New research shows obesity is the largest predictor of earlier puberty in girls, which is affecting white girls much sooner than previously reported.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。

新的研究结果显示，超重是女生早熟最明显的预警因素，并且相比之前的报道，超重对白人女生早熟的研究人员对这些女生进行了纵向观察，包括对每个女生进行各种类型的定期探访。研究人员表示这种方法能让他们更好地了解每个女生的变化和发生变化的时间。

研究人员发现女生们乳房发育的年龄由于女生们的种族、身体质量指数(超重)和居住地不同而有所差异。

白色人种和非西班牙裔的女生乳房发育年龄平均为9.7岁——相比之前的报道数据要早。

黑色人种女生的乳房发育年龄依然比白色人种女生要早——平均为8.8岁。

西班牙裔的女生乳房发育平均年龄为9.3岁，亚洲女生为9.7岁。

身体质量指数相比人族或种族来说，是预测早熟更准确的指标。

虽然研究小组依然致力于找出这种现象背后的具体环境和生理因素，他们已经得出结论：白色人种女生的早熟有可能是肥胖导致的。影响更迅速。

这个由多个机构通过对美国的长期观察得出的研究结果在美国儿科杂志上称，各个人种的女生早熟的现象出现的越来越早。

首席调查员M.D。弗兰克·比罗说：“女生的早熟现象对心理和物理学都有重要的临床意义。

“最近的研究成果可能要求临床医师们重新确定女生的早熟和晚熟年龄。”

研究人员通过观察发现早熟的女生面临着各种各样的挑战，包括缺乏自信，更容易患抑郁症和违反纪律，学习成绩也更差。

专家表示早熟也会增大女生患肥胖症、高血压和多种癌症的风险，包括乳腺癌、卵巢癌和子宫内膜癌。

这项研究由乳腺癌与环境研究项目小组实行，由国家环境卫生科学研究所发起。

旧金山湾区、辛辛那提和纽约研究中心的研究人员对1239位乳房开始发育的女生进行检查，测试身体质量指数和种族对她们的影响。

六岁至八岁的被测试女生从2004年到2011年每隔一段固定时间就进行检查。研究人员采用了青春期成熟的既定标准对被测试人员进行分析，包括被称为Tanner阶段的五个乳房发育阶段。