[A national epidemiological survey on obesity of children under 7 years of age in nine cities of China, 2006].

OBJECTIVE: To examine the epidemiological features of prevalence and influencing factors on obesity of Chinese children from 1 month to 7 years of age in nine cities.
METHODS: Stratified-clustered-random sampling was used, and the sampling size was 112 945 persons. Overweight and obesity were defined by the weight for height of NCSH/WHO reference, being over 10% as overweight and over 20% as obesity. The normal children were matched with obese children by region, gender, age and height in the case-control designs,and the data were analyzed by multiple conditional Logistic regression model.
RESULTS: (1) The overall prevalence of overweight was 6.25%, 6.59% for boys and 5.88% for girls. The overall prevalence of obesity was 3.19%, 3.82% for boys and 2.48% for girls. The prevalence of obesity in different age groups was significantly different, 1.86% for 1 month to 1 year old, lower for 1 to 3 years old, higher again after 3 years of age and reached 7.02% for 6 - 7 years of age. There was a significant regional difference in prevalence, which in the central (3.97%) and northern (3.21%) regions was higher than that in the south (2.47%). Most of the obese children belonged to mild obesity. Severe obesity occurred mainly after 3 years of age, and the prevalence of severe obesity for boys was significantly higher than the girls, in the northern part it was higher than those in the other two parts. (2) As compared with the survey data in 1986 and 1996, the prevalence of obesity increased by 2.78 times in the past 20 years, and the annual incremental rate was 6.9%. The prevalence of obesity increased rapidly after 4 years of age and significant gender difference was seen. The higher prevalence shifted from the north to the central part of China. (3) Results of the Logistic regression indicated that appetite, eating speed, high maternal and paternal BMI, child caretaker, mode of delivery, main style of the outdoor activities, hours of watching TV, birth weight and duration of night time sleep were significantly related to obesity.
CONCLUSION: (1) During the past 20 years the prevalence of child obesity showed a fast increasing trend in China. Degrees of the increasing trend differed across gender and age groups and regions. Effective strategies for intervention on population should be stipulated. (2) Good appetite, fast eating, high BMI of parents, caesarean birth, high birth-weight and excess hours of watching TV were possibly associated with increased risk of obesity in childhood, and those children looked after by their parents, medium intensity outdoor exercise and sufficient night sleep were associated with decreased risk of obesity.