Table 3.
Associations Between BMI/FMI and FT3 and FT4 Levels at Age 7 as Tested Both by Conventional Epidemiological Approaches and Through the Application of Instrumental Variable Analysis Using a 32-SNP Weighted Allelic BMI Score as an Instrument
| Adiposity | Model | n | Observational Linear Regression |
Instrumental Variable Regression (Weighted Allelic Score With 32 SNPs) |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| B (95% CI) | β-(std) (95% CI) | P Value | F-Statistic | Partial R2 | B (95% CI) | β-(std) (95% CI) | P Value | P Value (DWH) | |||
| FT3 age 7 | |||||||||||
| BMI (kg/m2) | Model 1 | 3014 | 0.05 (0.04, 0.06) | 0.13 (0.10, 0.16) | 5.30 × 10−16 | 72.4 | 0.009 | 0.22 (0.07, 0.36) | 0.35 (0.11, 0.58) | .004 | .08 |
| Age 7 | Model 2 | 3014 | 0.05 (0.04, 0.06) | 0.16 (0.13, 0.19) | 6.61 × 10−21 | 73.7 | 0.009 | 0.22 (0.08, 0.36) | 0.35 (0.143 0.57) | .002 | .09 |
| Model 3a | 2538 | 0.04 (0.03, 0.05) | 0.12 (0.08, 0.16) | 4.02 × 10−13 | 56.6 | 0.08 | 0.24 (0.06, 0.42) | 0.38 (0.09, 0.68) | .01 | .06 | |
| FMI (kg/m2) | Model 1 | 3014 | 0.22 (0.17, 0.26) | 0.17 (0.13 0.20) | 1.56 × 10−22 | 100.4 | 0.03 | 0.19 (0.07, 0.31) | 0.30 (0.10, 0.50) | .002 | .21 |
| Age 9 | Model 2 | 3014 | 0.23 (0.19, 0.27) | 0.19 (0.16, 0.23) | 2.16 × 10−27 | 100.7 | 0.11 | 0.19 (0.08, 0.31) | 0.31 (0.12, 0.50) | .001 | .22 |
| Model 3a | 2538 | 0.17 (0.12, 0.22) | 0.13 (0.09, 0.17) | 3.99 × 10−12 | 79.5 | 0.09 | 0.20 (0.05, 0.35) | 0.32 (0.08, 0.56) | .008 | .14 | |
| FT4 age 7 | |||||||||||
| BMI (kg/m2) | Model 1 | 3014 | −0.07 (−0.10, −0.03) | −0.05 (−0.08, −0.02) | .001 | 72.4 | 0.01 | 0.01 (−0.37, 0.40) | 0.01 (−0.23, 0.24) | .96 | .58 |
| Age 7 | Model 2 | 3014 | −0.12 (−0.16, −0.08) | −0.10 (−0.13, −0.06) | 1.64 × 10−08 | 67.6 | 0.11 | −0.18 (−0.56, 0.20) | −0.11 (−0.34, 0.12) | .35 | .92 |
| Model 3a | 2538 | −0.09 (−0.14, −0.05) | −0.08 (−0.12, −0.04) | .00003 | 46.8 | 0.10 | −0.11 (−0.58, 0.38) | −0.06 (−0.36, 0.23) | .68 | .92 | |
| FMI (kg/m2) | Model 1 | 3014 | −0.01 (−0.02, −0.001) | −0.04 (−0.07, −0.002) | .04 | 100 | 0.02 | −0.01 (−0.33, 0.32) | −0.004 (−0.21, 0.20) | .97 | .81 |
| Age 9 | Model 2 | 3014 | −0.03 (−0.04, −0.02) | −0.09 (−0.13, −0.06) | 2.42 × 10−07 | 90.3 | 0.11 | −0.18 (−0.51, 0.14) | −0.11 (−0.32, 0.09) | .28 | .76 |
| Model 3a | 2538 | −0.02 (−0.03, −0.01) | −0.07 (−0.11, −0.03) | .002 | 74.1 | 0.11 | −0.07 (−0.47, 0.34) | −0.04 (−0.28, 0.21) | .75 | .76 | |
Model 1 adjusted for age and sex model 2 adjusted for model 1 and other thyroid hormone parameters. Model 3 adjusted for model 2 and height, markers of social class, and early life environment (home ownership, maternal age at birth of child, maternal highest educational qualification, maternal smoking in pregnancy, family adversity index, and parents and home score). B, β-coefficient; P, strength of evidence against the null hypothesis of no association; P (DWH), P value of the Durbin form of the DWH test, which examines the difference between the estimates from linear regression and instrumental variable analysis.
A total of 476 individuals with missing data.