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Early Life Exposures and Pubertal Trajectories among Mexican American Boys and Girls

Sat, March 23, 8:00 to 9:30am, Baltimore Convention Center, Floor: Level 3, Room 328

Integrative Statement

Introduction
Early puberty is linked to poor outcomes for girls and boys (see Mendle et al, 2007, 2012 for reviews). Girls’ puberty is starting earlier in the U.S. (Euling et al, 2008), and boys may be experiencing earlier puberty based on certain markers (Hermann-Giddens et al., 2012). There are ethnic disparities in pubertal timing, with Mexican-origin youth starting earlier than European Americans. Little is known about whether early life factors, including socioeconomic status and early life stress, are associated with pubertal timing and contribute to these ethnic differences. Moreover, scarce research has examined the tempo at which youth progress through puberty. Finally, almost no research has focused specifically on Mexican-origin youth or considered ethnic-specific stressors such as discrimination.

Methods
We used longitudinal data from a cohort study of 611 Mexican American adolescents living in a farmworker community in California. Tanner staging was conducted to assess breast and pubic hair development (females) and genital and pubic hair development (males). Seven assessments were conducted from ages 9y to 14y. Logistic growth mixed effects models were used to obtain individual estimates of timing (average age at which participants were halfway through puberty, Tanner Stage 3) and tempo (rate of puberty) for boys and girls separately. We then examined interindividual differences in pubertal timing and tempo as a function of family income-to-poverty ratio, father absence, household density, depressive symptoms, and standardized BMI (each assessed at 9y).

Results
Most girls initiated puberty (entered stage 2) by 9.75y for breast development and 10.5y for pubic hair, whereas most boys initiated puberty by 11.25y for genital development and 12y for pubic hair (Table 1). Logistic growth mixed effects models (Table 2) showed that boys, on average, entered Tanner Stage 3 at 13.16y for genital development and 13.16y for pubic hair development, progressing at a rate of 0.91 and 1.23 Tanner stages per year, respectively. Girls, on average, entered Stage 3 at 12.02y for breast development and 12.81y for pubic hair development, progressing at 0.66 and 0.73 stages per year. Timing and tempo were positively associated across secondary sex characteristics with the exception of genital development for boys. Finally, higher BMI was associated with earlier timing and tempo of girls’ breast (βtming = -0.16, SE = 0.05, t = -3.25, p < .01; βtempo = -0.02, SE = 0.01, t = -3.36, p < .05) and pubic hair development (βtiming = -0.17, SE = 0.05, t = -3.73, p < .001; βtempo = -0.05, SE = 0.01, t = -3.69, p < .001), controlling for family income-to-poverty ratio, father absence, household density, and depressive symptoms at 9 years of age. These other adversity factors were not associated with girls’ timing or tempo, nor were any associations significant for boys.

Conclusion: Consistent with previous work, higher BMI was associated with girl’s earlier puberty. Data analyses are underway examining additional adversity variables, including life events, acculturation, discrimination, and fear/worry about deportation. We are also conducting further analyses examining age at pubertal onset (transition from Tanner Stage 1 to 2).

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