Over the last century, we have seen an increase in the standards of living and also advances in medical science and technology. We as a whole are healthier than previous generations which can mainly be attributed to a higher level of nutrition. Over the past decade, there has been a downward secular trend in the age at which young girls are experiencing puberty.

Puberty is a period of rapid skeletal and sexual maturation that occurs mainly in early adolescence. Menarche, or first menstruation, is considered the technical start of puberty. With the onset of puberty comes the maturation of secondary sexual characteristics such as the development of breasts and pubic hair. The development of secondary sexual characteristics in girls is a significant event, signaling the onset of physiological and psychological changes of profound importance to the individual. The age of onset of pubertal changes can vary with race, ethnicity, environmental conditions, geographical location, and nutrition.

In 1995, Herman-Giddens et al. launched a major study of 17,000 girls. These data suggest that girls from across the United States are developing pubertal characteristics at younger ages than currently used norms. Results indicated that the average age of menarche, or first menstruation, had fallen dramatically (from 17 to 13) between the middle of the 19th century to the middle of the 20th century. Giddens reported that the onset of secondary sexual characteristics, breast buds and pubic hair, were significantly different among white and African-American girls. Some 15% of white girls were showing outward signs of incipient sexual maturity by age 8. The results were even more startling for African-American girls. Fifteen percent were developing breasts or pubic hair by age 7, and almost 50% by age 8. Giddens also found that by age 11, 28% of African-American girls and 13% of white girls had begun menses. By age 12, 62% of African-Americans and 35% of white girls had begun menses.

Is this a peculiarly American phenomenon? Or are girls developing breasts and reaching puberty at younger ages all over the world?

A cross-sectional study of sexual maturation of normal Chinese schoolgirls in Hong Kong were performed by Huen et al. Their findings indicated a significant downard secular trend in sexual maturation. Their median age of sexual maturation are now among one of the earliest medians in the world population studied. The median age of the onset of puberty was determined to be 9.78 years, while the median age of onset of pubic hair development was 11.6 years. The median age of menarche was 12.4 years.

Across the world in a study of Brazilian women completed by Auxiliador de Santa Cruz Croel et al. found that the mean age of menarche for Brazilain women decreased from 13.7 to 12.4 years. Therefore, scientific evidence is illustrating that young girls around the world are developing earlier than previous generations.

Weight-gain

The theory that has the broadest support among scientists is that early puberty is somehow tied with weight-gain. America is in the midst of an epidemic of overweight and obese kids. According to the National Center for Health Statistics, the percentage of children ages 6 to 11 who were overweight nearly doubled, from 6.5% to 11.4%. Early breast development may be encouraged by a protein called leptin. Fat cells produce leptin. Leptin is essential for the progression of puberty.

Overweight girls tend to have more insulin circulating in their bodies. High-levels of the hormone insulin stimulates the production of sex hormones from the adrenal gland and ovary.

Hormones in the meat and milk
Some scientists feel that hormones given to cattle to make them grow bigger may linger in the food and stimulate early sexual development. There is not sufficient scientific evidence at this time to conclude whether or not steroid hormones play a key role in early maturation.

DDE

Although a vast majority favors a fat connection, other explanations do exists. One such example is chemical pollution in the food chain. DDE is a breakdown product of the pesticide DDT. Although the United States banned the use of the pesticide DDT, this breakdown product continues to persist in the environment. DDT is a plausible suspect because they mimic hormones that play a key role in the development of the reproductive system.

PCB's

PCB's were once used as flame retardants in electrical equipment. Scientists suspect that these long-lived PCB's chemicals may mimic key hormones in the reproductive system. Therefore, jump-starting sexual maturation. In a study reported in the Journal of Pediatrics, girls with high prenatal exposure to PCB's tended to hit the first stages of puberty a bit ealier than other girls.

Bisphenol A

Some researchers believe that a suite of chemicals used to make plastic may be the cause of early development. Bisphenol A is a chemical cousin of estrogen's and has been attributed to affect the reproductive systems of lab rats

There is insufficient scientific evidence at this time to conclude that DDE, PCB's, and Bisphenol A are solely responsible for the downard secular trend. Therefore, more research is neeeded to conclude whether these chemicals have any affect on sexual maturation.

Media There are a number of physicians and psychologists that blame the bombardment of sexualized messages aimed at young kids for this early developmental phenomenon. Somehow these sexualized messages trigger changes in the brain that jump-start sexual development.

What are some of the possible consequences of early sexual maturation?

Emotional and pschological stress Pressure to act more mature Harassment by boys and other girls Low self-esteem Physical dangers of sexual harassment Teen-age pregnacy Sexually transmitted diseases Loss of identity

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