BANGOR, Maine (WABI) - Pediatric specialists have noted over the past decade that both boys and girls are having the onset of puberty earlier than what the medical textbooks originally said. In the USA, it is generally taught that puberty begins for the average boy between 11 and 12 years old, which is about one year later than the age at which the majority of girls begin the process. The phenomenon of younger puberty in girls has been thought to be associated with increased childhood weight, as fat cells can have estrogenic metabolic effects on young girls.
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Conversely it has long been observed that girls who are underweight tend to have sexual maturity later than their peers. Boys have shown the same pattern of earlier puberty but were not thought to be as susceptible to the metabolic effects of being overweight. However, in a large Swedish study reported in the Journal of the American Medical Assn (JAMA Pediatr.doi:10.1001/jamapediatrics2019.2315), researchers have now demonstrated a similar trend for adolescent boys.
Researchers in the Swedish city of Gothenburg looked back at the school height and weight records of over 4,000 boys, going back to 1947 and for accuracy correlated the results for these same boys at the time of conscription into the military at age 18, which was mandatory in Sweden until 1996. Because boys do not have a specific event to indicate the onset of adolescence as girls have with menstruation, they chose the marker of 'peak height velocity' (PHV) instead. What they found was that as the average BMI (body mass index) increased for these young men over the decades, their maximum growth spurt occurred at an earlier and earlier age. Specifically they found that for each decade of the 50 year interval studied, the PHV was 1.2 months earlier than the previous, so that at the end of the study for these young boys in Sweden, they were on average having this marker of puberty 6 months earlier than those at the beginning of the study.
The researchers commented on the health implications of this trend, which can result in more young adults developing diabetes and other chronic medical conditions associated with being overweight. Also there is the known fact that both boys and girls who have early puberty will be on average, shorter and heavier than their peers. In addition, there are interesting behavioral consequences of earlier puberty. Girls show more emotional disturbances with lower self-esteem, and earlier pregnancy rates which in turn can decrease school performance and affect economic self-sufficiency rates. Boys actually have higher self-esteem scores in early adolescence as they are usually better at athletics compared with peers due the effects of testosterone, but they also show higher rates of social delinquency and substance use.
The authors were quick to point out other factors that can influence onset of puberty, including the exposure to hormone-active chemicals found in many household products and in the food chain. These endocrine disrupter ccompounds, such as bisphenol A (BPA) and phthalates, have estrogenic effects that can contribute to earlier puberty in girls as weight gain. Although there are many factors, including genetics that influence the onset of puberty, experts agree that we should all strive to avoid these contaminants and work at keeping a healthy BMI for many reasons. Childhood is a unique and very precious time in the lives of human beings, and there is no need to rush the next generation toward adulthood. Goodness knows, they will get there soon enough.
(1)JAMA Pediatr. doi:10.1001/jamapediatrics.2019.2315