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　　The multi-institutional study published in the journalPediatrics confirms that girls of all races are beginning puberty at a younger age, a longstanding observation in the US.

　　“The impact of earlier maturation in girls has important clinical implications involving psychosocial and biologic outcomes,” said Frank Biro, M.D., lead investigator.

　　“The current study suggests clinicians may need to redefine the ages for both early and late maturation in girls.”

　　Researchers have observed that girls with earlier maturation are at risk for a multitude of challenges, including lower self-esteem, higher rates of depression, norm-breaking behaviors and lower academic achievement.

　　Experts say early maturation also results in greater risks of obesity, hypertension and several cancers —including breast, ovarian and endometrial cancer.

　　The study was conducted through the Breast Cancer and Environmental Research Program, established by the National Institute of Environmental Health Science.

　　Researchers at centers in the San Francisco Bay Area, Cincinnati and New York City examined the ages of 1,239 girls at the onset of breast development and the impact of body mass index and race/ethnicity.

　　The girls ranged in age from 6 to 8 years at enrollment and were followed at regular intervals from 2004 to 2011. Researchers used well-established criteria of pubertal maturation, including the five stages of breast development known as the Tanner Breast Stages.

　　The girls were followed longitudinally, which involved multiple regular visits for each girl. Researchers said this method provided a good perspective of what happened to each girl and when it occurred.

　　Researchers found the respective ages at the onset of breast development varied by race, body mass index (obesity), and geographic location.

　　Breast development began in white, non-Hispanic girls, at a median age of 9.7 years —earlier than previously reported.

　　Black girls continue to experience breast development earlier than white girls, at a median age of 8.8 years.

　　The median age for Hispanic girls in the study was 9.3 years, and 9.7 years for Asian girls.

　　Body mass index was a stronger predictor of earlier puberty than race or ethnicity.

　　Although the research team is still working to confirm the exact environmental and physiological factors behind the phenomenon, they conclude the earlier onset of puberty in white girls is likely caused by greater obesity.

　　新的研究結果顯示，超重是女生早熟最明顯的預警因素，并且相比之前的報道，超重對白人女生早熟的影響更迅速。

　　這個由多個機構通過對美國的長期觀察得出的研究結果在美國兒科雜志上稱，各個人種的女生早熟的現(xiàn)象出現(xiàn)的越來越早。

　　首席調查員M.D.弗蘭克·比羅說：“女生的早熟現(xiàn)象對心理和物理學都有重要的臨床意義。

　　“最近的研究成果可能要求臨床醫(yī)師們重新確定女生的早熟和晚熟年齡。”

　　研究人員通過觀察發(fā)現(xiàn)早熟的女生面臨著各種各樣的挑戰(zhàn)，包括缺乏自信，更容易患抑郁癥和違反紀律，學習成績也更差。

　　專家表示早熟也會增大女生患肥胖癥、高血壓和多種癌癥的風險，包括乳腺癌、卵巢癌和子宮內膜癌。

　　這項研究由乳腺癌與環(huán)境研究項目小組實行，由國家環(huán)境衛(wèi)生科學研究所發(fā)起。

　　舊金山灣區(qū)、辛辛那提和紐約研究中心的研究人員對1239位乳房開始發(fā)育的女生進行檢查，測試身體質量指數和種族對她們的影響。

　　六歲至八歲的被測試女生從2004年到2011年每隔一段固定時間就進行檢查。研究人員采用了青春期成熟的既定標準對被測試人員進行分析，包括被稱為Tanner階段的五個乳房發(fā)育階段。

　　研究人員對這些女生進行了縱向觀察，包括對每個女生進行各種類型的定期探訪。研究人員表示這種方法能讓他們更好地了解每個女生的變化和發(fā)生變化的時間。

　　研究人員發(fā)現(xiàn)女生們乳房發(fā)育的年齡由于女生們的種族、身體質量指數（超重）和居住地不同而有所差異。

　　白色人種和非西班牙裔的女生乳房發(fā)育年齡平均為9.7歲——相比之前的報道數據要早。

　　黑色人種女生的乳房發(fā)育年齡依然比白色人種女生要早——平均為8.8歲。

　　西班牙裔的女生乳房發(fā)育平均年齡為9.3歲，亞洲女生為9.7歲。

　　身體質量指數相比人族或種族來說，是預測早熟更準確的指標。

　　雖然研究小組依然致力于找出這種現(xiàn)象背后的具體環(huán)境和生理因素，他們已經得出結論：白色人種女生的早熟有可能是肥胖導致的。