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 Pediatrics, 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.
What is puberty?
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 psychological health problems, 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.
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 childhood obesity, being born small for gestational age and exposure to environmental chemicals. Other researchers have linked early puberty with living with a stepfather or having experienced stressful life events, 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 later than normal, a UK study found girls who grew up the poorest were twice as likely to have started their periods earlier 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 Growing Up in Australia Study 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 ten to 11 years old, about 19% of boys and 21% 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.
How could this happen?
Research on the biology of stress 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 suggests the social environment can influence so-called epigenetic changes in our genes. These changes might affect the regulation of genes involved in reproductive development, switching some on or off sooner than usual.
Another theory is that in the face of hardship – 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
What we do know, however, is early puberty is linked with a range of health issues.
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 greater risk of developing obesity, reproductive cancers and cardiometabolic diseases (diabetes, heart disease or stroke) in later life.