Girls in Denmark are now entering puberty more than a year
earlier than they were 15 years ago.
Although there is a naturally wide range in the age that
healthy girls enter puberty, a new study finds the age may
be shifting younger for the entire population.
The shift toward a younger age is of concern because it exposes
girls to hormones for more of their life and may lead to damaging
Earlier puberty is associated with increased risk of breast
cancer, ovarian cancer and polycystic ovarian syndrome later
in life. Girls experiencing early puberty may also be more
likely to exhibit delinquent behaviors, substance abuse and
Possible explanations for this shift are that hormonally
active chemicals in our homes and environment are leading
to earlier sexual development in children.
Several studies in the U.S. have suggested that breast development
in girls has been occurring earlier. However, these studies
were comparing their results to the results of separate studies
performed in the past and using different measurement methods.
In girls, the beginning of breast development signifies the
onset of puberty.
Researchers in this study examined more than 1,000 school
girls in Copenhagen in 1991-1993. They then recruited and
examined almost 1,000 more girls in 2006-2008 using the same
methods. When the earlier group was compared with the later
group, the results confirm that the age of breast development
is, indeed, earlier.
Average age at first breast development was 10.9 years old
in 1991-1993 but was 9.9 years old in 2006-2008. Age at first
menstruation and age at first pubic hair development were
also younger in 2006-2008, but only by 0.2-0.3 years.
Overall, the effect of earlier breast development was much
stronger than other stages of puberty. Although puberty often
occurs earlier in overweight girls, this finding persisted
even when the authors took weight into account.