A finding across three large-scale studies conducted in the 1980s and 1990s, the PROS study (Her-man-Giddens et al., 1997), NHANES III (Wu et al., 2002), and the National Heart, Lung, and Blood Institute Growth and Health Study (Morrison et al., 1994), is that African American girls begin breast and pubic hair development about a year earlier than White girls and begin menses about half a year earlier. The reasons for the earlier age of secondary sexual characteristic onset for African American girls are not clear. Possible factors to consider include differences in diet and weight, environmental hazards or environmental estrogens, or differences in contextual stress and cultural attitudes between ethnic groups (Graber, 2003). Physiological differences that have been hypothesized to play a role in timing of pubertal onset include lower insulin sensitivity (Arslanian, Suprasongsin, & Janosky, 1997) and higher serum leptin levels (Wong et al., 1998) in African American children compared to White children. None of these hypotheses have been investigated extensively.
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