A Follow-up Study Of Relationship Between Pubertal Timing And Physical Development During Adolescence

Objective:The purpose of this prospective cohort study was to clarify the relationship between pubertal timing and physical development during and around adolescence (before the onset of puberty, early adolescence, rapid development period of adolescence and late adolescence), and to provide scientific evidence for the lifelong health effect of pubertal timing as well as physical development during adolescence.Methods:A baseline survey was conducted in October2010among boys and girls in Shanghai selected by stratified cluster sampling method, including two elementary schools, two middle schools and two high schools selected from an urban district and a rural district, respectively. Classes were considered as sampling units according to the sampling frame of the Chinese Student’s Physical health research, in order to ensure that there were about75boys and75girls in each grade. Participants who had congenital malformations, genetic or metabolic disease or endocrine system chronic disease were removed from the sample. A follow-up survey was conducted in May2012among those who had participated in the baseline survey as well as coming from the rural district, including grade two to five in elementary school, grade one to three in middle school and grade two to three in high school. Both baseline and follow-up survey measured pubertal development stages (including breast, pubic hair and armpit hair development stage in girls, bilateral testicular volume, external genitalia, pubic hair, armpit hair and beard development stage in boys, respectively) as well as physique and body fat level (including height, weight, waist circumference, hip circumference, triceps skinfold thickness and subscapular skinfold thickness). For each participant, information about socio-demographic data, the status of menarche/spermarche, birth weight, gestational weeks, mother’s age of menarche, diet and exercise during the period of investigation were recorded.Results:A total of3462boys and girls were involved in the baseline survey, aging from6to20years old. Of the821boys (54.2%) and693girls (45.8%) who came from the urban district, the average age of all subjects was12.44±3.58. Of the966boys (49.6%) and982girls (50.4%) who came from the rural district, the average age of all subjects was12.10±3.48. A total of1306boys and girls participated in the follow-up survey, including620boys and686girls aging from6to18years old, with a mean age of11.34±3.20at baseline. The changes of main physique and body fat indicators with age and pubertal stages were analyzed using the baseline data. It was found that BMI increased with increasing age both in boys and girls; waist-to-hip ratio decreased slightly with increasing age, but remained stable; body fat percentage (%BF) increased with increasing age before the age of10, then gradually decreased when boys entered into early adolescence;%BF increased with increasing age in girls, which showed a significant gender difference of%BF development after entering into adolescence. For boys, when using testicle development stage as pubertal stage, it was found that BMI increased with pubertal stages, while waist-to-hip ratio decreased, boys whose testicular development had reached stage Ⅱ had higher%BF than those who stayed in stage Ⅰ,%BF then decreased as pubertal stages increased. For girls, when using breast Tanner stage as pubertal stage, it was found that BMI and%BF increased with pubertal stages, while waist-to-hip ratio decreased, but increased when entering into stage V.Mean age at entry into each pubertal stage was calculated by probit analysis. For boys, media age of onset of testicle, external genitalia, pubic hair, armpit hair and beard development were10.71years,11.68years,12.57years,14.07years and15.11years, respectively. And median age of spermarche was16.63years. It lasted3.26years,4.87years and4.35years for testicle, external genitalia and pubic hair respectively, from onset of pubertal development to mature. For girls, media age of onset of breast, pubic hair and armpit hair development were8.26years,11.48years and11.71years, respectively. And median age of menarche was12.09years. It lasted8.38years,7.59years and2.68years for breast, pubic hair and armpit hair respectively, from onset of pubertal development to mature.For those who hadn’t started puberty at baseline, independent impact of each indicator of pre-adolescence physique and body fat on the earlier onset of puberty ("whether testicular volume is4ml or greater" in boys and "whether breast development have reached Tanner stage Ⅱ" in girls, respectively) was examined by using binary logistic regression analysis with the covariation effect of age at baseline, birth weight, gestational weeks, mother’s age at menarche, diet and exercise during the period of investigation being controlled. Odds ratio of pre-pubertal height and weight toward early pubertal timing were1.120(1.025-1.225) and1.076(1.008-1.148) in boys, respectivly, which indicated that boys who had higher level of pre-pubertal height or weight would more like to start puberty earlier. Odds ratio of pre-pubertal height, weight, BMI, waist circumference, hip circumference and subscapular skinfold thickness toward early pubertal timing were1.124(1.017～1.243),1.910(1.051～1.347),1.299(1.018～1.657),1.156(1.040～1.284),1.166(1.054～1.289) and1.272(1.041～1.555) in girls, respectively, which indicated that children who had higher level of pre-pubertal height, weight, BMI, waist circumference, hip circumference or subscapular skinfold thickness would more likely to start puberty earlier.For participants who had started puberty at baseline, testicular volume and breast Tanner stage were considered as pubertal development level for boys and girls, respectively. Those who were in early adolescence (10to11years old in boys and6to8years old in girls, respectively) were devided into "early pubertal timing" and "delayed pubertal timing" according to "whether testicular volume was4ml or greater" in boys and "whether breast development had reached Tanner stage II" in girls, respectively. Those who were in late adolescence (15to17years old in boys and14to18years old in girls, respectively) were divided into "early pubertal timing" and "delayed pubertal timing" according to "whether testicular volume was20ml or greater" in boys and "whether breast development had reached Tanner stage V" in girls, respectively. Finally, those who were in the rapid development period of adolescence (12to14years old in boys and9to13years old in girls, respectively) were divided into "early pubertal timing","on-time pubertal timing" and "delayed pubertal timing" according to the P25and P75age at entry into each pubertal stage (testicle development stage for boys and breast Tanner stage for girls, respectively). Impact of pubertal timing on physique and body fat changes in different stages of pubertal development was examined by using multiple linear regression with the covriation effect of age at baseline, physique and body fat level at baseline, diet and exercise during the period of investigation being controlled. For boys, it was found that height increment during early adolescence was significantly higher for the participants of early pubertal timing than those of delayed pubertal timing (0.585cm, t=3.281, P=0.002). For girls, height increment during the rapid development period of adolescence was significantly lower for the participants of early pubertal timing than those of on-time pubertal timing (0.151cm, t=-3.624, P<0.001), besides, triceps skinfold thickness increment, subscapular skinfold thickness increment and%BF increment during late adolescence were significantly higher (0.175mm, t=2.056, P=0.042;0.191mm, t=2.215, P=0.028;0.191, t=2.283, P=0.024, respectively) for the participants of early pubertal timing than those of delayed pubertal timing.Conclusion:It’s found that in comparison to those living in cities of middle or western China and some other countries, boys in Shanghai start pubertal development a little bit later, and the progress of sexual development is also relatively slower, median age of spermarche is being postponed. Besides, onset of breast development of girls in Shanghai is relatively earlier, with onset of pubic hair being later and the progress of sexual development being slower, further dynamic observational study of secular change of menarche age is needed. Boys who have higher level of pre-pubertal physique and girls who have higher level of pre-pubertal physique or body fat would more likely to start puberty earlier. Early pubertal timing will result in higher level of height and height increment for boys in early adolescence, as well as higher level of body fat and body fat increment for girls in late adolescence.