[BMJ Open]Secular trends for age at spermarche among Chinese boys from 11 ethnic minorities, 1995–2010: a multiple cross-sectional study[中国11个少数民族男孩首次遗精年龄的长期趋势，1995-2010年：多重横断面研究]

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Authors
Yi Song, Jun Ma, Liu-Bai Li, Bin Dong, Zhiqiang Wang, Anette Agardh

Abstract
Objectives We compared the differences in median age at spermarche among 11 ethnic minorities in 2010, estimated the trends regarding age at spermarche in different ethnic minorities from 1995 to 2010, and explored the association of spermarche with body mass index (BMI).

Methods We used four cross-sectional Chinese National Surveys on Students’ Constitution and Health (CNSSCH, 1995, 2000, 2005 and 2010), and the total sample size was 40 113 children aged 11–18 years. The median age at spermarche of each ethnic minority was determined by using probit analysis. Logistic regression was used to assess the association of spermarche with BMI.

Results In 2010, the ethnic minorities with earliest age at spermarche were Qiang (12.03 years), Zhuang (12.91 years) and Kirghiz (13.17 years); the three ethnic minorities with latest age at spermarche were Dong (14.73 years), Yao (14.60 years), and Naxi (14.36 years). From 1995 to 2010, age at spermarche showed a decline in almost each minority group except Yao and Dong. A higher BMI was associated with an increased likelihood of having reached spermarche after adjusting for age, regions or ethnic minorities.

Conclusions A large variation in age at spermarche was observed among different ethnic minorities. The age at spermarche showed a downward shift in almost each of the 11 ethnic minorities with different patterns over time, and the children with higher BMI are more likely to enter puberty early.

BMJ Open 2016;6:e010518 doi:10.1136/bmjopen-2015-010518