic function, which proves that Wt is hyperbolically correlated with Ht. The coefficients a and b are sex-, age-, and geography-specific constants. As the exponent c approaches 0, the correlation between Wt and Wt*Htc, along with the standardized Wt-Ht index (sWHI) (a/Wt+b*Htc in Eq. 2), approaches 1. Further, we incorporated total fat to determine the implications of our model in obesity diagnosis. When c=1, the sWHI (a/Wt+b*Ht) is capable of screening abnormal body fat percentage (BFP) based on deviations from the Wt-Ht equilibrium (sWHI=1). BMI demonstrates advantages over other anthropometric indexes in screening abnormal BFP; nonetheless, their performances are largely similar. This is probably attributed to the strong linear correlation between Wt and Wt*Htc. Overall, the hyperbolic Wt-Ht model reveals the nature of Wt-Ht correlation and offers key insights into obesity diagnosis using anthropometric indexes.