My nine-year-old daughter has just started her period. She has consistently been tall for her age, and began developing breasts at age seven. I know that it is unusual to begin menstruating at this age, but is it abnormal? Will it alter her growth pattern? Are my friends accurate when they say it could be caused by too much bovine growth hormone in the fast foods she eats? And how do I help her cope with this? She is mentally and emotionally still very much a nine year old.

There is crucial information your daughter needs to know.

First, some background: The age of onset of puberty varies widely. In girls, the breast bud is usually the first sign, and is seen on average at 10-11 years. Pubic hair usually begins to appear 6-12 months later. Next comes the pubertal growth spurt. Lastly, menstruation begins (called menarche), on average, 2-2.5 years after the onset of puberty. The mean age for a girl's first period is 12.75 years. Wide variations are seen in the sequence and timing of these events, but peak growth velocity (fastest growth rate) always precedes menarche.

For boys, the testes and scrotum begin to enlarge first, usually at about 10 to 13 years. A few months later, pubic hair develops (facial hair comes about 2 years later). The pubertal growth spurt usually follows about 6 months after pubic hair. Lastly, the penis grows longer about 1 year after the testes grow, and is accompanied by changes in the voice.

Precocious puberty is defined as the onset of true puberty before 7 to 8 years of age in girls or 9 years of age in boys. (Isolated breast development which doesn't progress to the rest of puberty is called premature thelarche, and is a different, benign condition). Precocious puberty is 10 times more common in girls than in boys. Sexual development may begin at any age. Pregnancy has been reported as early as 5 1/2 years old.

Most precocious puberty is simply early maturation. Nevertheless, the Lawson Wilkins Pediatric Endocrine Society recommends evaluating for an underlying medical condition in Caucasian-American girls who have development of breast and/or pubic hair before age seven and in African-American girls before age six (Kaplowitz and Oberfield, Pediatrics 1999 Oct;104(4 Pt 1):936-41). These medical conditions include ovarian cysts, thyroid problems, McCune-Albright syndrome, central nervous system disorders, or external sources of estrogen. In girls over age 6, these other causes are quite rare, but should at least be considered by your pediatrician.

Your friends have suggested that bovine growth hormone is the cause of your daughter's precocious puberty. I strongly doubt that. The only external compounds clearly implicated in girls' early puberty are estrogens. Moreover, when human growth hormone is intentionally given to children to increase their heights, in doses far higher than your daughter could accidentally consume, precocious puberty has not been a problem. Your friends are right to be concerned about the chemicals used by agribusiness, but from bovine growth hormone I would be more concerned about cancer.

Early maturation in girls is categorized in two main types: rapidly progressive and slowly progressive. Most girls who begin puberty early (especially those who begin before age 6) have the rapidly progressive variety. They go through each of the stages (including closure of the growth plates of the bones) at a very rapid pace, and thus lose much of their adult height potential. About 1/3 of these girls will end up shorter than the 5th percentile of adult height. Many girls, however (particularly those beginning puberty after their 7th birthdays), will start puberty early, but still go through each of the stages at a more typical pace.