Study On Relationship Between Pubertal Timing And Development Of Obesity In Childhood And Adolescence

Objective:To use growth spurt indicators to define pubertal timing and provide methodological evidence for the future study of health hazards of advanced pubertal timing based on large population. To study the growth pattern of peri-pubertal body fat mass in relating to pubertal timing among children and adolescents and provide epidemiology evidence for basic research of pubertal mechanism and obesity prevention and control.Methods:A total of 329 students in grade 9 were selected from 3 schools in Shanghai. For every subject, annual checkups of height and weight in past nine years were obtained from school health profile. Subject inclusion criteria consisted of date of birth, at least physical test records during the past 9 years and at least once height and weight checkups for girls before age 8 and boys before 9 in these 7 schools. Cubic spline fit function was used to calculate age at the onset of growth spurt and age at the peak height velocity which were defined as the indicators of pubertal timing. BMI-Z score at pre-puberty, at early puberty, and at middle/late puberty were analyzed relating to pubertal timing, meanwhile amount of BMI-Z increment at early and at middle/late puberty was compared between different groups of pubertal timing.Results:Of the 142 boys (43.2%) and 187 girls (56.8%) participating in the study, the average age of all subjects was 15.09+0.32. In grade 9, BMI score of boys and girls was 20.00±3.83kg/m2 and 19.20±2.69kg/m2, respectively. Average age at onset of growth spurt was 10.72±1.10 and 9.15±1.08 in boys and girls, respectively. Age at peak height velocity was 12.97±0.95 and 11.02±1.24. Peak height velocity was 10.13±1.48 cm/year and 8.62±1.63 cm/year. Pubertal duration lasted 2.26±0.84 years and 1.96±0.83 years, while first spcrmatorrhea age among boys and menarchc age among girls was 15.09±1.70 and 13.95±1.10, respectively. Therefore, different stage of puberty could be defined accordingly. In grade 1, average age of boys'was 7.11±0.33 years old, while girls'was 7.07±0.32 years old. All subjects didn't start growth spurt. So that BMI1 and BMI-Z 1 were used to indicate pre-pubertal body fat mass. In grade 5, girls'average age was 11.07±0.32 years old and most of them started growth spurt and reached peak height. In grade 6, boys'average age was 12.11±0.33 years old and most of them were experiencing peak height velocity. So, BMI5/6 and BMI-Z5/6 was used to indicate body fat mass of early puberty. In grade 9, girls' average age was 15.07±0.32 years old, in which 84.7% of them had had menarche; the average age of boys was 15.11±0.33 years old, in which 93.1% of them had experienced peak height velocity. So, BMI9 and BMI-Z9 was used to stand for their body fat mass of middle-late puberty. Thus, the difference between BMI-Z1 and BMI-Z5 and the difference between BMI-Z5 and BMI-Z9 represented the amount of fat mass increment during early and middle-late puberty for girls, while the difference between BMI-Z1 and BMI-Z6, the difference between BMI-Z6 and BMI-Z9 represented the amount of fat mass increment during early and middle-late puberty for boys, respectively.Among various indicators that can be used to define pubertal timing, it was found that age at peak height velocity could reasonably classified all participants into three groups of pubertal timing as the earlier, the on-time, and the later. There was found a significant correlation between age at peak height velocity and age at first spermatorrhea/age at menarche, with Pearson coefficients being 0.204(P=0.028) for boys and 0.311(P<0.001) for girls, respectively. Therefore, in the subsequent analyses, age at peak height velocity was used as the indicator for categorization of pubertal timing.In girls, age at onset of growth spurt and age at peak height velocity was significantly earlier in higher peri-puberty BMI-Z group. In boys, although the similar trend still exited, only age at peak height velocity was significantly earlier in higher pre-puberty BMI-Z group. Age at menarche was relatively later in higher BMI-Z group, especially in early puberty. But the relationship between peri-puberty BMI-Z score and first spermatorrhea age was not clear. In both boys and girls, there was no significant difference in pubertal duration between different peri-puberty BMI-Z groups.Comparisons of fat mass increment between participants of earlier pubertal onset and non-earlier onset group by controlling for weight at grade 1 and self-perceived social-economic status were conducted. In girls, it was found that fat mass increment during early puberty was significantly higher for participants of earlier pubertal onset than those of non-earlier group, but the difference of fat mass increment during middle-late puberty was not significant between these two groups. In boys, there was not any statistically significance of fat mass increment during early puberty and middle-late puberty between two groups of earlier and non-earlier pubertal onset.Finally, independent impact of pre-pubertal body fat mass on the earlier onset of puberty was examined by using multiple logistic regression analysis with the co-variation effect of mothers'figure, mothers'education level and self-reporting family economic status being controlled. Odds ratio of pre-pubertal body fat towards advanced pubertal timing was 1.281 (1.017-1.614) and 1.281 (1.055-1.555) in boys and girls, respectively, which indicated that children who had higher level of pre-pubertal body fat mass would more like to start puberty earlier.Conclusion:Pre-pubertal body fat mass is a prominent factor that might lead to early onset of puberty. Higher level of BMI in pre-puberty and greater amount of BMI gain during early puberty may lead to higher level of BMI in adolescence as well as adulthood. Necessary intervention measures should be taken in stages of pre-puberty and early puberty in order to lower down prevalence rates of overweight and obesity in the whole population. Comprehensive health services, such as physical and psychological health care service, reproductive health care service should also be conducted for adolescents of advanced puberty. These strategies and measures would be helpful in promoting healthy growth of children, reducing social burden of chronic diseases and improving humans'quality of life.