Boys are entering puberty earlier than previously thought, according to research from the United States recently published in the journal Pediatrics.

The largest study of its type, enrolling 4,131 healthy boys between six and 16 years of age with broad geographical representation, provides evidence that male puberty begins in the general population around ten or 11 years of age. That’s six to 24 months earlier than what was understood from studies undertaken 40 to 50 years ago.

Puberty in boys is driven by a sudden and sustained increase in the hormone testosterone. Testosterone prepares the testis to produce sperm and causes development of secondary sexual characteristics, such as pubic and facial hair and vocal deepening. Boys who develop elevated testosterone and associated features much earlier than their peers may experience significant and long-term social and educational challenges emerging from peer group and physiological pressures.

The researchers recorded distinct differences between African American, Hispanic and Caucasian (“white”) boys in the age of puberty onset. They found that one in five African American boys as young as six years old have visible signs of development, such as pubic hair and testis growth. Differences in pubertal timing between ethnic groups suggest that genetics underlie at least part of the biology of puberty.

Research has provided basic knowledge about which physiological processes control the timing of pubertal initiation but many aspects of this process are still only poorly understood. Some progress has recently been made in identifying candidate genetic factors, including our recent report on the timing of testis development.

We found that the process is explicitly dependent on a protein that conveys information from outside of the cell to the genes, switching them on or off. In unravelling this complex story, we discovered that testis development occurs earlier when the level of the protein in question is reduced, but development is delayed when it’s absent.

Importantly, these differences in developmental timing occurred without measurable changes in reproductive hormones. This suggests that testis maturation is not solely under the control of the hormonal axis. How an individual’s genetic make-up, the environmental factors they are exposed to and the interaction between these influence the timing of puberty and pace of puberty are important targets for future research.

The central outcome of the US study is that the average age of pubertal onset in boys is around ten to 11 years of age, earlier than the current clinical definition of normal puberty. This has immediate relevance to the management of boys’ health – health-care providers must recalibrate what is considered “normal”.

Early (precocious) puberty may arise from serious medical conditions, such as testicular or pituitary tumours that require treatment. But the redefinition of the age of pubertal onset is of much greater relevance to boys with delayed puberty.

Testosterone not only drives puberty but is also important for normal bone and muscle development. Delayed puberty results in lower bone density in adulthood, placing these men at increased risk of developing osteoporosis. This means reduced quality of life and significant social and health-care burdens. Timely testosterone treatment of boys with delayed puberty would promote bone growth, so that these boys may achieve normal bone density and strength in adulthood.

Another immediate impact of this study relates to the diagnosis and treatment of boys with Klinefelter syndrome. This condition, arising from the presence of an extra X chromosome, affects around one in 580 males and is characterised by under development of the testes and low-to-absent testosterone.

Boys with Klinefelter syndrome aren’t obviously distinguishable from other boys during infancy and early childhood, so it’s the delay or absence of puberty due to insufficient testosterone production that precipitates diagnosis. The associated features of this condition, which can include a lack of physical coordination, behavioural and learning difficulties and poor muscle and bone strength, can be minimised with early diagnosis, medical intervention and educational support.

Unfortunately, because of the inert nature of Klinefelter syndrome during early years, many boys are not diagnosed until well into their teens. The major challenge for health professionals is to identify these boys early enough to put interventions in place that will support their health, educational and social development. Formal recognition that puberty in boys occurs between ten and 11 years will increase the chance of earlier diagnosis for these boys.

There’s also an intriguing hint in this paper that socioeconomic factors may also influence the timing of puberty. In the study population, 80% of white boys had medical insurance, compared to one-third of African American boys. This raises a question about whether pubertal timing reflects socioeconomic conditions, which affect nutrition, health status and other lifestyle factors.

This benchmark paper provides the impetus to revisit the nature versus nurture debate to discover what controls human reproductive health.