Obesity is widely recognised to be a major public health concern, and inequalities in body fat distribution are of great current interest. This bulletin uses data from the 2002/03 New Zealand Health Survey to analyse ethnic and gender variations in socio-economic gradients in body fat distribution, using a range of measures of body fat and of socio-economic position.
The magnitude and even the direction of the socio-economic gradients in body mass index and waist circumference were found to vary between males and females and between Māori and non Māori ethnic groups.
These differences may reflect differential timing of the obesity epidemic in these population groups, cultural or behavioural differences, and / or differential lifecourse effects. If so, the ethnic and gender differences in the gradients may be expected to change over time.
These inequalities, and any future trends in these inequalities, may need to be taken into account when designing or evaluating policies under the Healthy Eating Healthy Action initiative.
Purpose
The aim of this analysis was to quantify ethnic and gender variation in the socioeconomic gradient in body fat in New Zealand, using different measures of socioeconomic position and body fat. Understanding such variation, and trends in this variation over time, may be relevant in formulating and evaluating policies and interventions under the Ministry’s Healthy Eating – Healthy Action initiative (Ministry ofHealth 2004b).
Methodology
The 2002/03 New Zealand Health Survey was used to derive kernel-smoothed estimates of the population’s body mass index (BMI) and waist circumference (WC) distributions. The percentiles of these distributions were then used to create Tukey mean–difference plots to graphically analyse the difference in body fat distributions between socioeconomic groups, stratified by Māori and non-Māori ethnicity and by gender. Age confounding was adjusted for by direct standardisation. Three different measures of socioeconomic position (SEP) were used: educational qualifications (individual-level measure), household income (household-level measure) and New Zealand Deprivation Index (neighbourhood-level measure).
Key Results
Overall, in 2002/03 both BMI and WC distributions were strongly associated with SEP, whether measured at the individual, household or neighbourhood level. Furthermore, the association was similar in direction and magnitude for both markers of body fat, with the inverse gradient increasing at higher BMI or WC percentiles. However, the association was modified by both gender and ethnicity. Non-Māori females showed a strong inverse socioeconomic gradient for BMI and WC, non-Māori males a much shallower inverse gradient, Māori females little if any relationship, and Māori males a moderately strong direct gradient (ie, among Māori males, higher SEP was associated with larger BMI or WC).