Growth And Regulation Of Bone In Pubertal Girls

Purpose:The two year follow-up study aimed to investigate growth patterns of bone, and its correlations with serum estradiol, IGF-I and muscle strains as well as the effect of physical activity on bone growth in Finnish pubertal girls. Methods:The study population comprised 258 healthy Finnish girls aged 10-13 years at Tanner stage I-III maturational status at the time of recruitment. Bone geometry/density was measured annually: at baseline, and at 1-, and 2-years follow-up:①Body height (H) and body weight (W) were measured by electronic stadiometer every six months.②Body fat mass (FM) and lean mass (LM) together with whole body areal bone mineral density (aBMD), bone mineral content (BMC) and bone area (BA) were determined by dual energy X-ray absorptionometry (DEXA).③Tibial and raial, together with the cortical and trabecular bone, volumetric bone mineral density (vBMD), BMC, bone cross-sectional area (BCSA) and lower leg muscle mass (MM) were measured by peripheral quantitative computed tomography (pQCT).④Serum estradiol (E2) and IGF-I were assayed by fluoimmunoassay and radioimmunoassay, respectively.⑤The levels of physical activity of girls were determined by questionnaire. Menarche date was collected by questionnaire or retrospective phone call. The pubertal development was assayed by nurses according to the Tanner Stages published by Marshal and Tanner in 1969.Results:1. The changes of general characteristics: The average age of menarche was 12.9 years. The increment of body height was about 10 centimeters, with the body weight increasing 8.8 kilograms from pre-puberty to menarche. The FM, LM and MM increased significantly as well. The total body aBMD, BMC and BA increased with the age accrual and the increment of tibial vBMD exceeded the increment of radial vBMD significantly, without any patent difference in BMC and BCSA between tibia and radius. The tibial cortical bone grew about 0.38 centimeter during this period. Serum estradiol and IGF-I gained about 49% and 74%, respectively.2. The growth and growth velocity models:⑴Growth models of H, W, FM and LM: After entering puberty, growth of H and W was significantly, but W continued to increase and H slowed down its growth speed. The peak height velocity (PHV) was attained 14 months prior to menarche about 11.7 years, and the highest growth velocity of W was 5 months before menarche, which indicated that the H preceded W to reach highest growth velocity about 9 months. During the whole puberty, FM increased constantly while the main increment of LM was before menarche.⑵Growth and growth velocity models of radial vBMD, BMC and BCSA: Up to menarche, the radial vBMD continually decreased with lowest growth velocity about 27 months prior to menarche, averaging 10.6 years. It did not show increment until 6 months before menarche. With very high growth speed before menarche, BMC continued to increase and reached highest growth velocity about 2 months after menarche(average age13.1 years), while BCSA attained its highest growth velocity about 9 months before menarche (average age12.1 years) indicating BMC lag behind BCSA to reach highest growth velocity about 1 year.⑶Growth and growth velocity models of tibial vBMD, BMC and BCSA: The tibial vBMD increased continually without attaining its highest growth velocity during experiment. Tibial BCSA reached its highest growth velocity about 17 months prior to menarche (average age 11.5 years) with 20 months preceding BMC which attained its highest growth velocity about 3 months after menarche.⑷Growth models of estradiol and IGF-I: From pre-puberty to menarche, serum estradiol and IGF-I promoted their secretion and reached their individual's highest concentration near after menarche.3. Correlation:⑴Longitudinal relationships between serum IGF-I, E2 and LM, and whole body aBMD, BMC and BCSA: After adjustment for pubertal growth effect, serum IGF-I significantly correlated with aBMD (r=0.36, p<0.001), BMC (r=0.36, p<0.001) and BA (r=0.32, p<0.001), while erum E2 associated with whole body aBMD (r=0.18, p<0.01)and BMC (r=0.17, p<0.01) before menarche. Serum IGF-I correlated to BA only, without any relationship between E2 with aBMD, BMC and BA after menarche。Both before and after menarche,LM significantly correlated with whole body aBMD, BMC and BA (BM: r=0.44, p<0.001; r=0.78, p<0.001; r=0.74, p<0.001,AM: r=0.18, p<0.01; r=0.29, p<0.001; r=0.29, p<0.001)。⑵Longitudinal relationships between serum IGF-I, E2 and MM, and whole body aBMD, BMC and BCSA: After adjustment for pubertal growth effect, serum IGF-I significantly correlated with tibial BMC (r=0.31, p<0.001) and BCSA (r=0.25, p<0.01),while serum E2 associated with tibial BMC (r=0.19, p<0.01) and BCSA (r=0.15, p<0.05) before menarche. After menarche, however, both serum IGF-I and E2 did not show significant relationship with vBMD,BMC and BCSA。MM correlated to tibial vBMD,BMC and BCSA (r=0.21, p<0.001; r=0.79, p<0.001; r=0.75, p<0.001) before menarche,but MM associated with tibial BMC,BCSA (r=0.72, p<0.001; r=0.70, p<0.001) only after menarche,without any association of MM with vBMD。4. Effect of physical activity on bone growth: There were no differences in H, W, FM, LM, aBMD, BMC, and BCSA between low physical activity and high physical activity at baseline. After two year's development, significant differences in whole body aBMD(p=0.002,t=3.134),BMC(p=0.023,t=2.265) and LM(p=0.028,t = 2.186) were found between the two groups,but there were no differences in BA and serum IGF-I and E2。Conclusions:①Puberty was crucial period for girl development during which girls gradually attained physical and physiological maturation.②W lagged behind H to reach the highest growth velocity about 9 months during puberty, which suggested that the immune system may be weaken during this period.③Radial vBMD continued to decrease up to menarche and reached the lowest growth velocity about 27 months prior to menarche, which suggested that radius had a weak period during grow spurt which may be the key factors causing radius fracture.④Tibial vBMD continued to increase during puberty unlike radial vBMD indicating the the mechanical load promotes bone mineral accumulation. The asynchrony between growth of tiabial BMC and BCSA suggested that the weak bone during pubertal growth spurt can not be recovered by mechanical load.⑤The association of serum E2 and IGF-I with whole body aBMD before menarche suggested that the two hormones promoted the bone formation during puberty. No significant correlation between the two hormones and aBMD and vBMD after menarche indicated that other factors may be contribution to bone formation.⑥Serum E2 and IGF-I associated with whole body and tibial BMC mainly as the result of both increase of BMD and bone size before menarche, and no such association after menarche suggested that other factors were more important for BMC accrual.⑦Serum E2 mediates the bone formation mainly by depressing the marrow cavity and the anomalous bones have not marrow cavity so serum E2 only associated with tibial bone size but not whole body bone area.⑧LM and MM were the determinants of whole body and local bone formation and mineralization during pubertal growth.⑨Pubertal bone growth benefit from physical activity, and it act the function by mechanical mechanism but not system endocrine.