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Childhood Obesity Speeds the Onset of Puberty in Girls

Tuesday, April 24th, 2012

When I was young, even though my Dad wanted to “plump up” me and my sisters so that we would be less attractive to boys, for the most part, sitting down at the family table meant eating a well-balanced meal and reconnecting with each other after a busy day.  This time wasn’t just important for the bonding opportunity it provided, but for the proper nutrition it allowed my sisters and I to receive.  It was there that we learned what a balanced diet was and to appreciate the food we had.  Snacking throughout the day was a privilege and eating snacks between meals was a luxury a poor person could ill afford. Unfortunately now days, it seems that many parents don’t have time for traditional dinners or are unwilling to make time for time them.  Snacks are cheap, ubiquitous and filled with carbohydrates. With so many people reaching for the quickest, easiest foods, families are moving to a culture of convenience and their kids are paying the price.

Childhood obesity is on the rise and it’s having effects in some unexpected areas.  Studies are now suggesting that girls who are overweight start menstruation at much younger ages.  The average age of onset of menstruation (menarche) in the late 20th century was between 12.6 to 12.8 years.  Recently, that age has decreased to 12.43 years.   It has been argued that girls need to reach a critical weight (47.8 Kg) to initiate pubertal changes; it is more likely that what is needed is a shift of body composition, with an increase in the percentage of body fat. The percentage of body fat in children (16%) needs to rise to 23.5% to initiate puberty.  A 2011 study found that each 1 kg/m2 increase in childhood body-mass index (BMI) can be expected to result in a 6.5% higher absolute risk of early menarche (before age 12 years).

Normally, once a young woman reaches a particular body mass index, that tells her body she is of childbearing weight.  This starts the menstruation cycle.  If a young girl, say of about eight or nine, is overweight, she will reach this body mass index much sooner, triggering her body to go into early puberty.  While early childhood obesity is itself a problem, early puberty can also lead to a shortened growth span.  Most girls stop growing a few years after starting menstruation.  If they start this too soon, they will also stop growing much earlier than normal.  If childhood obesity continues to increase, the rise in early maturation is likely to follow.  In 1965, about 5% of kids were considered obese in the US.  Obesity in children has increased three-fold over the past 30 years.  In 1980 obesity in children, ages 6-11, was a mere 6.5% but by 2008 it increased to 19.6%.

Today, about 25 million children are either overweight or obese.  Researchers are finding that increases in the number of girls hitting puberty early seems to be in keeping with these obesity statistics.  The First Lady is even promoting a change in our habits that affect childhood obesity.

Although convenient, fattening foods have flooded the markets; there are still plenty of healthy foods out there.  Parents cannot expect their kids to make smart choices about their diets, especially at such young ages.  It’s up to them to teach their children how to eat, so they can grow up to make good choices for themselves and their own families.  There’s something to be said for those traditional sit-down dinners, because they truly benefit the health of our children in more ways than one.

— Yvonne S. Thornton, M. D., M. P. H.