Early puberty in girls is a growing problem in the United States and around the world.

In the mid-1800s, the average age of menarche (first menstrual period) was 17. By the late 1960's it had dropped to 12, with anywhere from 9 to about 16 being considered "normal." This change can be considered positive overall; it was mostly a result of improved nutrition, which also resulted in taller stature, longer lifespans, and better overall health.

However, in recent years, the onset of puberty in girls, especially breast and pubic hair development, has dropped even lower. Among Caucasian girls in the United States, 1 in 7 has now started developing breasts and public hair by the age of 8. The figure for African-American girls is 1 in 2. Many doctors and researchers have begun to revise downward the age at which puberty is considered "precocious" - to 7 for Caucasian girls and 6 for African Americans.

But can an eight year old sporting breasts really be considered "normal?" Early onset of puberty is associated with many health risks: both physical and psychological. I believe that the medical community and parents alike must do more to learn about the causes of precocious puberty and work both to reverse the trend towards younger and younger puberty and to provide support for girls who experience it.

Environmental and genetic factors play a role in increasing or decreasing these risks for both early and late developing girls. In general, however, girls who experience precocious puberty have a higher risk of:

• Cancer. The earlier the age of first menarche, the greater a girl's risk of developing several types of cancer, particularly breast cancer, due mainly to greater lifetime exposure to the hormone estrogen.
• Menstrual and fertility problems. Increased lifetime exposure to estrogen is also associated with an increased risk of problems such as PMS, menstrual cramps, uterine fibroids, polycystic ovarian syndrome (PCOS), endometriosis, fibrocystic breasts, and more.
• Stunted growth. Early puberty is often associated with advanced skeletal age, meaning that a 6 year old girl might have the bone structure of an 8 or 9 year old. Although they might initially be taller than slower-developing girls, girls who experience precocious puberty are likely to end up shorter, because after the initial growth spurt or spurts, puberty triggers the body to stop growing up and start filling out. Slower developing girls have more time to grow tall than the average girl who experiences precocious puberty.
• Lesser brain development. Unfortunately, puberty also slows and eventually triggers the end of brain development. Again, this gives girls who experience early onset puberty less time to develop to their full physical potential before growth ceases.
• Depression, anxiety, and stress. Being different is hard on both early and late developers, and combined with the mood swings associated with puberty, many girls who experience precocious puberty also have problems coping and may need extra emotional support from parents, teachers, and other trusted adults.
• Sexual harassment. Sexual harassment of schoolchildren by other schoolchildren is a growing problem in the United States, and early developing girls are often targeted earlier and more frequently than other students, which can exacerbate depression, anxiety, and other mental problems.
• Sexual precocity. Girls with precocious puberty are often treated as sexual beings earlier than other girls and may be targeted more by older boys and even adult men than slower developing girls. They also have to deal earlier with their own sexual feelings. Girls who experience early puberty may be more likely to engage in early sexual activity, increasing their risk of teenage pregnancy or STDs.

Note to parents: because early puberty can be caused by some serious conditions, including certain types of brain tumors and thyroid diseases, it is important to consult a doctor if you are concerned about your daughter's development, especially if you have no family history of early puberty.

• Genetic factors. If a girl's mother, sisters, and other female relatives experienced early puberty, the chances are very strong she will too.
• Obesity. As the rate of childhood obesity has exploded, so has the rate of precocious puberty. This is one of the most widely accepted theories about the rise in early puberty rates. Estrogen and leptin, two important hormones in puberty, are produced by fat cells, and many researchers believe puberty in girls is triggered when the body reaches a certain percentage of fat, in combination with other factors. This is one reason many competitive youth athletes experience later puberty than their peers.
• Xenoestrogens. Xenoestrogens are man-made compounds that mimic the behavior of natural estrogen in the body. They occur in everything from plastic baby bottles and food storage containers to shampoo, cosmetics, and sunscreen to pesticides and insecticides used in residential and agricultural pest control to growth hormones fed to the animals that produce our meat, milk and eggs to the water we bathe in. Some shampoos targeted at the African-American community even advertise their estrogen content. Many scientists believe xenoestrogens are a major contributing factor to the epidemic of precocious puberty; others believe they are only minor contributors.
• Soy-based infant formula. Soy has one of the highest concentrations of phytoestrogens, which are naturally occurring plant estrogens. In adults, phytoestrogens are generally considered neutral or even beneficial, especially from dietary sources. However, some researchers feel that the concentration of phytoestrogen in soy infant formulas may reach dangerous levels because these formulas are the only or primary source of nourishment for so long. These researchers claim that infants fed soy formula receive the estrogen equivalent of five birth control pills per day (based on body weight). About 25% of infants in the United States are fed soy-based formulas.
• Sexualized television and media. In one controversial theory, some researchers claim that exposure to sexualized media may be contributing to the increase in cases of early puberty. It is clear that visual stimuli affect the brain and body chemistry. For example, a photograph of a delicious looking meal causes people to salivate. However, the degree to which media depictions of sex could affect brain and body chemistry is still extremely uncertain and highly controversial.

Here are some steps you can take to reduce the chances your daughter will experience early puberty:

Reduce exposure to xenoestrogens.

Although the involvement of xenoestrogens in early puberty remains controversial, I believe it is better to be safe than sorry. One of the most potent and notorious xenoestrogens, DDT, was originally considered to be completely safe, and remains legal in some parts of the world.

Some compounds to avoid:

• Phthalates. Plasticizers used to make plastic softer and more flexible, found in a truly depressing rangeof products, from baby bottles to IV bags to children's toys to liquid cosmetics to pesticides to food storage containers to certain clothing and footwear items. Learn more about phthalates.
  
• Bisphenol A (BPA). Another compound found in a depressing variety of plastic (and non-plastic) products, including baby bottles and tin cans, and shown to leach into food and liquids at unsafe levels, especially when heated.
• Parabens. Preservatives used in many cosmetics and toiletries. The most common include methylparaben, ethylparaben, propylparaben, and butylparaben.
• Polybrominated biphenyls (PBBs). Flame retardants, now fortunately restricted.
• DDT metabolites, especially DDE. Still found on some agricultural products.
• DEHA. A plasticizer found in some cling wrap and other soft plastics.
• BHT and BHA. Common food preservatives.
• Estradiol. Another name for estrogen. Most commonly found in shampoos marketed to African Americans, despite a proven link to early breast development.

Learn more about reducing exposure to xenoestrogens.

Breastfeed.

Breastfeeding can be frustrating, time-consuming, and even quite painful at first, but in most cases it provides the best source of nutrition for infants. The longer you breastfeed the less exposure your child will have to the phytoestrogens in soy formulas and the xenoestrogens in (non-organic) dairy formulas, as well as compounds such as phthalates and bisphenol A that occur in many baby bottles. The many other benefits of breastfeeding include lower rates of obesity and allergies in breastfed babies.

Breastfeeding may increase the risk of early puberty if the mother has been exposed to PBBs or high levels of DDT, because both can pass to the infant through breast milk.

Encourage regular moderate exercise.

Regular exercise reduces the chance of early puberty in two ways. First, it greatly reduces the chances of obesity. Second, exercise contributes to maintaining healthy hormone balance by lowering estrogen levels. (Be aware that excessive exercise can lead to too little estrogen, which also causes health problems, including increasing the risk of osteoporosis.)

Eat a balanced diet.

A balanced diet with lots of whole grains and fresh fruits and vegetables, and moderate quantities of animal products will help fight obesity and maintain healthy hormone balance as well. Eat organic foods as often as possible to reduce exposure to xenoestrogens through pesticides residues on food. The growth hormones fed to livestock are another major source of xenoestrogens. Eat organic, preferably grassfed, animal products whenever possible.

Limit Dairy Consumption

New evidence suggests that it may be best to limit milk consumption in girls at risk for early puberty, due to the combination of natural and synthetic hormones found in milk. Fermented dairy products such as yogurt and cheese are believed to be safer than plain milk, and organic milk (again, preferably grassfed) is safer than conventional milk because it does not contain synthetic growth hormones.

Monitor television and media consumption.

Although this is the most controversial possible cause of early puberty, again, better safe than sorry. Restricting age-inappropriate entertainment allows children to be children longer whether or not they are at risk of early puberty, and watching television WITH your children not only allows you to know what they're watching but also offers a prime opportunity to pass on your values through discussions about what you see onscreen and to get in some family bonding time as well. For more on smart media consumption, read Raising Smart Kids Without Throwing Out the TV.