[A national epidemiological survey on obesity of children under seven years of age in nine cities of China in 2016].

Objective: To investigate the prevalence and risk factors of obesity in 2016 and to determine secular trend of the prevalence between 1986 and 2016 among Chinese children under seven years of age.
Methods: Data of a total of 110 485 children from 1 month to 7 years of age were collected by stratified-clustered-random sampling method in the nine cities (including northern China (Beijing, Harbin, Xi'an), Central (Shanghai, Nanjing, Wuhan), Southern (Guangzhou, Fuzhou, Kunming)) from June to November in 2016. Overweight and obesity were defined by the weight for height of the American National Center for Health Statistics/World Health Organization (NCHS/WHO) reference and be over 10% as overweight and over 20% as obesity (20%-29% as mild, 30%-49% as moderate and over 50% as severe). The normal children were matched with obese children in sex, age and height in the case-control designs and the data were analyzed by χ(2) test and conditional Logistic regression model.
Results: (1) The overall overweight prevalence was 8.4% (9 317/110 485) with boys 8.4% (4 843/57 917) and girls 8.5% (4 474/52 568) and the overall obesity prevalence was 4.2% (4 712/110 485) with boys 4.9% (2 860/57 917) and girls 3.6% (1 852/52 568). The obesity prevalence was significantly different across age groups (χ(2)=3 777.586, P<0.01), the lowest 0.9% (144/16 380) (boys 1.1% (97/8 668), girls 0.6% (47/7 712)) at 1-<2 year and the highest 11.3% (1 248/11 072) (boys 14.0% (822/5 861), girls 8.2% (426/5 211)) at 6-<7 years. The overall obesity prevalence was 4.6% (2 534/54 970) for suburban rural children and 4.0% (2 178/55 515) for urban children. The overall obesity prevalence in northern, central and southern China was 4.7% (1 985/42 294), 4.4% (1 543/35 260) and 3.6% (1 184/32 931) respectively. The mild obesity prevalence was 2.8% (3 146/110 485) and the moderate 1.1% (1 272/110 485) and severe obesity 0.3% (294/110 485). (2) To ensure data comparability, the 2016 urban data were compared with the previous survey urban data. Compared with the 1986 and 2006 survey data, the obesity prevalence increased from 0.9% (660/71 420) and 3.8%(2 227/59 302) to 4.6% (1 341/29 054) for boys, from 0.9% (596/66 609) and 2.5%(1 323/53 643) to 3.1% (837/26 461) for girls. The increase in prevalence of obesity mainly appeared after 3 years of age. The obesity prevalence among north, central and south China increased from 1.8% (562/31 301) and 3.2% (1 137/35 439) to 4.2% (864/20 372), from 0.9% (464/52 138) and 3.9%(1 412/37 031) to 4.2% (764/18 485), from 0.4% (230/54 590) and 2.5% (1 001/40 475) to 3.4% (550/16 658) when compared with 1986 and 2006. (3) Multivariate Logistic regression analysis showed that high birth weight (odds ratio (OR)=1.559 (1.038-2.343), χ(2)=4.580, P<0.05), cesarean section (OR=1.651 (1.230-2.216), χ(2)=11.132, P<0.01), gestational diabetes (OR=3.364 (1.406-8.047), χ(2)=7.433, P<0.01), father overweight (OR=1.935 (1.417-2.642), χ(2)=17.267, P<0.01) or father obesity (OR=3.580 (2.304-5.561), χ(2)=32.196, P<0.01), mother overweight (OR=2.305 (1.611-3.298), χ(2)=20.854, P<0.01) or mother obesity (OR=5.232 (2.751-9.949), χ(2)=25.462, P<0.01), good appetite (OR=8.313 (5.385-12.833), χ(2)=91.403, P<0.01), eating fast (OR=6.359 (4.539-9.010), χ(2)=112.513, P<0.01), eating shortly before sleeping (OR=1.553 (1.113-2.166), χ(2)=6.707, P<0.01), long screen watching duration (2-<3 hours: OR=1.973 (1.423-2.736), χ(2)=16.594, P<0.01 or ≥3 hours: OR=2.275 (1.413-3.661), χ(2)=11.448, P<0.01), short night sleep duration (8-<9 h/day) (OR=1.600 (1.074-2.385), χ(2)=5.331, P<0.05), low education of mother (OR=1.589 (1.298-1.945), χ(2)=20.174, P<0.01) may be risk factors for children's obesity; moderate and excessive outdoor activities (e.g. running, jumping) may be protective factors against obesity (OR=0.540 (0.342-0.853), χ(2)=6.990, P<0.01). Conclusions: In recent ten years the rapidly increasing trend of children obesity has not been effectively curbed and there has been a new situation in the obesity prevalence of suburban rural children exceeding urban children. The key roles of mother in the early growth and development and family in the formation of good behavior habits of their children should be paid attention to, and family-based obesity prevention and control strategies for preschool children should be developed and improved to correct unhealthy family sharing environment and children's lifestyle.