Interpreting the continued decline in the average age at menarche: results from two nationally representative surveys of U.S. girls studied 10 years apart.
OBJECTIVE
To determine whether average age at menarche declined in the United States during the past decade, and whether associations between menarcheal timing, weight status, and race/ethnicity changed.


METHODS
Relative weight, race/ethnicity, and menarcheal status of girls (n = 1577) in the National Health and Nutrition Examination Survey (NHANES) III (1988-1994) were compared with those of girls (n = 1720) in NHANES 1999-2002. Probit analysis estimated average age at menarche overall and also by race/ethnicity. Logistic regression assessed associations of relative weight and race/ethnicity with menarcheal status.


RESULTS
In the United States, average age at menarche declined from 12.53 years (95% confidence interval [CI] = 12.43 to 12.63 years) in 1988-1994 to 12.34 years (95% CI = 12.24 to 12.45 years) in 1999-2002. By race/ethnicity, average age at menarche estimates were as follows: non-Hispanic whites, 12.57 years (95% CI = 12.45 to 12.69 years) and 12.52 years (95% CI = 12.38 to 12.67 years); non-Hispanic blacks, 12.09 years (95% CI = 11.82 to 12.36 years) and 12.06 years (95% CI = 11.81 to 12.32 years); and Mexican Americans, 12.24 years (95% CI = 11.88 to 12.59 years) and 12.09 years (95% CI = 11.81 to 12.37 years). Higher relative weight was consistently associated with increased likelihood of having reached menarche.


CONCLUSIONS
Average age at menarche in the United States declined by 2.3 months between 1988-1994 and 1999-2002; by race/ethnicity, declines were considerably smaller. Changes in the population distribution of race/ethnicity and relative weight should be considered when interpreting trends in age at menarche.
Anderson
Sarah E
SE
Gerald J. and Dorothy R. Friedman School of Nutrition Science and Technology and the Department of Public Health and Family Medicine, Tufts University, Boston, Massachusetts 02111, USA.
Must
Aviva
A
D000293:Adolescent; D001741:Black or African American / Q000706:statistics & numerical data; D017677:Age Distribution; D015992:Body Mass Index; D002648:Child; D005260:Female; D006801:Humans; D016015:Logistic Models; D008572:Menarche / Q000208:ethnology / Q000502:physiology*; D017058:Mexican Americans / Q000706:statistics & numerical data; D014481:United States; D044465:White People / Q000706:statistics & numerical data