| Objectives To observe the effect of milk powder fortified with calcium onconstitution growth, body compositon and bone development of adolescents insuburban district in Beijing, as well as to provide scientific basis for improving thenutritional status of them.Methods The design was a randomized controlled intervention trial. Three smalltowns were selected from a Huairou District, Beijing, and one secondary school wasselected randomly from each small town. All286healthy adolescents were recruitedfrom grade one students of all three schools. After bone mineral contents wasmeasured at baseline, students were randomly devided into one control group andthree intervention groups by baseline bone mineral contents basing on no significantdifferences in it. The control group subjects maintained usual daily diet withoutintervention. All the intervention group subjects were randomly divided into threegroups by individual: a group (supplied with40g milk powder fotified with300mgcalcium and10μg vitamin D), b group (supplied with40g milk powder fotified with600mg calcium and10μg vitamin D), c group (supplied with40g milk powderfotified with900mg calcium and10μg vitamin D). Parents were required to preparemilk powder for students at morning and evening, and students had to drink themunder parents’ intendance. The intervention course was one and half year.Questionaire surveies were used to collect subjects’ general information, familyenvironments, dietary intake, and physical activity. Development and growth was alsoexamined. Double Energy X-ray Absorptiometry (DEXA) was used to measue Bone Mineral Content (BMC), Bone Mineral Density (BMD), Bone Area (BA) and totalbody composition at baseline, metaphase (one year after baseline) and the end (oneand half year after baseline) of the intervention course. Mixed linear model was usedto analyse effects of the intervention.Results (1) Of286subjects were observed with average13.1±0.6years old.(2) Atbaseline, there were no significant differences between four groups in age, height,weight, BMI, total body BMC, BMD, BA and physical activity (P>0.05); There wereslightly significant differences between groups in daily energy, carbohydrate, fe,vitamin E intakes and pubertal development stages;(3) After intervention, there wereno significant differences in boys and girls between groups in height and incease inheight at the metaphase and the end. There was significant difference in height ofboys after adjusting possible basied factors (P=0.0359), but not for girls’ height. Afteradjustment of possible basied factors, there was intervention effect in boys’ weight butnot significant (P=0.0621). Girls’ weight had no significant intervention effect, andthe same results were found in increases in BMI of boys and girls at the metaphaseand the end. After adjusting for possible basied factors, there was significant groupeffect in girls’ BMI (P=0.045), but not for boys’. There were no significantintervention effects in BMI of boys and girls. After adjusting for possible baisedfactors, there were no significant group effects, time effects and intervention effects inlean body weight, body fat, percent of body fat of boys; There were significant timeeffects in lean body weight, body fat, percent of body fat of girls (P<0.05); There wasintervention effect in lean body weight but not significant (P=0.1081); There were nosignificant intervention effects in body fat and percent of body fat.(4) After adjustingfor possible basied factors, there was significant time effect in total BMC of boys(P<0.05), but no significant intervention effect (P=0.0916); For girls’ increase in totalBMC at metaphase, the a group (241.0g) and b group (213.1g) were higher thancontrol group (176.3g) by36.7%and20.9%, the c group (171.5g), however, was lessthan control group by2.7%(P=0.0422); For girls’ increase in total BMC at end, the agroup (327.7g) and b group (308.7g) were higher than control group (251g) by 30.6%and23.0%, the c group (244.4g), however, was less than control group by2.7%(P=0.0692); There was significant time effect (P<0.0001), but no significantintervention effect (P=0.1919);(5) For boys’ increase in total BMD at metaphase, thea group (0.042g/cm2), b group (0.037g/cm2) and c group (0.049g/cm2) were higherthan control group (0.033g/cm2) by27.3%,12.1%and48.5%,(P>0.05); Afteradjusting for possible baised factors, for boys’ increase in total BMD at metaphase,the a group (0.047g/cm2) and c group (0.051g/cm2) were higher than control group(0.038g/cm2) by23.7%and34.2%, the c group was the same as the control group;For boys’ increase in total BMD at the end, the a group (0.078g/cm2) and b group(0.071g/cm2) were less than control group (0.081g/cm2) by3.7%and12.3%, the cgroup was the same as the control. Overall, there was significant intervention effect intotal body BMD of boys after adjusting for possible baised factors (P=0.0187).(6)For girls’ increase in total BMD at metaphase, the a group (0.050g/cm2) and b group(0.042g/cm2) were higher than control group (0.033g/cm2) by51.5%and27.3%, thec group (0.029g/cm2), however, was less than control group by12.1%(P=0.0625);For girls’ increase in total BMD at the end, the a group (0.082g/cm2) and b group(0.069g/cm2) were higher than control group (0.054g/cm2) by51.9%and27.8%, thec group (0.051g/cm2), however, was less than control group by5.6%(P=0.0074);After adjusting for possible baised factors, for girls’ increase in total body BMD atmetaphase, the a group (0.050g/cm2) and b group (0.041g/cm2) were higher thancontrol group (0.033g/cm2) by51.5%and24.2%, the c group (0.029g/cm2), however,was less than control group by12.1%. For girls’ increase in total BMD at the end, thea group (0.081g/cm2), b group (0.068g/cm2) and c group (0.057g/cm2) were higherthan control group (0.054g/cm2) by50%,25.9%and5.6%. Overall, there wassignificant intervention effect in total body BMD of girls after adjusting for possiblebaised factors (P=0.0307).(7) After adjusting for baised factors, there were significanttime effect in BAP and TRAP-5b of boys and girls, IGF-1of boys and PTH of girls(P<0.05); There were no significant group effects in all biochemical indicators ofboys and girls; There were significant intervention effects in IGR-1(P=0.0125) andPTH (P=0.0348) of boys, but not for all biochemical indicators of girls. Conclusions Average daily calcium intake was lower in adolescents of district ofBeijing, it could enhance BMC and BMD of boys and girls to supply milk powderfortified with calcium, and it had a certain of effect on their nutritious status, but notsignificant for their height and weight; It was suggested that enough physical activityand increased calcium intake were needed to fulfil their development and growth ofconstitution. |
