| PrefaceBody composition is the summation of body components, which can be divided into body fat and lean body mass. If percentage body fat is beyond some certain range, obesity is coming.When children entering puberty, body fat are changing greatly. The relationship between body composition and endocrine hormone has been confirmed. The simple obesity and adolescent endocrine have close relationship. Sex hormone has special effect on growth spurt, protein synthesis, lipid metabolism and bone developing.Some researchers determined testosterone and estradiol levels in saliva are correlated significantly positively with those in blood. But their subjects are almost adults, or study the relationship between testosterone levels in saliva and sex developing of boys, and there are few reports about salivary androgen levels of girls in early puberty or the relationship between salivary estrogen levels and body composition of boys. The study is a three - year semi - longitudinal study between body composition and sex hormone levels in boys and girls aged 8 and 10 to require the data about the growth and development of children inearly puberty and their sex hormone levels and to study the relationship between body composition and salivary testosterone and estradiol levels.SubjectsCluster sampling was used to get boys (359 in 8 years, 371 in 10 years) and girls (327 in 8 years, 370 in 10 years). After asking history and regular health examination, height, weight, skinfold thickness and sexual organ development level were measured. We determined their secondary sexual character according on Tanners method.All boys were divided into three groups ( obese, median, lean) according on the percent body fat that was calculated based on the skin fold. Every individual of groups were matched by age, height and secondary sexual character into pairs ( obese; median; lean ratio is 1: 1: 1). In the matched pairs, height difference was no more than 1 cm and secondary sexual character was in the same period. Finally 129 boys (63 in 8 years, 66 in 10 years) and 147 girls (72 in 8 years, 75 in 10 years) were filtered as objects and observed two years.Materials and Methods1. The measurement of height and weight was based on the " the research of constitution and health in Chinese students".2. The measurement of skinfold thickness; 2. 1 Instrument: Harpenden forceps.2.2 Site; Left biceps brachii, triceps brachii, subscapular angle and iliopelvic skinfold.3. Secondary sexual character determination was based on the method of " Human Growth II ".4. The assay of salivary sex hormone: radioimmunoassay (RIA) was used to determine testosterone, chemiluminescent enzyme linked immunoassay was used to determine estradiol.5. Error control: all the indices were determined by professionals, samples of the same year were detected together. CV was 5.4% of testosterone test kit in one batch, 9. 5% in batches; 3.7% of estradiol test kit in one batch, 7.0% in batches.6. Statistic and analysis:6.1 Percent body fat ( % BF) :boys: %BF=6.931+0.428Xgirls: %BF =7. 896+0.458X X is the sum of skinfold thickness of triceps branchii and sub-scapular angle.6. 2 Total body fat ( TBF) : TBF = W x % BF ( W is weight) 6. 3 Lean body mass ( LBM) : LBM = W - TBF Statistic and analysis were done by SPSS 10.0 software.ResultsHeight and weight of all boys and girls increased with age. On the whole, BF and LBM raised with age. % BF of boys in obese group increased from 8 to 10, decreased from 11 years; % BF in median group decreased from 12 years but in lean group increased all the time. % BF of girls in obese group decreased from 10 years, while in median and lean groups increased at all times.Salivary testosterone and estradiol levels of all boys girls increased with age. Testosterone levels in obese group were lower thanmedian and lean group, but it was only significant at 10. Estradiol levels in obese group were higher than lean group except 9. About girls: Salivary testo...
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