Shape-shifting bodies. Cracking voices. Hairs sprouting in new places. Puberty marks a dramatic period of change for young people. Now new research shows children who grow up in poor homes enter puberty early. 
Not only do they experience more emotional, behavioural and social problems compared to their peers, early puberty puts them at risk of a range of health issues for the rest of their lives.
The research, published today in the journal , adds to a body of work showing the cumulative effect of adversity in childhood can have lifelong physical, mental and behavioural repercussions.
However, the reason why these disadvantaged children enter puberty early remains unclear. And work is continuing to pinpoint factors that trigger the cascade of hormones that mark this critical period of development.
Not only do they experience more emotional, behavioural and social problems compared to their peers, early puberty puts them at risk of a range of health issues for the rest of their lives.
Puberty is an inherently awkward transition in which a child’s body matures to allow reproduction.
In girls, it typically begins with breast development between the ages of eight and 13 and ends with menarche, or the first period. In boys, puberty begins between ages nine and 14, on average, starting with growth of the sexual organs and wrapping up with facial hair and a deepened voice.
But changes at puberty are not all physical. Puberty also triggers rapid biological and social change, and increasing risk for , like depression and anxiety, substance use and abuse, self-harm and eating disorders.
We still don’t know exactly what triggers the cascade of hormone secretions that, over time, produces these tell-tale changes. And “What triggers puberty?” was one of the 125 questions posed in Science magazine’s 125th anniversary edition in 2005 that still remains unanswered today.
Other researchers have linked early puberty with living with a stepfather or having experienced stressful life events, such as childhood maltreatment and abuse.
In particular, we still don’t know exactly what causes some children to enter puberty earlier than others, although there have been many factors linked to early puberty.
These include , being born and exposure to . Other researchers have linked early puberty with or having experienced , such as childhood maltreatment and abuse.
What we did
Previous studies looking into social impacts on the timing of puberty have had mixed results. While one Indian study found poor girls started their periods , a UK study found girls who grew up the poorest were twice as likely to have started their periods than the richest.
So, we carried out the first study of its kind in Australia to see how cumulative exposure to social disadvantage affected the age children entered puberty.
We asked parents of 3,700 children in the to report signs of their children’s puberty at age eight to nine, and then again at ten to 11. Signs included: a growth spurt, pubic hair and skin changes; breast growth and menstruation in girls; and voice deepening and facial hair in boys.
We then compared the family’s socioeconomic position – as measured by their parent’s annual income, education and employment – of those who started puberty early with others who started on time.
At 10-to-11 years old, about 19 per cent of boys and 21 per cent of girls were classified in the early puberty group. In other words, they had entered puberty earlier compared to their counterparts.
Boys from very disadvantaged homes had a four-fold increase in the rate of early puberty, while girls’ risk increased nearly two-fold compared with kids that came from the richest families.
What we do know, however, is early puberty is linked with a range of health issues.
How could this happen?
Research on the shows how major adversity, like extreme poverty, can permanently set the body’s stress response to high alert, affecting the brain’s circuits. This might, in turn, influence how reproductive hormones are regulated, so affecting the timing and trajectory of puberty.
Another body of research the social environment can influence so-called in our genes. These changes might affect the regulation of genes involved in reproductive development, switching some on or off sooner than usual.
Another is that in the – for instance, economic disadvantage, harsh physical environment, the absence of a father – children may be programmed to start the reproductive process earlier to ensure their genes are passed on to the next generation.
Yet, we still don’t know exactly how poverty or disadvantage triggers early puberty.
Why this matters
For instance, in girls, it’s linked with emotional, behavioural and social problems during adolescence including: depressive disorders, substance disorders, eating disorders and earlier-than-usual displays of sexuality.
Early puberty also affects people’s health far beyond their teenage years. It places them at a of developing obesity, reproductive cancers and cardiometabolic diseases (diabetes, heart disease or stroke) in later life.
, Associate Professor and Visiting Academic, Centre for Adolescent Health,
The new series of Struggle Street starts Tuesday 28 November 8.30pm on SBS.
A two-week event: Tuesday-Thursday.
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Struggle Street series two is produced by KEO Films with funding support from Screen Australia and Film Victoria.
All episodes of Struggle Street will be available to view on SBS On Demand after broadcast.
Episodes one, two and three will encore on Viceland on Friday 1 December from 8.30pm, while episodes four, five and six will encore on Viceland on Friday 8 December from 9pm.
NITV's The Point will host a special show to discuss the issues raised in the documentary on Wednesday 29 November 9.30pm.
The Feed Special will also air on Viceland on Friday 8 December at 8.30pm.
