Waist-to-height ratios in relation to BMI z-scores in three ethnic groups from a representative sample of New Zealand children aged 5–14 years

Waist-to-height ratio (WHtR) is purported to offer a simpler index of health risk than body mass index (BMI) in children as it requires no adjustment for age or sex. Little is known regarding the usefulness of WHtR in different ethnic groups. The aim of this study was to compare the WHtR cutpoints associated with BMI definitions of overweight and obesity in a nationally representative sample of New Zealand children. Height, weight and waist circumference were measured in 3006 children (51.5% male) aged 5–14 years (n=1107 Māori, n=985 Pacific and n=924 New Zealand European and Others (NZEO)). A WHtR >0.5 was more common in Pacific (43.4%) and Māori (33.1%) children than in NZEO children (20.8%, P<0.001), with 25.6% of children overall being above this cutoff. Although ethnicity influenced the relationship between BMI and WHtR (P<0.01), differences were clinically insignificant as illustrated by the similarity in WHtR values for a given BMI (WHtR of 0.47 in Māori, 0.46 in Pacific and 0.48 in European boys at the 85th BMI percentile). The present results suggest that having WHtR values >0.5 should be equally useful in evaluating cardiovascular health risks in groups of Māori, Pacific and NZEO children.