Last month, in The Developing Story, we discussed research findings confirming that girls in the US and in other developed countries are starting puberty at younger ages than in generations past. Although many people confuse girls’ pubertal onset with first menstrual period (or menarche), menstruation occurs relatively late in the long process. When we talk about beginning puberty, we’re primarily referring to the first signs of breast and pubic hair development, which can take place years before a girl’s first period.

As we outlined last month, some of the main suspected culprits of early puberty include obesity, environmental chemicals (that mimic hormones in the body), and psychosocial stress (including low socioeconomic status). This month, we unpack the first of these culprits: carrying extra weight.

The “obesity epidemic” in the US has received a good deal of attention in the media. Children are heavier now than in any other time in history. We know that being overweight is related to a number of poor health outcomes in childhood (metabolic syndrome, fatty liver) and in adulthood (diabetes, cardiovascular disease). As a result, some researchers have projected that this generation of children, on average, may be the first to have shorter life spans than their parents. A lesser known effect of excess weight is the link to early puberty. It has long been established that girls who are heavier tend to get their periods at younger ages. But more recently research has uncovered that heavier girls are also more likely to show signs of breast development at younger ages. Our colleague, Frank Biro, published two landmark studies in the journal Pediatrics, in 2010 and 2013, confirming the link between body mass index (BMI) and breast development. Using longitudinal data from our 3-site study, we examined over 1200 ethnically- and socioeconomically-diverse girls. Results showed that girls are developing earlier than in the recent past and that BMI played an important role.

It is well known that a certain amount of body fat is necessary for puberty to commence. Severe nutritional deprivation can delay puberty, as was the case among girls during the Dutch Famine in the 1940s. Delayed puberty is also seen in girls with anorexia or among those who exercise to extremes, such as gymnasts or ballerinas. This makes sense from an evolutionary perspective. The body requires a certain level of body fat to trigger reproductive development and to successfully support an eventual pregnancy. We now know, however, that body composition can also have an effect in the other direction -- higher body fat prompts significantly earlier puberty in girls.

Why would a girl’s extra weight influence her timing of puberty when that seems far less logical from an evolutionary perspective? The answer is in the biology. Long thought to be a dormant tissue, we now know that body fat is actually quite active. Fat in the body secretes estrogen, the hormone that is responsible for gonadal development, which includes the development of breast tissue. Typically, we would expect estrogen in the body to arise exclusively from the gonadal axis, originating in the pituitary gland, which is responsible for prompting puberty. However, given the active role of body fat in producing estrogen, we now know that it serves as another source of extra estrogen within the girl’s body.

The combination of being overweight and starting puberty early can have profound social and psychological implications for girls. Both have been linked to issues with self-esteem and poor body image. These psychological consequences have also been linked to mental health problems, such as anxiety and depressive symptoms.

On a positive note, body weight is one of the few modifiable targets for intervention to prevent early puberty, and it’s one that we have some control over in our society. As you can imagine, being overweight as a youngster puts one at risk for being overweight as an adolescent and later as an adult. Preventive measures will need to start early. These include healthful food choices and adequate physical activity. Interventions will require not just family and community support but they will demand changes at the policy level as well. With high fat foods and sweetened beverages being marketed forcefully and constantly, we’ll need to find structural ways to change the exposures that kids and families face while improving access to healthful food.

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