Table 4.
Linear regression models of uric acid, evaluating effect modification by VDR genotype on associations of blood and tibia lead in two groups of lead workers, dichotomized by median age (40.6 years).
| Panel 1: age < 40.6 years
|
Panel 2: age ≥ 40.6 years
|
Panel 3: age ≥ 40.6 years
|
|||||||
|---|---|---|---|---|---|---|---|---|---|
| β-Coefficient | SE β | p-Value | β-Coefficient | SE β | p-Value | β-Coefficient | SE β | p-Value | |
| Blood lead models | |||||||||
| Intercept | 4.3906 | 0.1754 | < 0.01 | 4.7529 | 0.1104 | < 0.01 | 4.6087 | 0.1074 | < 0.01 |
| Age (years) | −0.0341 | 0.0083 | < 0.01 | −0.0118 | 0.0099 | 0.23 | −0.0190 | 0.0099 | 0.06 |
| Systolic blood pressure (mm Hg) | — | — | — | — | — | — | 0.0056 | 0.0027 | 0.04 |
| Serum creatinine (mg/dL) | — | — | — | — | — | — | 2.1009 | 0.3302 | < 0.01 |
| VDR Bb or BB | 0.0073 | 0.1654 | 0.97 | −0.0447 | 0.1565 | 0.78 | −0.1201 | 0.1502 | 0.42 |
| Blood lead (μg/dL)a | −0.0056 | 0.0040 | 0.17 | 0.0111 | 0.0040 | < 0.01 | 0.0087 | 0.0038 | 0.02 |
| Blood lead × VDR Bb or BBb | 0.0018 | 0.0109 | 0.87 | −0.0041 | 0.0093 | 0.66 | −0.0026 | 0.0089 | 0.77 |
| Tibia lead models | |||||||||
| Intercept | 4.3660 | 0.1756 | < 0.01 | 4.7474 | 0.1070 | < 0.01 | 4.6267 | 0.1064 | < 0.01 |
| Age (years) | −0.0338 | 0.0083 | < 0.01 | −0.0027 | 0.0097 | 0.78 | −0.0122 | 0.0098 | 0.22 |
| Systolic blood pressure (mm Hg) | — | — | — | — | — | — | 0.0061 | 0.0027 | 0.02 |
| Serum creatinine (mg/dL) | — | — | — | — | — | — | 2.1603 | 0.4382 | < 0.01 |
| VDR Bb or BB | −0.0599 | 0.2093 | 0.78 | 0.0842 | 0.1515 | 0.58 | −0.0140 | 0.1484 | 0.93 |
| Tibia lead (μg Pb/g bone mineral)a | −0.0038 | 0.0021 | 0.07 | −0.0008 | 0.0014 | 0.57 | 0.0015 | 0.0014 | 0.27 |
| Tibia lead × VDR Bb or BBb | −0.0033 | 0.0083 | 0.69 | 0.0138 | 0.0062 | 0.03 | 0.0142 | 0.0060 | 0.02 |
| Truncated tibia lead modelsc | |||||||||
| Intercept | 4.7765 | 0.1110 | < 0.01 | 4.6361 | 0.1108 | < 0.01 | |||
| Age (years) | −0.0057 | 0.0101 | 0.57 | −0.0142 | 0.0101 | 0.16 | |||
| Systolic blood pressure (mm Hg) | — | — | — | 0.0061 | 0.0028 | 0.03 | |||
| Serum creatinine (mg/dL) | — | — | — | 2.2604 | 0.4534 | < 0.01 | |||
| VDR Bb or BB | 0.0502 | 0.1555 | 0.75 | −0.0608 | 0.1522 | 0.69 | |||
| Tibia lead (μg Pb/g bone mineral)a | 0.0036 | 0.0023 | 0.12 | 0.0026 | 0.0022 | 0.26 | |||
| Tibia lead × VDR Bb or BBb | 0.0100 | 0.0064 | 0.12 | 0.0106 | 0.0062 | 0.09 | |||
—, model shown was not adjusted for that covariate. Panels 1 and 2 display results in the younger and older groups, respectively. Panel 3 shows results in the older group after additional control for systolic blood pressure and serum creatinine. Models were also adjusted for sex, BMI, and alcohol use.
Reference category of homozygotes for the common gene allele (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 group and the regression line for the reference gene group; slopes in the variant gene group 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 VDR Bb or BB genotypes is 0.0130 in panel 2 (−0.0008 + 0.0138)].
Tibia lead levels > 103 μg Pb/g bone mineral were removed from models.