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MANY girls in the us are starting pubertyfar earlier than is widely considerednormal, according to a recently published report of the first large-scale,multi-racial study conducted by MarciaE Herman-Giddens, professor of maternal and child health at the Chapel HillSchool of Public Health, University ofNorth Carolina. Nearly half of theAfrican -Arnerican and 15 per cent ofCaucasians girls studied, reached pubertyand began developing sexually by theage of eight (Paediatrics, Vol 99, No 4).
This study involved over 17,000 girlsin the age-group of three to 12 years,who were seen in 65 paediatric clinics allover the us. About 1,600 of the girls, or9.6 per cent, were African-American. Atthe age of eight years, 48.3 per cent ofthe African-American girls and 14.7 percent of the Caucasian girls began developing breasts or pubic hair or both.Menstruation started at 12.16 years inthe African -American girls on an average and at 12.88 years for Caucasiangirls. The average age of menstruationhas remained almost unchanged for over 45 years.
This study challenges the textbooktimetable of puberty, based on decadesold research on British girls. Existingmedical guidelines have it that it isabnormal for girls to show the firstsigns of puberty before the age ofeight. As this study shows that a largepercentage of American girls haveone or both of these characteristics at seven years of age, and insome cases by three years, eitherthe textbooks are outmoded orthere are some other, unknownfactors. The early onset ofpuberty was noticed in boththe Caucasian and the African-American girls, although thereracial differences.were someOn an average, the AfricanAmerican girls showed thefirst signs of sexual maturityabout a year earlier than theCaucasian girls.
To understand the implications of these observations, it isimportant to elaborate on therole of the hormone oestrogen inthe human body, particularly inearly puberty. Oestrogen is apowerful chemical with itsreceptors in about 300 differenthuman tissues from the brain tobone to the liver. Its levels beginto rise at the age of about eight.The hypothalamus plays animportant part as it spurs thepituitary gland to release hormones, which in turn promptthe ovaries to produce oestrogen. By the age of 11 or 12 years.production of oestrogen andother hormones begins to trigger thedevelopment of breasts, growth of theunderarm and pubic hair, and thebeginning of menstruation.
In addition, these hormones alsotrigger adolescent features such as oilierhair and blemished skin. In fact oestrogen starts its functions in the pre-natalstate. It helps in the formation of thefoetus's brain during its early stages ofdevelopment. It also affects learningability and memory through later life.Scientists are not very clear as to howoestrogen works in the brain, but its roleclearly goes beyond menstruation.
Herman-Giddens and her teamwanted to find out whether 'environmental oestrogens', chemicals thatmimic oestrogen, are bringing about theearly puberty noticed in the Americangirls. Such a relationship between environmental contamination and sexualabnormality, was noticed in the early80s by scientists working on alligators.While studying as to how many alligators from Florida's Lake Apopka couldbe hunted without making the population crash, it was noticed that many ofthe males had become nearly sterile.Subsequent research showed that thousands of gallons Of DDT-containing pesticide was responsible. This started thestudy of gender-bending characteristics of pesticides.
Subsequently it was also confirmedthat hundreds of chemicals of the postwar age resemble the human sex hormone oestrogen. These include polychlorinated biphenyles, used in themanufacture of electronics, pesticidessuch as endosulfan and atrazine, polycarbonate plastic found in many babybottles and water jugs and chlorinecompounds that bleach paper. Theirmolecular structure resembles that ofoestrogen, so they influence the samereceptors in the body that are sensitiveto oestrogen, as the receptors cannotdistinguish them. Consequently, the,oestrogen mimics' can trick the bodyinto turning off, or boosting certain bio-chemical pathways, especially in thereproductive system, disturbing normaldevelopment in both sexes.
Though the role of oestrogenlike pollutants in diseases like breastcancer and emdometriosis, the painfulinflammation of the uterine lining thatoften causes infertility, has been investigated, there are still no confirmed studies to show that the pollutants canactually switch on the same biologicalpathways as real oestrogen. Abnormalities in males due to oestrogen mimics, including testicular malformationsat birth, have been reported in severalcountries.