To the Editor: As part of a large, national nutrition study, height and weight were measured among 4441 students from 38 schools randomly selected from lists of all state and territory schools in Australia in 2000. Public, private and Catholic schools, in both rural and urban areas, were represented.

Schools were categorised as being of low or middle/high socioeconomic status (SES),1 based on direct measurement of parental income. Parental consent was obtained, and the study was approved by the University of Sydney Ethics Committee and all state departments of education.

Overweight and obesity, as defined by an international standard definition,2 were identified in 17.3% and 6.4% of participants, respectively. These characteristics showed a trend towards greater prevalence among students from low-SES backgrounds compared with those from middle/high-SES backgrounds for the total group (19% v 16.8% overweight [P = 0.09]; 8.9% v 5.8% obese [P = 0.02]), females (19.7% v 17.2% overweight [P = 0.2]; 6.9% v 6.2% obese [P = 0.56]), and males (18.5% v 16.3% overweight [P = 0.23]; 9% v 5.5% obese [P = 0.003]), although not all differences were statistically significant.

After controlling for SES differences in age and height, mean body mass index (BMI) was significantly higher among low-SES than middle/high-SES participants for the total group (20.3 kg/m2 [95% CI, 20.1–20.5 kg/m2] v 19.7 kg/m2 [95% CI, 19.6–19.9 kg/m2]; P < 0.001), females (20.4 kg/m2 [95% CI, 20.1–20.7 kg/m2] v 19.8 kg/m2 [95% CI, 19.6–19.9 kg/m2]; P < 0.001), and males (20.2 kg/m2 [95% CI, 20.0–20.5 kg/m2] v 19.6 kg/m2 [95% CI, 19.5–19.8 kg/m2]; P < 0.001). A breakdown of results by SES, sex and school level is shown in the Box.

Low-SES primary school children were also 1–2 cm shorter, on average, than middle/high-SES primary school children (boys: mean 141.5 cm [95% CI, 140.6–142.5 cm] v 143.5 cm [95% CI, 143.0–144.0], P < 0.001; girls: mean 141.0 cm [95% CI, 140.8–142.6 cm] v 143.3 cm [95% CI, 142.5–143.6 cm], P = 0.01).

The average proportions of overweight and obese children and adolescents in the study were similar to those found in other Australian studies.3-5

The results suggest that SES is a factor in the development of overweight and obesity among Australian school children. This may be a relatively recent trend, as these data were obtained in late 2000. Low SES in children may also be associated with nutritional deprivation and height retardation. Further research should clarify these relationships among children from low, middle and high SES backgrounds, as well as examining the combined impact of both SES and ethnicity.