The Decreasing Age Of Pubertal Onset

The data presented in the previous section on average age of breast and pubic hair development in girls and boys in the United States stem from study conducted by 225 clinicians in pediatric practices belonging to Pediatric Research in Office Settings (PROS), a practice-based research network that is part of the American Academy of Pediatrics (Herman-Giddens et al., 1997). Previous to this study, the study most often quoted as defining normative ages for puberty was the Marshall and Tanner (1969) longitudinal study of 192 White girls living in a children's home, assessed every 3 months from age 8 through age 18. Studies of pubertal onset comparable in scope to the British (Marshall and Tanner) study had not been conducted in the United States. The PROS study was cross-sectional, consisting of 17,000 girls between the ages of 3 and 12 whose breast and pubic hair development was assessed via practitioner ratings (Herman-Giddens et al., 1997). Findings from this study indicate that the mean age of pubertal onset for girls has decreased by as much as a year, compared to the Marshall and Tanner data. Furthermore, the study found that African American girls are beginning breast and pubic hair development about 6 months to a year earlier than White girls, although the reasons for the earlier age of secondary sexual characteristic onset for African American girls are not clear.

The National Health and Nutrition Examination Survey (third cycle) found similar results (Wu, Mendola, & Buck, 2002). Physician-ratings of Tanner stages of breast and pubic hair development were available for 1,623 girls between ages 8 and 16 years. Mean age of onset of pubic hair and breast development was 9.5 and 9.5 years for African American girls, 10.3 and 9.8 years for Mexican American girls, and 10.5 and 10.3 years for White girls. These ethnic differences remained even after adjustment for current body mass index and several social and economic variables (Wu et al., 2002).

Changes in the age of menarche in the United States across the past few decades are not as clear. In a large study of puberty in girls conducted between 1966 and 1970, the U.S. National Health Examination Survey, assessed age of menarche in girls between the ages of12 and 17 (Harlan, Harlan, & Grillo, 1980). Data from this study indicated that age of menarche was 12.8 years for White girls and 12.5 years for African American girls. The age of menarche for White girls in the PROS study, 12.88 years, was similar to the 1980 report, whereas the age for African American girls in the PROS study, 12.16 years, was slightly lower (Herman-Giddens et al., 1997). A study based in Chicago neighborhoods in the mid- to late 1990s, which included African American, White, and Latina girls from low-, middle-, and high-socioeconomic status reported younger ages of menarche than the previously mentioned studies (Obeidallah, Brennan, Brooks-Gunn, Kindlon, & Earls, 2000). Results showed that Latina girls reached menarche at a younger age (11.58 years) than African American girls (11.93 years), after controlling for socioeconomic factors. Adjusting for socioeconomic status, no significant differences were found between White girls (12.04 years) and Latinas or between White girls and African American girls. It should be noted that not all girls in this study had begun to menstruate, so the means are lower than they ultimately will be, although the ethnic differences should hold.

Although findings for boys indicate that there may be variations in puberty onset by race (Sun et al., 2002), no clear data indicate that boys are entering puberty earlier now than they were twenty or thirty years ago. Implications for potential effects of earlier pubertal timing on depression in girls will be reviewed later in the chapter.

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