medwireNews: Longitudinal study findings support a relationship between body mass index (BMI) and the timing of puberty in boys, with a link found between obesity and precocious gonadarche (PG).
“Early puberty worsens the comorbidities associated with obesity and early puberty might increase the risk of behavior problems”, say Veronica Mericq, from the University of Chile in Santiago, and co-authors in The Journal of Clinical Endocrinology & Metabolism.
Noting that precocious puberty in boys has also been linked to an increased risk of prostate cancer and cardiovascular disease in adulthood, they postulate “that controlling the increases in BMI SDS [standard deviation score] throughout childhood could be useful in decreasing these risks.”
The team collated information from the Growth and Obesity Chilean Cohort Study for 494 boys who entered the study in 2006 at age 3.0–4.9 years old. The participants all had a gestational age of 37–42 weeks, a birth weight of 2500–4500 g, and no physical or psychological conditions that affect growth, the researchers explain.
The boys underwent annual measurements of body composition and hormone levels, and semi-annual visits to assess for secondary sex characteristics began in 2009 around age 7 years. Age at gonadarche onset was determined as the midpoint between the last visit without an increase in testicular size and the first visit where signs of sexual development were detected.
The researchers report an increase in BMI SDS, total obesity (BMI SDS ≥2) and central obesity (waist circumference ≥90th centile of Mexican population) throughout childhood, with values of 0.96 SDS, 15.1% and 6.3%, respectively, at age 4–5 years, increasing to a corresponding 1.00 SDS, 22.7% and 11.6% at the last visit before gonadarche.
Overall, 45 boys were diagnosed with PG, defined as having a testicular volume of at least 4 mL before the age of 9 years. Compared with boys without PG, these participants had higher weights at birth and throughout childhood and were more likely to be obese from age 2 years onwards, as well having a higher percentage of fat and central obesity from age 4 years.
Moreover, higher BMI SDS at any age was “associated strongly” with the likelihood of PG, even after considering maternal education, and BMI SDS at birth and at previous study visits, say Mericq et al.
Boys who were obese at age 2–5 years or 6–7 years were more likely to develop PG than their non-obese counterparts, as were those with versus without central obesity at age 6–7 years, and a similar relationship was also identified between fat mass percentage at 4–7 years and increasing risk of PG.
BMI z-scores at age 4–5, 5–6 and 6–7 years all had a “strong positive association” with PG, with odds ratios of 2.1, 1.8 and 1.5, respectively, after adjusting for birth BMI and rate of BMI change between 0–2 years, the researchers say.
Conversely, there was a negative correlation between age at testicular enlargement and average BMI, BMI SDS at birth and BMI SDS at age 4 years.
Boys who had a normal BMI at age 2–7 years experienced testicular enlargement at an average age of 11.17 years versus 10.8 years for those with an overweight BMI during childhood and 10.72 years for those with an obese BMI.
Noting that puberty has been proposed as the cause of obesity, perhaps through changes in oestradiol levels, the researchers emphasise that their “longitudinal analysis precludes this reverse causality; we detected first increase in adiposity and next gonadarche”.
The team concludes: “Future research is necessary to understand the bidirectional relationship between obesity and puberty, and whether obesity shift[s] the normal mean ages of pubertal maturation in boys.”
By Lynda Williams
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