This past week, I conducted a physical examination on a nine-year-old girl with clear breast development. The mother was alarmed. She was concerned about a hormone abnormality and asked me whether there was something in her daughter’s diet that was producing this change.
Among her other concerns, she didn’t want early sexual development to turn her daughter into one of the “fast girls” who struggles with her reputation.
The truth is that sexual development in 9-year-olds is becoming increasingly common, because the average age of puberty is falling in girls in many countries, including the United States.
Textbooks say that puberty in girls may start anywhere from 8 to 13 years of age, while puberty in boys follows by about two years. Genetics account for around 50% of the variation. This is likely to explain some of the observed racial differences. In the United States, about 25% of African American girls and 15% of Hispanic girls versus 5% of White girls having at least some pubertal development by age 8.
Puberty is a prolonged process that occurs in a number of stages. For girls, enlargement of breast tissue usually precedes growth of pubic and axillary hair and the beginning of the menstrual cycle begins. Even after menstruation, the process continues with a deepening of the voice, increased growth of body on the legs and arms, and acceleration of growth velocity from about 2 inches yearly to up to 5 inches. The process culminates when the growth plates fuse and adult height is achieved.
For boys the onset of puberty is recognized with the beginning of testicular enlargement, but, again, sexual development occurs in several stages over a prolonged period. For both boys and girls, there can be variations in the order of the changes and the speed of the progression. For example, some girls develop a small amount of pubic hair several months or years before other sexual development begins. Boys can develop a small amount of breast tissue at a relatively young age. Although these types of developments can be embarrassing, they are common, and they are not a cause for alarm.
There are likely to be numerous reasons for the progressively younger ages at which puberty is beginning in girls. The average age has fallen from about 16 years of age in the 19th century to 13 years in the 20th century. Boys do not seem to be affected to the same degree, but the trajectory towards younger ages of puberty in girls is continuing. In a recent study, 10% of Caucasian girls were now starting puberty at 7 years of age.
While better nutrition is one of the theories to explain the reduction in the age of puberty from the 19th to the 20th centuries, the further on-going progression may be due to increasing body fat.
As girls become overweight, the excess fat is associated with increased estrogen and an earlier start for puberty. Conversely, a low body weight from athletic participation or from low nutritional intake, can delay puberty. The association between increased body weight and puberty is not limited to the pre-pubertal period but excess weight early in life can also mediate subsequent hormonal changes. In addition to body weight, diets low in dietary fiber and high in protein may also accelerate puberty independent of body weight.
Environmental factors are strongly suspected of increasing risk of early puberty. The influence of BST in milk on age of puberty, although not definitively proven, is one of the reasons that use of this hormone has been restricted in Canada. This restriction did not appear to alter the relative age at sexual development. Other environmental exposures, such as PCBs (polychlorinatedbiphenyl) can act like estrogen and may influence hormonal changes.
The same is suspected of bisphenol A (BPA) a chemical that is used in certain hard plastics like baby bottles and water
bottles, that is now being evaluated by regulatory authorities.
However, there may also be important social influences. One of the most intriguing is known as the Vandenbergh Effect, which defines an observed phenomenon in which young girls who have significant interactions with adult males show signs of sexual development at an earlier age relative to young girl without such an interaction. The mechanism of this effect is unknown, but it suggests that physiological processes can be influenced by situational triggers.
So, what are the adverse effects of early puberty?
The problem with earlier sexual development is that it poses challenges for those girls who are out of sync with their peers. Young girls with more sexual development than her friends are likely to feel uncomfortable. A sense of isolation may lead to depression. Studies show that girls who mature earlier are more likely to have poor body image and engage in riskier behavior. Another important consequence of early puberty is decreased adult height. Children who start early may end early and have fewer years to grow. Girls who start puberty earlier are also at a statistically increased risk of breast or uterine cancer.
The falling median age of puberty may be an environmental issue, but there are steps to be taken to prevent premature puberty relative to peers, which is the source of concern for both children and parents. Early puberty is one more reason to avoid excess weight, which is an epidemic problem in the United States. It is also another reason to consider a balanced diet with appropriate quantities of fiber and low amounts of fat. Regular checkups are important because the physician can chart growth and development of sexual characteristics with the potential of intervening when development is proceeding in front of norms. Early sexual development is rarely a sign of a significant underlying medical problem, but it can be.
Although mothers need not be alarmed by a 9-year-old with modest breast development, the pace of sexual development should not be ignored.