When parents worry about their kids growing up too fast, they’re usually talking about kids’ social development, but in fact, many kids are growing up too early physically too.

Kids are now entering puberty at a much earlier age than their grandparents ever did, with researchers unable to fully explain why.

In the 1800s, teenagers typically reached puberty at around 15 or 16. Today, the average age of onset is 10 or 11, with some girls starting puberty as young as eight, and boys as young as nine.

The reasons behind the trend are still unclear, but Dr. Preetha Krishnamoorthy, a pediatric endocrinologist at Montreal Children’s Hospital, says it’s likely that diet and nutrition are big drivers.

“I believe it’s in large part due to our nutritional status,” she told CTV’s Canada AM Thursday from Montreal. “As we see that the overall trend in weight has gone up, that probably does have an effect on the onset of puberty.”

When doctors noticed the age of puberty shifting in the early 20th century, they attributed it to better health and nutrition. These days, childhood obesity is often blamed, since fat cells produce estrogen that could trigger puberty. But some studies have shown puberty is starting earlier in many parts of the developed world, regardless of a child’s weight.

Dr. Krishnamoorthy says it’s important to note that the average age that a girl gets her first period – the final stage of puberty – hasn’t changed much. First menstruation typically occurs between ages 12 and 13, as it has for decades.

What has changed is that puberty is starting sooner and the whole process is taking longer. The earliest stages – skin and body odour changes -- can begin anywhere after age eight in girls and nine in boys.

Are hormones to blame?

As for concerns that hormones in our food and water are causing kids to enter puberty sooner, Dr. Krishnamoorthy is not convinced. She says there is no good, reliable evidence that environmental chemicals are causing kids’ bodies to change.

“It’s hard to really know. But it seems that the amount of hormones in our food is probably negligible and not enough to account for the earlier trend of puberty,” she said.

Then there are the kids who experience “precocious puberty” -- meaning puberty before the age of 7 in girls, or age 8 or 9 in boys.

Early puberty can be devastating to kids who aren’t emotionally equipped to handle the changes. These kids often face bullying and isolation, and in some cases, they also have to deal with menstruation before they even fully understand it.

“That is one of the main reasons we look at treating early puberty,” says Dr. Krishnamoorthy.

Precocious puberty can be treated

The other reason to treat precocious puberty is that it causes children to have their growth spurt early and for their bones’ growth plates to close early. That effectively ends the child’s growth, leaving them shorter than their peers.

As for what triggers precocious puberty, Dr. Krishnamoorthy says that remains unknown. What is known is that precocious puberty is not more common now than in the past. True precocious puberty is still quite rare.

Nevertheless, parents should still see a doctor if they are concerned something is wrong with their child. In rare cases, it could be that a tumour or cyst near the pituitary gland or on an ovary or the testicles is causing hormonal changes.

When there is true activation of the pituitary gland in the brain too early, there are hormonal treatments that can halt the puberty.

The vast majority of the time, though, when parents bring their kids to see pediatric endocrinologists such as her, the changes they are seeing don’t need treatment at all, Dr. Krishnamoorthy says.

“Some of the kids who come in with early signs of puberty, it actually ends up being a complete variant of normal.”