medwireNews: Overweight and obese boys have reduced testosterone levels and shorter penises during puberty than their normal-weight counterparts, study findings demonstrate in The Journal of Clinical Endocrinology & Metabolism.

“The possible significance of these observations for adult genital development and reproductive potential will require large longitudinal studies”, say Mario Mancini, from San Paolo Hospital in Milan, Italy, and co-authors.

They assessed anthropometric and genital development in 1130 boys aged from 0 to 20 years of age who were attending a paediatric andrology clinic with genital pain, varicocele, mobile testis or scrotal cysts.

The average age was 10.31 years in the 297 obese children and 9.60 years in the 833 normal-weight children.

There were notable differences in the ages at pubertal stages between the two BMI groups, such that obese children were older on average in Tanner stage P1 than normal-weight boys (8.2 vs 5.9 years) but significantly younger in stages P3 (12.4 vs 13.1 years) and P5 (15.1 vs 16.4 years).

“This suggests that puberty in obese young children in our study started later and evolved more rapidly in more advanced Tanner stages”, say Mancini et al.

In addition, obese boys had “slightly smaller” testes volume than normal-weight boys throughout puberty and approximately 50% lower testosterone levels, resulting in a “significantly weaker” correlation between age and testosterone level during puberty in obese vs normal-weight boys (r=0.59 vs 0.73).

And there was a significant and negative correlation between testosterone and BMI during puberty overall (r=–0.54) and at each pubertal phase.

“Considering the critical role of testosterone in penile development, it is not surprising that penis length in obese boys in the final [pubertal] stages was shorter than their normal weight counterparts”, the researchers write.

The team created a novel method of penis measurement where the flaccid penis is positioned perpendicular to the body against a rigid ruler without stretching. Measurement is taken from the pubic angle to the top of the glans and pubic fat is compressed by one end of the ruler, the researchers explain, thereby avoiding the risk of potential errors associated with the Schonfeld stretching technique.

This revealed that penile length was approximately 11% shorter in obese than normal-weight children, with an average deficit of 9.3 mm and 9.4 mm in obese boys at stages P4 (67.5 vs 76.8 mm) and P5 (76.8 vs 86.2 mm), respectively.

Obese and normal-weight children had a significant and positive correlation of comparable magnitude between testosterone levels and penis length (r=0.792 and 0.747, respectively) and stepwise multiple regression analysis indicated that penis length was significantly predicted by testosterone but no such relationship was found with BMI.

Mancini and co-authors therefore believe that “[o]besity may represent a major determinant reducing testosterone level and penis development.”

They conclude: “The possible predictivity of early penile measurements with our methods suitable for overweight children will require longitudinal studies.

“This could allow effective early nutritional or hormonal/pharmacological treatments for optimal genital development and possibly reproductive potential in obese children.”

By Lynda Williams

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J Clin Endocrinol Metab 2021; doi:10.1210/clinem/dgab535

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