| Objective:Bone mass in adolescents was affected by many factors. Most previous studies examined the effects of different environmental factors on bone mass in children and adolescents by means of cross-sectional studies or intervention trials. However, few studies compared bone mass in adolescents at the same age in different years. Our study selected subjects aged 12-14 from suburb of Beijing in 2002 and 2009 respectively. We compared their bone mass and analysed the reasons of differences betweeen the two groups to provide basic datas for promoting bone health in children and adolescents in china through this research.Methods:A total of 619(313 in 2002 and 306 in 2009)healthy adolescents aged 12-14 were recruited randomly from the suburb of Beijing. Sbujects' height and weight were mearsured and their general information, family background, dietary intake and pubertal development were collected by questionnaires. Bone mineral mass, bone area of total body and lumbar, body component were measured using dual-energy X-ray absorptiometry (DEXA). The differences between two groups were compared using chisquare test, t-test, rank test and Ridit analysis. The multiple linear regression was used to select the fators that influencing bone mass and evaluate the associations between fators and bone mass.Results:1.(1)General information:A total of 619 adolescents took part in our study, whose mean(±SD) age 13.3±0.7 y. Adolescents in 2002 (13.6±0.7y)was older than those in 2009(13.1±0.7y). The proportion of minority(10.5%) in 2002 was lower than which in 2009(18.1%), The proportion of boarder(50.3%) in 2002 was higher than which in 2009(19%).but there was no signficant difference in the proportion of sex between the two groups (P>0.05).(2) Family background:There was no significant difference in the mean age of subjects'parents between in the two groups(P>0.05). But the educational level's distribution in subjects'parents was different(P<0.05).(3) Dietary intake:Dietary energy, protein, sodium, calcium, magnesium, iron, zinc, cooper, phosphor selenium intake of subjects in 2002 and 2009were 1689.2kcal and 1720.2kcal,55.7g and 60.5g,681.9mg and 791.0mg,346.2mg and 272.2mg,262.6mg and 233.6mg,19.1mg and 15.0mg, 10.0μg and 8.3μg, 1.4mg and 1.1 mg,915.3mg and 867.7mg,36.3mg and 35.1mg. In addition to dietary iron intake of students in 2002, other nutrients intake did not meet 14-year-old'RNI/AI of Chinese DRIs. Energy contribution from fat was 21.1%-22.6%, which was lower than 25%～30%level.Dietary fat(44.7g), calcium (366.3mg), magnesium(278.6mg), iron(22.2mg), zinc(11.2μg), cooper(1.5mg) and phosphor(1040.7mg) intake of boys in 2002 were higher than those of boys in 2009(43.2g,264.3mg,239.9mg,15.0mg,8.3μg, 1.0mg and 885.8mg, respectively), but whose dietary fibre(9.0g) intake was lower than the latter'(11.9g). Dietary calcium(323.5mg), iron(17.4mg), zinc(8.7μg), cooper (1.3mg) intake of girls in 2002 were higher than those of girls in 2009(279.3mg, 15.4mg,8.0μg and 1.1mg, respectively), but whose dietary protein(49.5g) and fibre intake(7.8g) were lower than those of girls in 2009(56.4g and 11.6g).(4) The proportion of boys who reached first spermatorrhea were not different between two groups (P>0.05) but the proportion of girls reached menarche in 2002(77.8%) were higher than that in 2009(65.2%). Boys'pubertal staging were primary in Tanner stage ofⅡ～Ⅳ, while that of girls'were in Tanner stage ofⅡ～Ⅲ(P<0.05). The pubertal staging of boys and girls in 2002 was higher than that of boys and girls in 2009(P<0.05).2. The trunk BMD of boys aged 13 y in 2002(0.884±0.095g/cm2) were higher than that of boys at the same age in 2009(0.838±0.079g/cm2). The height, weight, body composition, and bone mass at other sites of boys aged 12-14 y in 2002 were not significantly different from those of their counterparts in 2009(P>0.05). The upper limbs BMC and BMD of girls aged 12 y(198.0±36.2g, 0.439±0.053 g/cm2) and the upper limbs BMC of girls aged 13y(214.7±32.1g) in 2002 were lower than those of girls at the same age in 2009(217.5±41.8g, 0.471±0.066g/cm2,230.1±46.1g, respectively). The trunk BMD (0.910±0.092 g/cm2), lower limbs BMC(700.3±113.6g) of girls aged 13y were higher than their counterparts in 2009(0.870±0.094g/cm2 and 654.3±123.5g). The total body and lower limbs BMC,BMD and trunk BMD of girls aged 14 in 2002 (2128.1±258.6g and 0.840±0.065g/cm2,770.1±96.0g and 0.874±0.076g/cm2,0.964±0.078g/cm2) were higher than their counterparts in 2009(1984.0±182.9g and 0.795±0.050 g/cm2,670.3±60.3g and 0.837±0.042 g/cm2,0.884±0.060 g/cm2), respectively. The lean body mass of girls aged 12y(28.9±5.2kg) in 2002 were lower than their counterparts in 2009(32.2±5.0kg), and the height, weight of girls aged 14 in 2002(159.4±4.7cm and 50.9±6.9kg) were higher than their counterparts in 2009(156.6±4.2cm and 47.1±4.9kg). The other indices were not different between different years(P>0.05).3. Multiple liner regression analysis:R2 of the multiple linear regression equation for total body BMC of boys were 0.872.The main determinant fator of total-BMC of boys was the weight, following by height, age, pubertal staging, underweight, and dietary energy intake. R2 of the multiple linear regression equation for total body BMC of girls were 0.854. The main determinant fator of total-BMC of girls was lean body mass, following by height, PBF, malnutrition, pubertal staging underweight and age. R2 of the multiple linear regression equation for total body BMD of boys were 0.729.The main determinant fator of total-BMD of boys was weight, following by height, obesity, dietary energy intake age and dietary calcium intake. R2 of the multiple linear regression equation for total body BMD of girls were 0.737.The main determinant fator of total-BMD of girls lean body mass, following by PBF, year, pubertal staging, boarding, and age.R2 of the multiple linear regression equation for lumbar BMC of boys were 0.701.The main determinant fator of lumbar BMC of boys was lean body mass, following by pubertal staging, height and year. R2 of the multiple linear regression equation for lumbar BMC of girls were 0.726.The main determinant fator of lumbar BMC of girls was also lean body mass, following by height, pubertal staging, malnutrition, menarche and year. The main determinant fator of lumbar BMD of boys was lean body mass, following by pubertal staging. R2 of the multiple linear regression equation for lumbar BMD of boys were 0.614. The main determinant fator of lumbar BMD of boys was lean body mass, following by pubertal staging, age, year,boarding and underweight. R2 of the multiple linear regression equation for lumbar BMD of girls were 0.611.The main determinant fator of lumbar BMD of girls was also the lean body mass, following by pubertal staging, menarche,year, boarding and PBF.R2 of the multiple linear regression equation for trunk BMC of boys were 0.772.The main determinant fator of trunk BMC of boys was weight, following by obesity, overweight, pubertal staging, age and dietary phosphor intake. R2 of the multiple linear regression equation for trunk BMC of girls were 0.777.The main determinant fator of trunk BMC of girls was lean body mass, following by height, PBF, malnutrition, pubertal staging, underweight and age. R2 of the multiple linear regression equation for trunk BMD of boys were 0.582.The greatest determinant fator of trunk BMD of boys was weight, following by height, year, leanbody mass, pubertal staging, overweight and dietary protein intake. R2 of the multiple linear regression equation for trunk BMD of girls were 0.631.The main determinant fator of trunk BMD of girls was lean body mass, following by year, pubertal staging and boarding.R2 of the multiple linear regression equation for upper limbs BMC of boys were 0.805.The main determinant fator of upper limbs BMC of boys was lean body mass, following by PBF, height and age. R2 of the multiple linear regression equation for upper limbs BMC of girls were 0.738. The main determinant fator of upper limbs BMC of girls was also lean body mass, following by height, weight, pubertal staging, PBF, malnutrition and dietary protein intake. R2 of the multiple linear regression equation for upper limbs BMD of boys were 0.790.The main determinant fator of upper limbs BMD of boys was lean body mass, following by PBF, height and age. R2 of the multiple linear regression equation for upper limbs BMD of girls were 0.734.The main determinant fator of upper limbs BMD of girls was also lean body mass, following by PBF, pubertal staging, height, boarding, age and dietary calcium intake. R2 of the multiple linear regression equation for lower limbs BMC of boys were 0.895.The main determinant fator of lower limbs BMC of boys was weight, following by lean body mass, height, year, obesity, dietary calcium intake,and overweight. R2 of the multiple linear regression equation for lower limbs BMC of girls were 0.872.The main determinant fator of lower limbs BMC of girls was height, following by lean body mass, year, PBF, malnutrition and underweight. R2 of the multiple linear regression equation for lower limbs BMD of boys were 0.718.The main determinant fator of lower limbs BMD of boys was weight, following by dietery phosphorus and calcium intake, overweight and boarding. R2 of the multiple linear regression equation for lower limbs BMD of girls were 0.713.The main determinant fator of lower limbs BMD of girls was lean body mass, following by height and pubertal staging.Conclusions:The fators influencing bone mass of the same and different skeletal region between pubertal boys and girls aged 12-14 were different. Effect of the same fator on different gender and bone mass of different skeletal region is different.Differences of bone mass of boys in 2002 and 2009 associated with the differences of age. The differences of total bone mass of girls in 2002 and 2009 associated with the differences of age, height and pubertal staging, differences of trunk bone mass associated with the differences of pubertal staging, difference of upper limbs bone mass associated with the differences of age, LBM, dietary calcium and protein intake, difference of lower limbs bone mass associated with the differences of heights and pubertal staging. |
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