Abstract 609

In adults, there is a strong relationship between body size and hypertension. Blacks and women of both races have a higher prevalence of hypertension. Tracking has been reported for systolic blood pressure (SBP) and body mass index (BMI) during adolescence. In a longitudinal study, we examined whether the relationship between BMI and level of SBP during adolescence was stronger in blacks than whites and in girls than boys. SBP and BMI were collected from 507 twin pairs from the MCV Cardiovascular Twin Study, measured repeatedly at 11, 12.5, 14 and 15.5 years. Using one twin selected at random, we fitted linear models using Mx to test for causal pathways. Significant effects of race and sex on the variability of SBP and BMI were found. Table 1 shows the proportion of variance of SBP at age 15.5 associated with four sources. Race and sex differences may occur from new effects(n), effects common to all ages(c), from SBP(p) and BMI(b) at previous ages (see Figure 1). The importance of these effects differs among the four groups. Correlations between SBP and BMI are significant only in white girls and boys. The SBP-BMI correlation at age 15.5 can be explained by the initial correlation at age 11 and by direct causal paths from BMI to SBP (b). Paths from SBP to BMI were not significant. The best explanation of the relationship between SBP and BMI is a common determinant - possibly a gene for growth - that influences body size and vascular growth at 11 or earlier and persists to influence these variables throughout adolescence in whites.

Table 1 No caption available.
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Figure 1
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