Secular trends and urban-rural disparities in the median age at menarche among Chinese han girls from 1985 to 2019.

BACKGROUND: Menarche is a substantial milestone of female puberty. Timing of age at menarche is considered the key to understanding the potential linkages with women's health outcomes later in life. This study aimed to explore the secular trends and urban‒rural disparities in the median age at menarche among Chinese Han girls from 1985 to 2019. METHODS: Data were extracted from the 1985, 1995, 2005, 2014, and 2019 Chinese National Surveys on Students' Constitution and Health, which were nationally representative cross-sectional studies, and a total of 173,535 Han girls aged 9-18 years were examined. Girls were asked whether menarche had occurred. The median age at menarche was estimated by probit analysis. Z tests were used to compare the differences between survey years and between urban and rural areas. RESULTS: The median age at menarche among Chinese Han girls decreased from 13.37 years in 1985 to 12.00 years in 2019, and the overall decrease was more significant in rural areas (1.77 years) than in urban areas (0.99 years). The average five-year change in the decrease in the median age at menarche showed an accelerating and then slowing pace; and it was observed similarly in both urban and rural areas. The urban‒rural disparities shrank from 0.64 years in 1985 to 0.44 years in 1995, then to 0.27 years in 2005, 0.24 years in 2014, and finally to - 0.14 years in 2019. CONCLUSIONS: The median age at menarche among Chinese Han girls continued to decline from 1985 to 2019 but at a slowing pace in the last five years. Urban‒rural disparities gradually narrowed. Sexual and reproductive health education and interventions to prevent the decline in the age of menarche are needed, especially in rural areas.

Reducing Anemia Among School-Aged Children in China by Eliminating the Geographic Disparity and Ameliorating Stunting: Evidence From a National Survey.

Background: The aim of this study was to assess the geographic disparity in anemia and whether stunting was associated with anemia in different geographic groups among school-aged children in China. Methods: 71,129 Han children aged 7, 9, 12, and 14 years old were extracted from the 2014 cycle of Chinese National Surveys on Children Constitution and Health. Anemia, anemia severity, and stunting were defined according to WHO definitions. Binary logistic regression models were used to estimate the association between anemia and stunting in different geographic groups. Results: The prevalence of anemia was significantly higher in girls (10.8%) than boys (7.0%). The highest anemia prevalence was in Group VII (lower class/rural, 12.0%). A moderate/severe prevalence of anemia was concentrated in Group VII and Group VIII (western/lower class/rural) for both sexes. The prevalence of anemia was higher in stunting boys than non-stunting boys in Group IV (lower class/city, χ2 = 12.78, P = 0.002) and Group VII (χ2 = 6.21, P = 0.018), while for girls, it was higher in stunting girls than their non-stunting peers only in Group II (upper class/large city, χ2 = 4.57, P = 0.046). Logistic regression showed that the stunting children have 30% higher risk of anemia than non-stunting children after adjustment for age, sex and school (OR = 1.30, 95% CI: 1.05-1.60). Conclusion: A significant geographic disparity and an association between anemia and stunting among specific groups of school-aged children in China was demonstrated. Consequently, eliminating the geographic disparity and ameliorating stunting might contribute to the improvement of Chinese children's anemia. Specific guidelines and interventions are needed, especially for adolescent girls and the groups with serious anemia burden.

[Secular trends of height among Chinese students aged 17 in 18 ethnic minorities from 1985 to 2010].

OBJECTIVE: To analyze the secular trends of height among Chinese students aged 17 in different ethnic minorities from 1985 to 2010. METHODS: A total of 18 Chinese ethnic minorities' students, including Mongolian, Hui, Uygur, Zhuang, Korean, Tibetan, Miao, Buyi, Dong, Bai, Tujia, Hani, Dai, Lisu, Wa, Nakhi, Tu and Qiang as subjects were sampled from the 1985, 1995, 2000, 2005 and 2010 Chinese National Surveys on Students' Constitution and Health. The heights of 17 years old people by gender in various ethnic minorities were analyzed and compared. RESULTS: From 1985 to 2010, the increments of adult heights increased significantly in many ethnic minorities' boys. In 2010, the average height of boys aged 17 years in each minority group was higher than 162 cm and was higher than 170 cm among boys from Hui, Mongolian and Korean groups. The ethnics with height growth rates of more than 2 cm per decade in boys were Hui (2.64 cm/decade) and Dong (2.05 cm/decade) and the ethnics with height growth rates of more than 1 cm per decade were Korean (1.99 cm/decade), Tibetan (1.90 cm/decade), Hani (1.80 cm/decade) and the other 9 minority groups. The average height of girls aged 17 years in each minority group was higher than 150 cm in 2010. The heights showed an upward trend in 15 minority groups, but with different degrees. The ethnics with height growth rates of more than 1 cm per decade were Hui (1.56 cm/decade) and Korean (1.29 cm/decade). The increments that were significant between 1985 and 2010 were Hui (3.89 cm), Korean (3.23 cm), Dong (2.35 cm) and the other 6 minority groups (P<0.05). CONCLUSION: Our data suggest that the increments of adult heights may reflect the secular growth change in the major minority groups during the past 25 years, but there was an obvious disequilibrium among various ethnic minorities. We should pay more attention to the minority groups with poor growth and give them more help. Meanwhile, we should also pay attention to the negative effects of the secular growth trend on those minority groups with fast increasing adult height.

[Current situation and comparison of age at menarche in 26 ethnic minority groups in Chinese girls in 2010].

OBJECTIVE: To analyze the current situation of age at menarche (AAM) in Chinese ethnic minority girls aged 9-18 years, and compare the AAM with that of Chinese Han girls from the same province or autonomous region. METHODS: Probit analyses were used to calculate the AAM in various ethnic minority groups of Chinese girls who participated in 2010 National Physical Fitness and Health Surveillance. The sample size of ethnic minority girls was 31 711, and the ethnic minorities were Mongolian, Hui, Tibetan, Uighur, Miao, Yi, Zhuang, Buyi, Korean, Dong, Yao, Bai, Tujia, Hani, Kazak, Dai, Li, Lisu, Wa, Shui, Dongxiang, Naxi, Kirgiz, Tu, Qiang and Sala. The local Han girls to compare with the AAM were also surveyed in 2010 National Physical Fitness and Health Surveillance. RESULTS: In the 13-year-old group, the percentage of menarche in Sala was the lowest (32.17%), while that in Korean was the highest (93.23%). At the age of 18, 99.60% ethnic minority girls appeared menstruating. The AAM of the top 3 ethnic minority groups were Korean (11.79 years), Mongolian (12.44 years) and Zhuang (12.52 years); and the last 3 ethnic minority groups were Dongxiang (14.36 years), Sala (14.32 years) and Shui (14.02 years). The AAM in Korean was 0.93 years earlier than that of the Han girls from Jilin province; the AAM in Mongolian was 0.14 years earlier than that of the Han girls from Neimenggu autonomous region; the AAM in Naxi and Qiang was close to that of the Han girls in the same province (region) (P>0.05); and the AAM in Hui, Uighur, Miao, Yi, Zhuang, Buyi, Dong, Yao, Bai, Tujia, Hani, Kazak, Dai, Li, Lisu, Wa, Shui, Dongxiang, Kirgiz, Tu, and Sala was later than that of the Han girls in the same province (region). The cluster analysis indicated that the 26 ethnic minority groups could be classified as three groups: Korean were classified into the earlier age group of AAM; Dongxiang, Sala, Uighur, Yi and Shui belonged to the later age group of AAM; and the other 20 ethnic minority groups were into the middle age group of AAM. CONCLUSION: There was a large variation among different ethnic minority groups in China. The AAM was earlier in Korean, and Mongolian, compared with the local Han girls, and the AAM in other ethnic minority groups was the same or later compared with the local Han girls.

[Analysis of influencing factors on physical endurance of Chinese primary and middle school students aged 10 to 17].

OBJECTIVE: To explore the influencing factors on physical endurance among Chinese primary and middle school students aged 10-17. METHODS: Data was used from "2010 National Physical Fitness and Health Surveillance", from which 68 458 primary and middle school students with complete information were selected. Good physical endurance was defined as endurance running time ≤ P 25 of same gender and age, poor physical endurance as ≥ P 75 of same gender and age. Difference of endurance running time in different physical endurance groups was compared; chi-square test, logistic regression and multiple level model were used to analyze influence of region, BMI, diet, exercise and exercise willingness on physical endurance. RESULTS: There were 34 293 (50.0%) students of good physical endurance and 34 219 (50.0%) ones of poor physical endurance in 68 458 subjects. Percentage of good physical endurance was 53.8% (18 285/33 996) in rural students, higher than urban ones (46.3% (15 954/34 462)) (χ(2) = 384.16, P < 0.01). Percentage of good physical endurance was 12.2% (448/3660) in obese students, lower than normal (55.2% (28 183/51 028)), overweight (29.3% (2012/6874)) and emaciated ones (52.1% (3596/6896)) (χ(2) = 3840.08, P < 0.01). Percentage of good physical endurance was 52.5% (25 534/48 679) in students having breakfast everyday, higher than ones never having breakfast or 1-2 times per week (41.3% (3209/7768))(χ(2) = 438.31, P < 0.01). Percentage of good physical endurance was 51.7% (11 580/22 379) in students having milk everyday, slightly higher than ones never or sometimes having milk (49.2% (22 659/46 079)) (χ(2) = 39.84, P < 0.01). Percentage of good physical endurance was 55.3% (18 961/34 314) in students with adequate physical education class, higher than ones with inadequate class (44.7% (15 278/34 144)) (χ(2) = 756.41, P < 0.01). Percentage of good physical endurance was 58.6% (9484/16 195) in students with one hour exercise or more per day, higher than ones with less than one hour exercise (47.4% (24 755/52 263)) (χ(2) = 619.82, P < 0.01). Percentage of good physical endurance was 60.1% (19 287/32 118) in students who were "very willing" to take part in endurance running, higher than "generally willing" ones (45.4% (10 569/23 272)) and "not willing" ones (33.5% (4383/13 068)) (χ(2) = 2909.61, P < 0.01). Multiple level analysis revealed that risk of poor physical endurance was lower in rural students (OR = 0.80, 95%CI: 0.77-0.82) than urban ones. Risk in emaciated students (OR = 1.11, 95%CI: 1.05-1.17), overweight students (OR = 2.69, 95%CI: 2.55-2.85) and obese students (OR = 7.71, 95%CI: 6.97-8.52) was higher than normal ones. Concerning diet, risk of poor physical endurance in students never having breakfast or once to twice per week was highest (OR = 1.20, 95%CI: 1.13-1.26), followed by students having breakfast three to five times per week (OR = 1.13, 95%CI: 1.08-1.18); risk in students having one bag of milk per day was higher (OR = 1.09, 95%CI: 1.02-1.17) than ones having two bags. Concerning exercise, risk of poor physical endurance in students with inadequate physical education class (OR = 1.20, 95%CI: 1.13-1.26) and less than one hour exercise per day (OR = 1.34, 95%CI: 1.29-1.40) was higher than ones with adequate physical education class and one hour exercise or more respectively. Risk of poor physical endurance in students who were "generally willing" (OR = 1.67, 95%CI: 1.61-1.73) and "not willing" (OR = 2.72, 95%CI: 2.60-2.85) to take part in endurance running was higher than "very willing" ones. CONCLUSION: Urban and rural residence, BMI, breakfast, milk, physical education class, exercise time and exercise willingness were related to primary and middle school students'physical endurance.

[Association between early menarche and physical fitness among adolescent girls in China].

OBJECTIVE: To explore the association between early menarche and physical fitness among adolescent girls in China. METHODS: Research material was selected from the data of "2010 National Physical Fitness and Health Survey". Probability unit regression method was used to calculate the age of 10th percentile at menarche and menarche age before the 10th percentile was defined as early menarche(9.0-11.6 years old). A total of 1072 girls with early menarche were selected. Each girl with early menarche was matched with one girl from the same urban or rural locations who hadn't achieved menarche with the age difference less than 0.1 years. A total of 1072 girls without menarche were selected. Indicators of physical fitness included 50 m running, standing broad jump, 50 m×8 shuttle running and sit-ups. Differences of physical fitness between early menarche and without menarche were analyzed using t test stratified by age and urban/rural area. The multilevel models of single dependent variable and multiple dependent variables were used to analyze association between early menarche and physical fitness. RESULTS: A total of 2144 students were put in this research. Among girls (11.0-11.6 years old) in urban areas, 50 m running, standing broad jump and sit-ups was (9.78 ± 0.85) s, (153.81 ± 18.59) cm, and 27.79 ± 10.25, respectively for those with early menarche, while in girls without menarche was (10.01 ± 0.90) s, (149.71 ± 18.72) cm and 26.28 ± 10.11, respectively. There were significant differences between two groups on all above variables (t values were 4.02, 3.43 and 2.31, respectively with all P values <0.01). Among girls in rural, 50 m×8 shuttle-running and sit-ups was (125.22 ± 15.57) s and 24.96 ± 8.97 for those with early menarche, while it was (120.92 ± 13.06) s and 22.96 ± 9.83 for those without menarche. There were significant differences between two groups on both variables(t values were 3.89 and 2.77 with both P values < 0.01). In addition, 50 m×8 shuttle-running in girls (10.0-10.9 years old) with early menarche was (128.52 ± 15.74) s and it was (123.89 ± 13.50) s in girls without menarche. The difference was significant (t = 2.14, P < 0.05). The multilevel analysis showed that 50 m running, standing broad jump and sit-ups in girls with early menarche was 0.12 s, 3.14 cm and 1.11 higher than girls without menarche (Waldχ(2) values were 4.00, 6.22 and 4.07, respectively with all P values < 0.05). But 50 m×8 shuttle-running in girls with early menarche was 1.95 s less than girls without menarche (Waldχ(2) = 3.96, P < 0.05). CONCLUSION: Early menarche may be associated with higher speed fitness, leg power and muscle power and lower physical stamina.

[Influence of diet behaviors on height among children and adolescents in China: a multiple level analysis].

OBJECTIVE: To categorize growth and development stages among children and adolescents based on height, and to explore the influences of diet behaviors on height during different growth and development stages. METHODS: Children and adolescents (7 to 18 years) with normal weights were selected using "Reference Norm for Screening Overweight and Obesity in Chinese Child and Adolescent" set up by WGOC in 2003 and "Reference Norm for Screening Underweight in Chinese Child and Adolescent" from the "2010 National Physical Fitness and Health Surveillance" data, and the variables of height and diet behaviors sorted. The growth and development stages were categorized using the hierachical cluster analysis, and the multilevel model was used to analyze influences of diet behaviors on height at different growth and development stages. RESULTS: Basis on height, there were 4 growth and development stages among the children and adolescents. In the boys, growth and development stages included Pre-GSS (growth spurt stage, GSS) including 7 to 10 years, GSS (11 to 12 years), Post-GSS (13 to 14 years), and growth stability stage (15 to 18 years); in the girls, the stages included the fast velocity GS (growth stage, GS) including 7 to 10 years, GS (11 to 12 years), Post-GS (13 to 15 years), and growth stability stage (16 to 18 years). The results of the multilevel model showed that the students' height in the urban areas were higher than in the rural areas (P<0.01), and the trend of difference between the urban and rural areas with the different growth stages was a parabola shape, the highest differences were 3.36 cm and 3.23 cm in the GSS and the fast velocity GS, respectively. There were significant influences of breakfast on height during the Pre-GSS and the fast velocity GS (P<0.01), and increased 0.40 cm and 0.57 cm, respectively. Excluding the stablility growth stage in the girls, drinking milk increased significantly height during the different growth stages (P<0.01), and the increases were gradual downtrend with the growth stages, the highest increase was 0.91 cm and 0.94 cm in Pre-GSS and the fast velocity GS, respectively. Eating eggs increased significantly height during all the growth stages (P<0.01), and the increases were the gradual uptrend with different growth stages. There were interaction effects among breakfast, drinking milk and eating eggs during the different growth stages, which was the gradual downtrend. CONCLUSION: Breakfast and drinking milk are conducive to growth during early adolescence, and the effect of eating eggs on growth is gradual uptrend with different growth stages.

[Comparative study of sexual behaviors of high school students between urban and rural China].

OBJECTIVE: To analyze the situation of sexual behavior in urban and rural Chinese high school students, and to make suggestions for providing appropriate sexual education in the future. METHODS: An anonymous questionnaire survey was conducted in 224 770 high school students selected by using multi-stage stratified cluster sampling method in 28 provincial units of China. RESULTS: Overall, 5.9% high school students reported that they had had sexual intercourses, and the prevalence rate of having had sexual intercourses was higher in the urban students (6.2%) than in the rural (5.2%) students (χ(2)=83.290, P<0.01), and higher in the boys (8.8%) than in the girls (3.3%, χ(2)=2 944.456, P<0.01). Of all the subjects, 44.6% reported that they had forced sex; the prevalence rates were 43.5% and 47.5% in the urban and rural students (χ(2)=16.237, P<0.01), respectively, and lower in the boys (39.7%) than in the girls (55.8%, χ(2)=285.089, P<0.01). Boys, higher grades, vocational schools, living without their parents and in areas of West China were found to be the risk factors to sexual intercourses in the urban and rural students. The pattern of forced sexual intercourses was slightly different between the urban and rural students, however, girls, ordinary schools, living without their parents and in areas of West China were the risk factors. CONCLUSION: Sexual education should be taken as soon as possible by using scientific as well as systematic methods in the occupational school students, and students living without their parents and in areas of West China.

[The trend analysis of overweight and obesity in Chinese students during 1985 - 2010].

OBJECTIVE: To analyze the trend of overweight and obesity in students in China during 1985 - 2010. METHODS: The data were from Chinese National Survey on Students Constitution and Health in 1985, 1995, 2000, 2005 and 2010, and the sample sizes were 204 977, 216 786, 234 421, 215 319, respectively. BMI was calculated with height and weight. The prevalence of overweight and obesity as well as the rates of increase were described based on the BMI percentile criteria of Working Group on Obesity in China (WGOC). RESULTS: In 2010, the prevalence of overweight and obesity in four groups students (urban boys, urban girls, rural boys, and rural girls aged 7 - 18 years) were 23.23% (12 503/53 830), 13.76% (7 414/53 857), 12.72% (6 839/53 744), 8.56% (4 612/53 888), respectively, which were higher in boys and urban, and reached the peak 17.14% (18 463/107 741) in students aged 7 - 12 years. The prevalences of obesity were 0.44% (8/1800) - 21.67% (390/1800) among children aged 7 - 18 years in different provinces. The prevalence of overweight and obesity during 1985 - 1995, 1995 - 2000, 2000 - 2005 and 2005 - 2010 increased 0.10%, 0.30%, 0.23%, 0.23%, respectively, and the increase rate was higher in urban than in rural during 1985 - 2005. During 1985 - 1995, the increase rate of obesity in four groups students were 0.20%, 0.13%, 0.05% and 0.03%, respectively. During 2005 - 2010, the increase rates of obesity in four groups of students were 0.30%, 0.10%, 0.34%, 0.17%, respectively, and the increase rate was higher in rural than in urban. CONCLUSION: The prevalence of obesity among 7 - 18 years-old children increased rapidly during the 1985-2000, and the increase rate of obesity in rural exceeded that in urban during 2005 - 2010.

[Behavioral risk factors for overweight and obesity among Chinese primary and middle school students in 2010].

OBJECTIVE: To explore the associations between behavioral risk factors and overweight and obesity among Chinese primary and middle school students in 2010. METHODS: A total of 149 912 primary and middle school students aged 9 - 18 were selected from "2010 National Physical Fitness and Health Surveillance" while underweight students excluded. Questionnaires and height, weight and other physical index were performed. Logistic regression was used to analyze the association between overweight, obesity and sleep time, diet, physical exercise intention and behavior as well as sedentary behavior. RESULTS: Of students surveyed, the proportion of short sleep time was higher in obese students than in normal weight students, the prevalence of short sleep time was 93.60% (118 394/126 491), 94.39% (15 053/15 947) and 95.09% (6782/7132) in normal weight, overweight and obese students, respectively (P < 0.05); the proportion of egg intake with no more than 3 times per week was lower in obese students than in normal weight students (56.49% (4025/7125) vs 65.25% (82 518/126 464)) (P < 0.05); the proportion of never drinking milk was lower in obese students than in normal weight students (7.08% (505/7134) vs 7.55% (9 545/126 503)) (P < 0.05); and when compared with those of normal (29.53%, 37 354/126 482), more overweight students reported that they had spent 2 or more hours on homework (30.17%, 4 809/15 941) (P < 0.05). The proportions of physical activity intentions were significantly lower in obesity group of male students than those of normal male group, and the proportion of liking physical education, being willing to participate in the extracurricular sports activities, and being willing to participate long running exercise was 67.7% (4828/7134), 71.2% (5083/7135) and 35.9% (2560/7135) in obese students compared with 68.6% (86 776/126 511), 72.6% (91 814/126 509) and 47.4% (59 914/126 512) in normal weigh students, respectively. In the 13 - 15 age group, the proportion of having been physically active for a total of at least 60 minutes per day was lower in obese group (19.87%, 376/1893) than in normal group (20.66%, 8 253/39 941) (P < 0.01). Logistic regression analysis showed that the students with short sleep time were more likely to get obesity than those without short sleep time (adjusted odds ratio (AOR): 1.11, 95%CI: 1.00 - 1.25). Egg intake with no more than 3 times per week was negatively associated with the probabilities of being at risk for obesity (AOR: 0.88, 95%CI: 0.83 - 0.92), while, never drinking milk was independently related to obesity (AOR: 1.14, 95%CI: 1.03 - 1.25). Disliking physical education (AOR: 1.23, 95%CI: 1.16 - 1.30), unwilling to participate long running exercise (AOR: 2.16, 95%CI: 2.05 - 2.28) and spending 2 or more hours on homework (AOR: 1.09, 95%CI: 1.02 - 1.15) were independently related to obesity. The patterns of influence factors in different groups were not alike. CONCLUSION: Overweight and obesity prevalence was higher in China's primary and middle school students in 2010, and the bad dietary behavior, static life style were highly interconnected.

[Relationship between obesity, overweight and physical function in students of Han nationality aged 7 - 18 years in 2010].

OBJECTIVE: To study the effects of overweight and obesity on physical function (including systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse, weight vital capacity index) in children and adolescents. METHODS: The data of 2010 Chinese National Survey on Students Constitution and Health was analyzed. The samples of overweight and normal-weight group were randomly selected from the data by matching gender, urban or rural for getting the same number sample size as obese group (10 601 each group). The students aged 7 - 18 years were classified into 3 groups by BMI percentiles (P5, P15, P25, P50, P75, P85 and P95), to analyze the change of physical function along with BMI percentile. RESULTS: Compared to the normal-weigh group, SBP of the obese boys of all age groups increased by 8.0 - 12.0 mm Hg, DBP increased by 4.7 - 5.9 mm Hg, while SBP of the obese girls increased by 7.5 - 11.6 mm Hg, DBP increased by 4.7 - 6.1 mm Hg, with statistical significance (P < 0.05). In 13 - 15-year group, pulse of obese boys was 0.8 times/min higher than that of normal-weight. In 16 - 18-year group, pulse of obese boys was 1.1 times/min higher than that of overweight or normal-weight, while pulse of obese girls were 1.5 and 1.7 times/min higher than that of overweight and normal-weight, respectively (P < 0.05). Pulses in boys aged 7 - 9 years when BMI were P5, P50, P(95) were 87.63, 87.00, 87.83 times/min, and pulses in boys aged 10 - 12 were 85.66, 85.30, 85.43 times/min, respectively. Pulses in boys aged 13 - 15 years when BMI were P5, P50, P95 were 82.60, 81.39, 82.34 times/min, and pulses in boys aged 16 - 18 years were 80.15, 79.00, 79.98 times/min. In both boys and girls of all age groups, weight vital capacity index had the trend of obese < overweight < normal-weight (P < 0.05). Compared to the normal-weight group, weight vital capacity index of overweight boys decreased by 6.4 - 8.4 ml/kg, that of obese boys decreased by 11.9 - 14.8 ml/kg, while that of overweight girls decreased by 5.3 - 7.7 ml/kg, that of obese girls decreased 11.0 - 11.5 ml/kg. CONCLUSION: Compared to the normal-weight, overweight and obese children and adolescents had elevated blood pressure, increased pulse, decreased weight vital capacity index.

[Current situation of semenarche in boys aged 11-18 of 18 Chinese ethnic minority].

OBJECTIVE: To analyze the current situation of semenarche in boys aged 11 - 18 of 18 Chinese ethnic minority, and compare the average age of semenarche with Chinese Han boys from the same province or autonomous region. METHODS: The average age of semenarche in various ethnic minority groups of Chinese boys who participated in 2005 National Physical Fitness and Health Surveillance were calculated. The sample size of ethnic minority boys was 16 267, and the ethnic minorities were Mongolian, Hui, Tibetan, Korean, Zhuang, Miao, Buyi, Dong, Shui, Tujia, Bai, Hani, Dai, Lisu, Wa, Naxi, Li and Tu. The local Han boys semenarche were also surveyed in 2005 National Physical Fitness and Health Surveillance. Probability unit regression, chi2 test, U test and dynamic clustering were used to calculate and analyze the average age of semenarche. RESULTS: In the 13 years old group,the percentage of semenarche in Dong was lowest (5.00%, 5/100), while that in Li was the highest (68.35%, 54/79) (P<0.01). In the 14 and 15 years old group,the percentages of semenarche in Shui were the lowest (17.02%, 16/94; 22.83%, 21/92, respectively) (all P values <0.01), while the percentages in Zhuang were the highest (94.33%, 183/194; 98.45%, 191/194, respectively).When reached 18 years old, 97.85% (2137/2184) ethnic minority boys experienced semenarche. The top 3 ethnic minority groups in average age of semenarche were Korean (12.37 years old), Zhuang (13.34 years old) and Naxi (13.36 years old); and the last 3 ethnic minority groups were Shui (16.19 years old), Bai (15.27 years old) and Tu (15.19 years old). The average age of semenarche in Zhuang was 1.34 years earlier than that of Han boys from Guangxi Zhuang autonomous region; the average age in Korean was 1.28 years earlier than that of Han boys from Jilin province; and the average ages in Naxi and Dai were 0. 89 years and 0. 17 years earlier than that of Han boys from Yunnan province, respectively (all P values < 0. 01). The cluster analysis indicated that the 18 ethnic minority groups could be classified into two groups: Zhuang, Naxi, Li and Korean were classified into earlier age group of semenarche, and the other 14 ethnic minority groups were belonged to later age group of semenarche. CONCLUSION: There was a large variation among different ethnic minority groups in terms of average age of semenarche. The semenarche was earlier in Zhuang, Korean, Naxi, and Dai, compared with local Han boys.

[Changes on secular growth among minority girls in China from 1985 to 2005].

OBJECTIVE: To analyze the trend of secular growth among the minority girls in China from 1985 to 2005 in order to develop national and local intervention strategies and measures to improve their physical fitness and health. METHODS: A total of 19 Chinese minority girls, including Mongolian, Hui, Zhuang, Korean, Tibetan, Miao, Buyi, Dong, Yao, Bai, Tujia, Hani, Dai, Lisu, Wa, Nakhi, Tu, Qiang and Salar were sampled from the 1985 and 2005 Chinese national surveys to study the students' physical fitness and health. Probit analyses were used to calculate age at menarche (AAM), and the heights and weights of 17-years-old girls in various minority groups. RESULTS: From 1985 to 2005, the increments of adult heights and weights increased significantly in many minority groups. The average height of girls aged 17 years old in each minority group had an increase of 150 cm in 2005. Ethnic groups with height growth rates of more than 1 cm per decade in girls aged 17 years old were Korean (1.47 cm/decade), Tujia (1.38 cm/decade), Qiang (1.32 cm/decade), Bai (1.25 cm/decade), Hui (1.13 cm/decade) and Buyi (1.07 cm/decade). And the minority ethics with weight growth rates of more than 1 kg per decade in girls aged 17 years old were Mongolian (1.79 kg/decade), Korean (1.69 kg/decade), Tibetan (1.66 kg/decade), Nakhi (1.39 kg/decade), Qiang (1.28 kg/decade) and Hui (1.10 kg/decade). The overall AAM showed a downward rate in all the 19 minority groups, but with different degrees. Tujia, Yao and Nakhi showed the largest reductions, with AAMs as 2.15, 1.76 and 1.38 years earlier in 2005 than in 1985, respectively. CONCLUSION: Our data suggested that the downward secular trend in AAMs and the increments of adult heights might reflect the secular growth change in the major minority groups during the past 20 years, but there was an obvious disequilibrium of puberty development and increments of heights in adults between the minority groups.

The epidemiology of alcohol consumption and misuse among Chinese college students.

AIMS: To understand alcohol-related risk behaviours among Chinese college students. METHODS: As part of the first China National Youth Risk Behaviour Survey, undertaken in 2009, 52,150 students at 119 colleges were randomly sampled. Information was obtained from self-administered questionnaires. RESULTS: Prevalences were: lifetime drinkers 80.8%, current drinkers 49.3% (drank alcohol in past 30 days) and binge drinkers 23.5% ('binge drinkers' reporting at least five alcoholic drinks on a single occasion at least six times during the past 30 days). Multinomial logistic analysis revealed the contribution of sociodemographic factors to three high-risk drinking behaviours: odds ratio (95% confidence interval) = 3.64 (2.69-4.60) with frequent drinking; 3.27 (1.82-4.72) with binge drinking; and 5.48 (3.20-7.77) with heavy binge drinking. These three rates were greater among males than females, in the Western more than the Eastern region, among students living off-campus and among those whose mothers had higher education. Heavy drinking was linked to lower academic self-rating. CONCLUSION: There is a trend towards risky drinking among Chinese college students. Measures such as a minimum drinking age, advertisement restrictions, taxation, drunk-driving penalties and campaigns to heighten public awareness of alcohol-related health risks should be instituted in order to improve the situation on college campuses where alcohol abuse is particularly prevalent.

[Study of geographic distribution and 10 years' change of spermarche in Chinese boys of Han-group aged 11 to 18].

OBJECTIVE: To analyze the geographic distribution and 10 years' change of spermarche in Chinese boys of Hangroup aged 11 - 18. METHODS: Calculate the average age of spermarche of Chinese boys who participated in National Physical Fitness and Health Surveillance in 2005 and 1995. The sample size of boys was 69 320 in 2005, 68 992 in 1995 National Physical Fitness and Health Surveillance, respectively. The geographic distribution of Chinese boys were categorized into 6 areas as north, northeast, east, south central, southwest and northwest by administrative divisions. RESULTS: The average ages at spermarche were 13.98 and 14.22 years old for urban and rural boys in 2005, respectively. The average ages at spermarche were 13.57 and 13.72 years old for urban and rural boys who living in southwest of China. And the average ages at spermarche were 14.18 and 14.39 years old for urban boys who lived in northwest of China, and rural boys who lived in south central of China, respectively. The average age of spermarche of the top 5 provinces were Chongqing (13.28), Guizhou (13.47), Hainan (13.47), Sichuan (13.56) and Tianjin (13.61); and the last 5 provinces were Hubei (15.30), Qinghai (15.13), Liaoning (14.75), Guangxi (14.68) and Shanghai (14.55). The average ages of spermarche were 14.43 and 14.77 years old for urban and rural boys in 1995, respectively, and thus the ages of spermarche in 2005 were 0.45 and 0.55 years earlier than that of urban and rural boys in 1995. CONCLUSION: There was a large variation among different geographic areas. The onset of spermarche was generally earlier in urban than in rural boys, the earliest in southwest of China, and the latest in northwest and south central of China. Significant decline trend of age at spermarche could be found in Chinese boys, especially in rural areas.

[Geographic distribution and secular trend of menarche in 9-18 year-old Chinese Han girls].

OBJECTIVE: To analyze the characteristics and secular trend of age at menarche (age at menarche, AAM) in Chinese girls aged 9-18. METHODS: Probit analyses were used to calculate AAMs in various populations of Chinese girls who participated in National Physical Fitness and Health Surveillance in 2005 or 1995. The samples of girls were 92 767 in 2005 and 85 433 in 1995 National Physical Fitness and Health Surveillance, respectively. RESULTS: AAM was 12.76 years in Chinese girls aged 9-18 in China. AAMs were 12.60 and 12.92 years for urban and rural girls, respectively. There was a large variation among different geographic areas, and AAM was earlier in girls living in east of China and later in girls living in northwest of China. AAMs of the top 5 municipalities/provinces were Beijing (12.27 years), Shanghai (12.32 years), Sichuan (12.48 years), Fujian (12.50 years) and Tianjin (12.51 years); and the last 5 provinces/autonomous regions were Qinghai (14.09 years), Hubei (13.33 years), Heilongjiang (13.10 years), Ningxia (13.08 years) and Hunan (12.87 years). AAMs were 0.22 and 0.34 years earlier than those of urban and rural girls in 1995. CONCLUSION: The onset of menarche was generally earlier in urban than in rural girls, and the latest in northwest of China. Significant decline trend of age at menarche could be found in Chinese girls, especially in rural areas. The differences of AAMs among urban and rural areas and in various provinces were with a tendency to shrink in 2005 compared with 1995.

[Study on the characteristics of sexual intercourse debut and its influencing factors among college students in 18 provinces in China].

OBJECTIVE: To describe the characteristics of sexual debut among college students in China to provide appropriate sex education in that population. METHODS: An anonymous questionnaire survey was conducted among 33 653 college students selected by multi-stage stratified cluster sampling method in 18 provinces and cities of China. RESULTS: The percentage of students who had initiated sexual intercourse before age 14 was 1.9%. Overall, male students (2.8%) were significantly more likely to have initiated sexual intercourse before age 14, than female students (1.1%). The percentage of students who had initiated sexual intercourse from age 15 to 18 was 6.4% in males versus 2.1% in females. while the rates of students who had initiated sexual intercourse after age 19 were 6.9% in males and 2.6% in females. The first sexual intercourse was significantly associated with parental educational attainment, geographic location and family structure. Students whose parents were relatively well educated, living in the western areas of the country China, or with nucleus/extensive families were more likely to have early sex in their puberties. CONCLUSION: Sexual education should be strengthened especially in the western areas, and targeted on the students whose parents with relatively higher educational background or who were from extensive families.

[Secular growth trends in height and weight of Chinese children aged 7 to 18 year-old from 1985 to 2005].

OBJECTIVE: To analyze the secular changes in height and weight of Chinese school children in recent 20 years, in order to take effective preventive strategies and measures to improve their physical fitness and health. METHODS: Students aged 7-18 year-old participated in the 1985, 1995 and 2005 National Survey on Students Constitution and Health were used as subjects. The LMS method was applied to draw the 5th, 50th and 95th smoothed percentile curves of height and weight, and comparison was analyzed between different years. RESULTS: From 1985 to 1995, the 50th percentile of average height increased by 3.1, 3.5, 2.2 and 2.8 cm, and the 50th percentile of average weight increased by 3.2, 1.9, 2.0 and 1.3 kg, for urban boys, rural boys, urban girls, rural girls respectively. The average increments of height were 2.0, 2.3, 1.3 and 1.7 cm, and the average increments of weight were 3.1, 1.9, 1.7 and 1.2 kg during 1995 to 2005. The secular growth trends in the recent 20 years were: (1) height and weight had increased in each age group of students. (2) the 95th percentile curves of height and weight were higher than 50th and 5th percentile curves. (3) the average increments per decade in rural students were higher than those in urban students. (4) the average increments of height per decade for aged 18 year-old were lower than those in other age groups. (5) the average increments of height during 1985-1995 were higher than that during 1995-2005, but increments of adult height during 1985-1995 were lower than that during 1995-2005. CONCLUSION: A significant secular increase in height and weight was found in school children aged 7-18 year-old in China, and the secular increase was more obvious among well-grown school children.

[Prevalence rates of overweight and obesity in Chinese minority students in 2005].

OBJECTIVE: To analyze the prevalence rates of overweight and obesity in Chinese minority students in 2005. METHODS: We analyzed data of 24 minority groups aged 7 - 18 years from Chinese national survey on students' physical fitness and health in 2005. Criterion made by the workgroup of obesity in China (WGOC) was used. RESULTS: The prevalence rates of overweight in 24 minority groups aged 7 - 18 years were 3.71% for boys and 4.72% for girls, while the prevalence rates of obesity were 1.60% for boys and 1.25% for girls. The total prevalence rates of overweight and obesity were 5.32% for boys and 5.96% for girls. The prevalence rates of overweight and obesity were higher in Korean, Mongolian and Kazak but lower in Zhuang and Shui students the Korean students the highest. CONCLUSION: In general, both the prevalence rates of overweight and obesity in Chinese minority students were comparatively low. However, in some minority groups the prevalence had already become higher, which demands early prevention.

[Study on the trend of minority students' health status from 1995 to 2005 in China].

OBJECTIVE: To reveal the trend of minority students' health from 1995 to 2005 in China. METHODS: We selected 15 minority groups wtih data pertaining to students' nutritional status, poor vision and decayed tooth in 1995, 2000 and 2005. The minority groups were Mongolian, Hui, Uygur, Zhuang, Korean, Tibetan, Yao, Li, Qiang, Bouyei, Dong, Hmong, Tu, Salar and Kirgiz. RESULTS: The prevalences of underweight and malnutrition in 2005 in Mongolian, Hui, Uygur, Zhuang and Korean students aged 7 - 22 years were lower than that of 1995 and 2000, indicating the nutrition status was improved. The prevalence of malnutrition in city girls was the highest. The mild malnutrition rates in 2005 decreased to 2.69%, 4.67%, 3.68%, 9.62% and 2.65% but the prevalence of overweight and obesity increased. For city boys, the rates were 5.50%, 8.12%, 2.69%, 3.69% and 13.50%. The prevalence of decayed tooth changed but with no significant differences. The prevalence rates of poor vision and myopia kept increasing. The minority students' myopia rates in 2005 were 29.5%, 39.1%, 10.1%, 42.6%, 41.1%, for boys and 45.4%, 50.0%, 15.4%, 49.7%, 46.7% for girls. CONCLUSION: In order to improve the health of students in minority regions, we need to promote health education at schools.