Since the 1970s, the age of puberty has declined. Although the changes are incremental, they add up. From 1970 to 2013, the age of onset of puberty decreased by 0.24 years per decade and 50 years later, 6-year-olds begin to develop as adults.

A study published in Child development found that “stressful family relationships” influence girls’ early maturation. others research showed that child abuse can also play a role. Some evidence even suggests that stress during pregnancy can cause girls to develop at a younger age.

All this makes researchers wonder what will happen in the future. It’s already a stressful time for kids with the pandemic, school violence and an increasingly polarized society. Will all this stress force our children to grow up even younger?

A combination of factors

It’s a complex and nuanced situation, says Megan Gunnar, a child psychologist and professor at the University of Minnesota. Research is mixed, and it’s important to note that changes at the onset of puberty are mild. Although certain types of stress seem to cause the early onset of puberty, there are likely other forces at work. Obesity and weight gain in younger girls are also important drivers of development.

“Weight gain has a big impact on the onset of puberty,” says Gunnar.

Often the reasons are grey, not black and white. It’s not one thing. These are several factors that work together to motivate small changes. That seems to be happening here, says Gunnar.

Genetics, race and endocrine disrupting chemicals found in food and personal care products can also cause early puberty. And these things are hard to study. Researchers will need to control for factors such as diet to fully understand the true impact of stress on development.

“Nature does not give us clean buckets. When we’re stressed, we eat comfort foods, and when we eat comfort foods, it can lead to weight gain,” she says.

What happens in the brain?

What causes the change? How can a child’s development be altered by stress or obesity? According to Elizabeth Shirtcliffe, a professor of psychology at the University of Oregon, several factors are at play.

Psychosocial stress affects the limbic system of the brain, which is responsible for emotions. The limbic system then communicates with the hypothalamus, and this is where much of the pubertal changes occur because it is also the site of the gonadotropin-releasing hormone (GNRH) pulse generator.

During childhood, your brain actively inhibits GNRH from releasing puberty hormones like estrogen and testosterone, allowing children to experience childhood without hormones in the mix, Shirtcliff says.

“Inhibitory neurotransmitters like GABA stop puberty until GNRH starts releasing impulses from hormones like estrogen and testosterone, allowing the body to start developing. “The stress of things like abuse allows sex hormone impulses to flare up, and when that happens too often, the system breaks down and the child starts to develop early,” says Shirtcliffe.

Shirtcliff says that many of the stress hormones that are released when children experience psychosocial stress can also mimic sex hormones. This means that once puberty begins, it ends much more quickly than under normal circumstances.

“Instead of it being this slow, long process, it’s much faster because developing in a stressful context causes the hormones to come in very quickly,” says Shirtcliffe.

Hormonal changes happen in both boys and girls, but boys don’t have a cyclical pattern like girls (due to menstruation), says Shirtcliffe.

“When boys go through puberty, it comes in fits and starts, and we’re less likely to know when it’s going to happen,” she says.

But we know that stress in both boys and girls affects pathways in the brain responsible for development. Shirtcliffe says stress causes a “package of biological changes” that can lead to early puberty. Leptin, for example, which is linked to obesity, is also a “stress hormone”. All of this means that everything works together to shift development.

“It’s not just obesity and it’s not just psychosocial stress, these things go hand in hand, impacting early maturation,” says Shirtcliffe.

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