Changes in body mass index in 11-12-year-old children in Hawkes Bay, New Zealand (1989-2000)

OBJECTIVE: To describe and compare the body mass index (BMI; weight/height2) profile of 11-12-year-old children in Hawkes Bay, New Zealand in 1989 and 2000. To subsequently determine the prevalence of overweight and obesity at the two time points using international definitions. METHODOLOGY: As part of asthma prevalence studies in Hawkes Bay data on height, weight and ethnicity were collected from 871 school children in 1989, and 894 children in 2000 who reached 12 years of age during the year of testing. RESULTS: In the total study population the geometric mean BMI increased from 18.1 kg/m2 (95% CI 17.9; 18.3) in 1989 to 19.8 kg/m2 (95% CI 19.6; 20.0) in 2000, a relative increase of 9.2% (95% CI 7.6; 10.9), P < 0.001. Significant relative increases were found for males (9.0%: 95% CI 6.8; 11.3), females (9.3%: 95% CI 6.8; 11.8), Maori (7.6%: 95% CI 4.3; 11.1), European (9.1%: 95% CI 7.3; 11.0) and Pacific Island children (11.0%: 95% CI 2.2; 20.5). In 2000 20.9% of Hawkes Bay children were classified as overweight and 9.1% as obese. The risk of being overweight in 2000 was 2.2 times greater than the risk in 1989, and the risk of being obese was 3.8 times greater, with these problems more pronounced among Maori (overweight 24.7%, obese 15.3%) and Pacific Island (overweight 35.0%, obese 15.0%) than European (overweight: 18.2%, obese 5.7%) children. However, the risk of being overweight (RR = 3.0, 95% CI 2.2-4.0) or obese (RR = 8.3, 95% CI 3.0-23.3) in 2000 compared to 1989 was greater among European children. CONCLUSION: Higher percentages of Maori and Pacific Island children are overweight or obese compared to European, but in all ethnic groups there has been a statistically significant increase in mean BMI over an 11-year period. This increase reflects the trend observed in other developed countries and underlines childhood obesity as a major health problem in New Zealand.