Are kids experiencing puberty earlier in life?

Charles sent this question into The Naked Scientists on Facebook. Izzie Clarke was joined by reproductive physiologist Bill Colledge, from the University of Cambridge, who took us through the history of puberty.

Bill - Yes, they are. If you look historically at the age at which, particularly girls, first start going through puberty - and usually this is measured by their first period - in 1850, let's go back to 1850, it was about 17 years old. By 2010 it’s 12 years old. So there's definitely been a decrease in the age at which children go through puberty.

Izzie - And do we know why that is?

Bill - Well, partly this is caused by better nutrition, so people are better fed now. Certainly from 1850 onwards we've got better nutrition. And what is happening is people are growing more rapidly, they're gaining a critical body mass, and you have to achieve a critical body mass to go through puberty. But importantly, is not just about how much you weigh, it's about how much fat you carry in your body. And it's thought you have to have about 17% of your total body mass as fat to go through puberty, and you've got to have about 22% of your total body mass as fat to maintain fertility, and if you fall below those you either won't go through puberty or you will become sub-fertile. Top athletes that have less than 5% body fat, the females often don't cycle, they don't menstruate, they're infertile, because they have less body fat.

So what we think is happening with the Western diet of course, children are perhaps becoming obese, they're carrying a lot of body fat at a much earlier age, and this means they're actually going through puberty at an earlier age.

Izzie - Does that impact your life later on?

Bill - It can do, yes. It can increase the risk of developing certain types of cancer - ovarian cancers - because as soon as you go through puberty you start making all the various female hormones, and you are having a longer exposure to those over your lifetime. So it does increase the risk of some types of cancer.