Are children today really going through puberty earlier?
1977年， 在意大利米兰附近一所学校，许多幼小的男女学生突然出现了胸部发育的症状。据后来发表在LANCET 上的调查报告称，受污染的牛肉及家禽可能是这次事件的元凶。10年前，在加利弗里亚也发生了一宗类似事件，有7个孩子表现出了青春期的症状，而起因源于一种用于治疗结核病的药不小心掺入了一些类似于雌激素的混合物。笔者曾经在2006年的NEW YORK TIMES 上发表的一篇报道中进述过这样一件事情：一家两兄妹在未达到上幼儿园的年龄之前就出开始长出阴毛。究其原因，原来是孩子的父亲为了美容和提高性生活质量，偷偷使用了一种从网上药店买来的强效的睾丸激素霜; 小孩在与大人的日常接触中，也受到了影响。
In 1977, hundreds of young Italian boys and girls attending a school near Milan suddenly began growing breasts. A subsequent investigation published in the Lancet suggested that contaminated beef and poultry were the likely cause. A decade earlier, another outbreak of early puberty in seven young kids in California had been traced to a tuberculosis drug that was accidently laced with estrogen-like compounds. In a 2006 piece for the New York Times—which, incidentally, was embellished for an episode of House—I described the case of a brother and sister who began growing pubic hair before reaching kindergarten. It turned out their father was secretly applying a high-potency testosterone cream purchased from an Internet pharmacy, for supposed cosmetic and sexual performance benefits, and the cream was rubbing off onto his kids from normal daily contact.
As with infections or chemical spills, early puberty can occur in small outbreaks. But can it also happen on a larger, population-wide scale? Recently, a drumbeat of scientific publications have speculated that children today undergo puberty earlier than in decades past, spurring worry about pervasive environmental triggers like bisphenol-A (BPA), phthalates, and obesity.
But a closer look at the data suggests that fears about early puberty may be misplaced.
The concerns about widespread early puberty began in the 1990s, when a North Carolina physician's assistant named Marcia Herman-Giddens wondered why many 7- and 8-year old girls appeared to be developing breasts. She organized a study in which 225 pediatricians graded the maturity of young girls' breasts and pubic areas. In a controversial 1997 Pediatrics paper, she concluded that puberty occurred earlier than in previously reported federal health studies from the 1960s.
去年，丹麦的研究者对比了两组有关性早熟特征的数据（一组收集于2006至2008年间，另一组从1991到1993年）后，也发现女孩子青春期的出现比以前早了一年。本月早些时候，一只由 Frank Biro 带领的辛辛那提市儿童医院的研究团队在一篇报告中说，从2004到2006年，被查检出有性早熟特征的美国女孩的青春期甚至比 Herman-Giddens 所报告的时间更早出现。从而也加剧了人们对早熟趋势的担忧。
Last year, Danish researchers compared data taken from girls from 2006 to 2008 to another cohort from 1991 to 1993 and also found the breast and pubic hair development was now occurring earlier by about one year. And in a well-publicized study released earlier this month, a team led by Frank Biro of Cincinnati Children's Hospital reported that American girls examined between 2004 and 2006 appeared to undergo puberty even earlier than reported by Herman-Giddens, prompting fears that the trend was accelerating.
Is it really possible that the process of human maturation could be changing rapidly? Identifying the start of puberty is very subjective and many studies showing earlier puberty, particularly those that focus on breast development, can be flawed and misleading. The key is to find a more reliable marker of puberty.
Thankfully, there is one.
The precise trigger for sexual maturation is unknown, but sometime during childhood, a grape-sized area of the brain called the hypothalamus decides one night that it's time to grow up. Beginning that night, the hypothalamus periodically drops a bit of a hormone called GnRH just onto the pea-sized pituitary gland, rousing it from its lifelong slumber.
The pituitary then secretes its own hormones into the circulation, ultimately activating the adrenal glands and ovaries (which make lots of estrogen) or testes (which make lots of testosterone). In girls, the first sign of puberty is typically a slight budding of the breast; in boys, it's a mild enlargement of the testicles. Over the next years, other changes arrive: pubic and underarm hair, voice deepening, the adolescent growth spurt, acne, menstruation or semen production, and so on.
With no objective blood test or scan, most experts consider breast budding and testicular growth the hallmarks of puberty's beginning. Unfortunately, those measures are very subjective—particularly for male children. Pediatricians guess the size of a boy's testicles by touch and comparison to a rosary-like string of balls called an orchidometer, which is not very accurate.
这就导致许多针对早熟的研究都集中在了女孩子身上——且所采用的诊断方式不也尽人意。Herman-Giddens 在1997年进行的研究中，也只是通过许多从事不同项目的儿科医生的目测， 而不是通过触摸方式来对那些具有乳房发育特征的小硬块进行系统的检查。这样就可能把胖的孩子也误诊为性早熟。
As a result, most studies of early puberty focus on girls—but those assessments aren't much better. Herman-Giddens' 1997 study relied only on visual inspection by hundreds of different pediatricians trained in different programs, and not on actually feeling systematically for the small, firm masses that typify breast buds. That might lead obese kids to be prematurely termed pubertal.
There is a much clearer and defined marker of puberty: the age of a girl's first period, or menarche. If puberty is occurring earlier, one would think menarche should also, since the process responds to the same cascade of hormones. But in the past 40 years, there hasn't been any real change in age of menarche, which remains at just over 12 years. Additionally, no researcher has shown any objective change in the timing of adolescent growth spurts. In 2008, an international group of endocrinologists and other experts led by the U.S. Environmental Protection Agency found little agreement that puberty was happening much earlier.
Perhaps researchers seeing widespread precocious puberty are just noticing breast development earlier—looking harder at normal bodies. It would follow that today's puberty would seem to take longer than in previous decades. That's precisely the case. (Epidemiologists call this "lead-time bias.")
尽管到目前为止还没有实质性的方法去证实肥胖会影响早熟，有些女孩子的早熟可能确实跟肥胖有关（但令人费解的是，肥胖的男孩子却比正常的男孩较晚进入青春期）。当然还有不得不令人担忧的就是有些毒素（如 硼化本基丙氨酸 以及 邻苯二甲酸盐）所带来的影响。
It's possible that obesity might correlate with earlier puberty in some girls (oddly, fat boys appear to have later puberty than other boys), though the population-wide effect is still imperceptible by objective measures. And there are plenty of other reasons to worry about toxins like BPA or phthalates.
But in the end, the epidemic of earlier and earlier puberty is a myth that the media love and certain researchers continue to propagate. The tale's promotion doesn't always depend on data. Instead, worries about earlier physical maturation in girls sublimate and propel concerns about society's sexualization of young girls, whether by provocative dance routines or revealing clothing. Those topics certainly get people talking. Unfortunately, any solutions are unlikely to come from the labs of our nation's endocrinologists.
2010-09-07 18:23 编辑：kuaileyingyu