So , we want to be very careful about leaping to conclusions about what these trends mean , but the trends themselves are very , very apparent . And as a final point , I should also mention that there are a number of different behavioral and psychosocial as they're called interactions that can influence puberty as well . This has been most strikingly observed in animals .
And that hormone leptin travels in the bloodstream across the blood brain barrier and goes to the hypothalamus and can trigger the onset of puberty by activating the neurons that release gonadotropin releasing hormone . So many people believe that one of the reasons that puberty is happening earlier and earlier in females is because of the accumulation of more body fat at younger ages than was observed 30 or 40 certainly 100 years ago . Now , I can already imagine a number of people are thinking , oh , this must re relate to the obesity crisis .
We know that one of the things that can trigger the onset of puberty , in particular in females is that when enough body fat accumulates that body fat releases a hormone called leptin . And that hormone leptin travels in the bloodstream across the blood brain barrier and goes to the hypothalamus and can trigger the onset of puberty by activating the neurons that release gonadotropin releasing hormone .
However , it could also be unrelated to obesity . It could be , for instance , improved nutrition and the avail availability of quality nutrition which can signal the maturation of the brain and body mechanisms that trigger the onset of puberty , ovulatory cycle and menstruation . So , we want to be very careful about leaping to conclusions about what these trends mean , but the trends themselves are very , very apparent .
These are ongoing collections of data , but just to give you a sense to how the data are falling out in a couple of different countries just to give you a a flavor . But for those of you listening and for those of you watching , the essence of all of these findings is that puberty is happening much , much earlier with each passing decade . So for instance , in the United States , around 1900 or 1903 , the average age of men or the onset of puberty in females was about 14 years old .
