The average age at baseline was 8.28 years (±1.68) (). Approximately 57 percent of the sample was female. African American children were younger (p <.05) and had slightly more total fat mass than European American children. Neighborhood composite index scores ranged between −1.94 and 5.68 standard deviation units below and above the mean. Percentages for the individual items of the composite neighborhood disadvantage score are also provided, African American children were significantly more likely to live in disordered neighborhoods (p <.05) characterized by higher unemployment, poverty, single female-headed households, and vacant housing. There were no significant racial/ethnic differences in baseline or longitudinal serum cortisol measurements.
Baseline Descriptive Statistics for Total Sample and Ethnicity. Mean (Standard Deviation)
Results from the mixed model for the full sample indicate that over the study period, pubertal stage emerged as a significant predictor of serum cortisol levels at all ages (). Post hoc analyses indicated no significant differences in the relationships between pubertal stages and serum cortisol. Fat mass was predictive of lower serum cortisol among children. The second model included the individual level covariates and neighborhood disorder. Over the study period, neighborhood disadvantage predicted lower serum cortisol levels such that children who lived in disordered neighborhoods had lower serum cortisol levels than children in more socially ordered areas. In this model, the most significant predictor of serum cortisol levels was pubertal stage 2 where, at this stage of puberty, reduced serum cortisol levels were evident. With the inclusion of neighborhood effects in the model, pubertal stages 2 and 3 became significant and both negatively affected serum cortisol levels. Post hoc analyses indicated that children in pubertal stage 2 had significantly lower serum cortisol levels than children in pubertal stage 4 (p<.05).
Mixed Model for Longitudinal Trends in Serum Cortisol Levels among a Biethnic Cohort of Children
reports longitudinal results for African American children. In the first model, none of the independent variables were significant predictors of total serum cortisol. When the neighborhood disadvantage measure was included, pubertal stage 3, nested in age, was significantly predictive of lower serum cortisol levels p <.05. The composite neighborhood disorder index was also predictive of lower serum cortisol levels (p<.05), such that over time, neighborhood stressors affected cortisol and resulted in lower serum cortisol levels.
Mixed Model for Longitudinal Trends in Serum Cortisol Levels among African American Children
provides results for the European American children. As children progressed through the pubertal transition, significant effects on serum cortisol emerged. Pubertal stages 1, 2, and 3 nested in age, significantly predicted serum cortisol such that, at each pubertal stage, children had lower serum cortisol levels. Children entering pubertal stage 2 had significantly lower serum cortisol levels relative to pubertal stages three and four (p <.05). The neighborhood composite index was marginally significant (p <.10) and predicted increased serum cortisol levels. In this model, all pubertal stages retained significance, and children in pubertal stage 2 had significantly lower serum cortisol relative to children in pubertal stage 4 (p <.05). Post hoc analyses indicated that there were no significant differences in the neighborhood disorder regression coefficient across racial/ethnic groups (p>.05).
Mixed Model for Longitudinal Trends in Serum Cortisol Levels among European American Children
Separate mixed models by gender were also conducted. While both models showed that neighborhood index operated negatively on serum cortisol, neither indicated significant relationships between neighborhood disorder and serum cortisol (data not presented).