Table 5.
Linear regression model evaluating effect modification by combined ALAD and VDR genotypes on the association between tibia lead and uric acid, in lead workers ≥ 40.6 years of age (median).
| Blood lead models | β-Coefficient | SE β | p-Value |
|---|---|---|---|
| Intercept | 4.6078 | 0.1086 | < 0.01 |
| Age (years) | −0.0133 | 0.0099 | 0.18 |
| Systolic blood pressure (mm Hg) | 0.0058 | 0.0027 | 0.03 |
| Serum creatinine (mg/dL) | 2.1352 | 0.4420 | < 0.01 |
| ALAD1-2 and VDR bb | −0.1086 | 0.2067 | 0.60 |
| ALAD1-1 and VDR Bb or BB | 0.0111 | 0.1533 | 0.94 |
| Tibia lead (μg Pb/g bone mineral)a | −0.0008 | 0.0014 | 0.59 |
| Tibia lead × ALAD1-2 and VDR bbb | −0.0122 | 0.0079 | 0.12 |
| Tibia lead × ALAD1-1 and VDR Bb or BBb | 0.0140 | 0.0061 | 0.02 |
Models were also adjusted for sex, BMI, and alcohol use.
Reference category for homozygotes for both common gene alleles (ALAD1-1 and VDR bb).
p-Values for the cross-product terms reflect the statistical significance of the difference between the slopes of the regression line for the variant gene groups and the regression line for the reference gene group. Slopes in the variant gene groups are obtained by adding the
β-coefficient of the cross-product term to the β-coefficient for the reference category [i.e., the slope of the relation between tibia lead and uric acid in those with both the ALAD1-1 and VDR Bb or BB genotypes is 0.0132 (−0.0008 + 0.0140)].