Associations among insulin, estrogen, and fat mass gain over the pubertal transition in African-American and European-American girls.
BACKGROUND
Age at menarche (AgeM) is earlier in African-American (AA) than in European-American (EA) girls. Neither the physiological cause nor the health implications of this difference are known.


OBJECTIVE
We tested the hypotheses that higher insulin among AA vs. EA precipitates an earlier elevation of estradiol (E2), an associated earlier AgeM, and greater gain in body fat.


METHODS
The study was conducted at a university research laboratory and General Clinical Research Center.


METHODS
Subjects were 137 girls (57 AA and 80 EA) aged 7-15 yr.


METHODS
The study had a longitudinal design. Annual evaluations were conducted for body composition by dual-energy X-ray absorptiometry, acute insulin response to glucose (AIRg) by iv glucose tolerance test, and reproductive-endocrine profile.


METHODS
Multiple linear regression modeling and mixed model analyses were used to identify independent predictors of AgeM and E2 concentration at menarche.


RESULTS
AgeM was significantly earlier in AA vs. EA (10.8 vs. 11.6 yr). Neither E2 nor insulin was a significant independent predictor of AgeM. AIRg was a significant predictor of E2 concentration. AA had higher E2 than EA (P < 0.01), and girls with higher AIRg had higher E2. Total fat increased with age in both EA and AA. However, among EA, the increase in fat mass was similar both before and after menarche (9.4%/yr before vs. 10.0%/yr after), whereas among AA, fat deposition nearly doubled after menarche (8.4%/yr before vs. 14.9%/yr after).


CONCLUSIONS
Results did not support a direct cause-and-effect relationship between higher insulin, higher E2, and earlier AgeM in AA girls. However, the data suggested that higher insulin was associated with higher E2. Furthermore, reproductive maturation appeared to be associated with an acceleration of fat deposition among AA girls.
Casazza
Krista
K
Department of Nutrition Sciences, University of Alabama at Birmingham, 1530 3rd Avenue South, Birmingham, AL 35294-3360, USA. kristac@uab.edu
Goran
Michael I
MI
Gower
Barbara A
BA
D000273:Adipose Tissue / Q000378:metabolism*; D000293:Adolescent; D001741:Black or African American; D001823:Body Composition; D002648:Child; D004958:Estradiol / Q000097:blood*; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood*; D008137:Longitudinal Studies; D008572:Menarche; D044465:White People
D007328:Insulin; D004958:Estradiol