50-year study of boys illustrates long-term trend towards earlier puberty

medwireNews: A Swedish study suggests that, as with girls, puberty has shifted to begin at an earlier age in boys.

However, the authors of an editorial accompanying the publication in JAMA Pediatrics believe the overall evidence suggests that “the normal curve for male puberty may be changing in shape rather than simply shifting symmetrically to younger ages.”

The researchers – Maria Bygdell (Sahlgrenska Academy at University of Gothenburg, Sweden) and colleagues – used peak height velocity (PHV) during the pubertal growth spurt as a surrogate for puberty in 4090 Swedish boys between 1947 and 1996, finding that this occurred at an average age of 13.9 years.

Each decade increase in date was associated with a 1.5-month reduction in the boys’ average age at PHV, suggesting that puberty shifted to a younger onset age during the study period. The researchers found that age at PHV also decreased with increasing BMI at age 8 years, which itself increased over time, and the association between age at PHV and date was attenuated after accounting for BMI, indicating that this contributed to the association.

But it did not account for all of it; there remained a significant 1.2-month reduction per decade increase.

The effect of date on age at PHV was most striking for boys with late puberty. Not accounting for BMI, those in the 90–100th percentile of age at puberty onset had a 1.49-month reduction in onset age per decade date increase, whereas those in the 0–10th percentile had a 0.73-month reduction.

“Thus, the data suggest that the trend toward earlier average puberty in the Swedish population is driven more by a reduction in boys who experience puberty later than an increase in those who experience it earlier”, write editorialists Vanessa Curtis (University of Iowa, Iowa City, USA) and David Allen (University of Wisconsin, Madison, USA).

They say that this is in line with data in girls.

“The change in distribution of pubertal timing may be associated with improved living conditions and reduced rates of malnutrition, allowing children to progress into and through puberty as programmed with fewer interfering factors without necessarily indicating that the lower end of the normal range of puberty onset for males needs to be reconsidered”, they write.

Curtis and Allen caution that PHV is a surrogate marker of puberty and that the study assumes that the relationship between PHV and age at puberty has remained constant over 50 years. And they add that despite the increasing BMI over time in this Swedish population, the boys’ BMIs remained relatively low and homogenous relative to those in other populations, such as the USA.

“Thus, the association between BMI and pubertal timing described in the article can only be cautiously extrapolated to a heavier and more heterogeneous population”, they conclude.

By Eleanor McDermid

medwireNews is an independent medical news service provided by Springer Healthcare. © 2019 Springer Healthcare part of the Springer Nature group

JAMA Pediatr 2019; doi:10.1001/jamapediatrics.2019.2315
JAMA Pediatr 2019; doi:10.1001/jamapediatrics.2019.2306
Martin Savage
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