Let's talk seriously about periods.
Doctors and scientists have noticed an alarming trend. Some girls in elementary school are experiencing their first period - menarche - as early as fourth grade.
That's 9 or 10-years-old.
This shift is noticeable across the board. In the United States, the average age for a girl's first period is now just under 12-years-old. This is a year and a half earlier than the average for girls in 1900.
What does this mean? And could it be related to what they are eating?
Paediatric and Adolescent Gynaecologist Dr Julie Powell sees three potential causes for this earlier onset of girls' periods: obesity, chemical exposures and social and psychological stress.
"We know kids are more obese now than they ever were in the history of our country. Right now, about one-quarter to one-fifth of children are obese. That's not overweight, that's obese, meaning that they are significantly above their recommended body weight. Obesity in children has tripled in the last 30 years," she said.
And that may be important, she said, because fat cells make estrogen. The more fat cells you have, the more estrogen your body makes. Estrogen, of course, is the main female sex hormone (men have it too, in smaller amounts). So it makes logical sense that an overabundance of it could lead to earlier menstruation.
And the relationship between fat cells and puberty may extend beyond estrogen, Powell said. Two hormones control our appetite, she explained: ghrelin, which tells our bodies that we are hungry, and leptin, which tells us that we are full.
"There is a lot of interplay between the amount of fat cells that you make and how sensitive your body is to leptin," she said. "It looks like the fatter you are, the more insensitive you are to leptin."
And "leptin itself may be involved in puberty," she said.
The relationship between obesity and early periods has not been definitively proved, Powell said, but substantial evidence points to an association. A disproportionate number of obese girls reach puberty earlier than those of normal weight.
And while boys are also reaching puberty somewhat earlier than before (though not to the same extent as girls), obese boys tend to come to it a little later than others. One possible reason could be their increased levels of estrogen.
But as Powell pointed out, other factors may be in play besides obesity. Scientists are studying whether chemicals or hormones that we encounter every day might be having an effect. These chemicals could be naturally occurring in food or be added to them, or they may be found in everything from beauty products to furniture, she said.
Xenoestrogens are hormones that mimic the effect of estrogen or turn on estrogen receptors and act like estrogen. They can be found in certain common food preservatives, along with soy products, the plastic that lines food cans, plastic food storage containers and possibly the nonstick coating that lines pans.
Sleep deprivation, too, can lead to obesity and therefore potentially earlier periods for girls, Powell said.
"There is pretty good evidence that in children and adults that sleep is more important in hormones than we ever thought. Sleep deprivation, even for a few hours, turns on ghrelin and turns off leptin," she said.
Children from 5 to 10-years-old need 10 hours of sleep a night, "and I can guarantee you that that is a rare event now," she said.
But does any of this even matter? If girls get their periods earlier now, is that even a cause for concern?
Absolutely, said Powell, and one of the reasons she gave is absolutely chilling: "Early sexual development leads to a much higher risk of sexual abuse," she said.
So, what can we do to slow this trend?
"Try to maintain or move toward a healthy weight. Make a reasonable effort to try to avoid the accumulation of certain chemicals in our lives and in our foods" and get enough sleep, she said.
"From a dietary standpoint, we're all familiar with the recommendations for either kids or adults to get to a healthier weight: more fruits and vegetables, less sugars and processed foods."
If you can afford it, buy organic foods to avoid pesticides. If you can't buy organic, use a fruit or vegetable wash to clean certain fruits and vegetables (homemade recipes for these washes are available online, along with lists of which foods are likely to be coated with pesticides and which are not).
For more information on the subject, Powell highly recommends the book "The New Puberty," by Louise Greenspan and Julianna Deardorff. "It's a layperson's book talking about all of these issues," she said.