I recently became aware that the phenomenon of precocious, or premature puberty, is much more common in children adopted internationally than in the population at large. At least according to a Danish study.

According to Kidshealth.com, these are the signs of precocious puberty:

In girls, the telltale signs of precocious puberty include any of the following before 7 or 8 years of age:

breast development
pubic or underarm hair development
rapid height growth - a growth "spurt"
onset of menstruation
acne
"mature" body odor
In boys, the signs of precocious puberty before 9 years of age include:

enlargement of the testicles or penis
pubic, underarm, or facial hair development
rapid height growth - a growth "spurt"
voice deepening
acne
"mature" body odor

The biggest problem for children who are undergoing precocious puberty is that they will undoubtedly be teased by the other children. Add that to the moodiness of puberty (too soon for the children to really deal with) and inappropriate sexual urges for their age and this can be very difficult for a child.

Here are the results from the Danish study:

In this large, nationwide, register-based study including 655 cases of precocious puberty, we found that intercountry boys and girls were 10 to 20 times more likely to develop precocious puberty compared with the Danish reference group. Older age at adoption significantly increased the risk of precocious puberty. Uncertainty of the exact age is a well-known problem in adopted children, and systematic underestimation of age might bias the result. However, using the worst-case scenario that all children who according to the Danish Civil Registration System were adopted after 2 years of age were in fact 1 year older, we still observed a highly increased risk of precocious puberty associated with adoption and especially with adoption after 2 years of age.

The researchers have several ideas as to why children adopted internationally (particularly those adopted over the age of 2) may experience precocious puberty:

An increasing number of studies have shown long-term effects of certain prenatal and postnatal growth patterns, including advancement in pubertal maturation after poor intrauterine growth and catch-up growth during childhood. Different growth patterns and dietary habits between adoptees and children immigrating with their families might contribute to explain our findings. It has been hypothesized that stressful psychosocial factors in infancy and childhood may lead to earlier pubertal maturation. In general, adoptees have experienced several traumatic life events, and it may be speculated that these events alter the susceptibility for developing precocious puberty.

Interestingly enough, the increased prevalance of precocious puberty was found in all children adopted internationally except those adopted from Korea. Since children adopted from Korea are often from a foster care setting, they typically arrive in their new families better fed and less stressed than those adopted from orphanages.