Several years ago, I started a thread asking for input on the possible reasons for the fact that the average age of menarche (the onset of mensis) had dropped steadily in the last century, to the point that a daughter often starts getting her period a full year earlier than her mother did.
I speculated that it might be our more sedentary lifestyle, seeing as how very active girls, such as gymnasts, hit puberty later than their peers.
Others said it was due to better nutrition and the amount of body fat, although there was second-hand input from a health professional that since body fat varies greatly from girl to girl, there ought to be more observed difference in the age of onset.
Well, I can only speak to what I’ve observed, and the only prepubescent girls I spend any time with are my nieces. I was just visiting yesterday, and my almost-nine-year-old niece was wearing a snug shirt … I’d swear it looks like she’s just starting to develop. Her mother, my younger sister, was almost eleven when she started, if I remember correctly. My niece is as thin as a rail, and extremely active.
This fits the “30 years ago” thing, as my sister is 39.
Well, if your niece is just now developing breast buds around nine, their menarche will be about two years from then (periods mark the end of puberty). Which isn’t early at all (that’s when I started).
I have a niece who’s thirteen and she’s chubby, although now losing a lot of her girth as she gets taller. Her mother started her period when she was 10. Niece hasn’t started yet.
I have heard that the magic trigger for menarche is when a girl hit 100 lbs. I did a Google on this and found lots of pages making the claim but no good cites (menarche start “100 pounds”).
My own 9 year old is at about 98 lbs and has started showing signs of breast development so we are a little worried about how soon it may come. (As an aside, she isn’t over-weight it’s just that she is nearly 5 feet tall :eek:. How many 9 year old girls are taller than their grandmother?)
From what I can find it is this weight trigger that is the surest indicator. This is also why childhood obesity is a problem with early onset. The sooner they get to that magic number the sooner it starts.
[Pediatrician mode]Onset of breast development is not associated with absolute weight, 100 pounds or otherwise, and has indeed moved up over the past 40 years by half to a full year. Black girls have onset about half to one year earlier than white girls and the association of earlier onset with obesity is not found in Black girls. Onset of periods (menarche) has moved slightly earlier in both populations and is earlier in Black girls than in White girls. There is a correlation of these trends with increased obeisty, and as that linked Pediatrics article notes, with early signs of obesity. Such an association suggests causation but such may end up not being the case. Others have speculated that environmental pollutants (pesticides, insecticides, etc.) with weak but synergistic estrogenic (female sex hormone) effects, may be responsible for this earlier onset of breast development without significant change in menarche. Variable sensitivity to the effects of such exposures would not be inconsistent with the findings in the linked article. Anecdotally I also see lots more normal variant male breast development that I used to. In short, the obesity link to onset of puberty without significantly effected the achievement of pubertal completion is suggestive but hardly established.[/Pediatrician mode]
Sorry for being obtuse. To try again: we know that breast development is starting earlier but that puberty is ending nearly the same time as before. We do not know why. The speculation that obesity is the cause is still just that: speculation.
Just to further complicate the issue there is also a link between onset of puberty and the presence of a father figure. Girls growing up in households without a constant strong male presence enter puberty significantly earlier.
It has been proposed that this is a normal human reproductive tactic. Under conditions where males don’t invest time in raising children there is no advantage in gaining emotional maturity before becoming pregnant since the only viable partner selction criterion is genes. Since any girl can select good genes based on appearance without any degree of emotional maturity the optimal reproductive strategy becomes “the earlier the better”. That is further reinforced because without a present father the optimal way of ensuring male protection/assistance is to become sexually active. Hence absent father: earlier puberty.
Of course while the link is established the reasons are purely speculative. However this would explain why puberty is occuring earlier, it would also explain why blacks have seen a greater decline in age of puberty than whites. Unfortunately any analysis suffers from the interplay of all these factors. Obesity is more prevalent in low income families, as are fmailies with no father figure. As a result we might be looking at two related factors or just a single factor with two indicators.
I was doing great right up until the last sentence.