Table 1.
Comparison of children in two birth cohorts, grouped according to genotype (rs174575) and breastfeeding, on tested intelligence (IQ) and covariates
| Samples and measures | rs174575 CC homozygotes |
rs174575 CG heterozygotes |
rs174575 GG homozygotes |
|||
|---|---|---|---|---|---|---|
| Not breastfed | Breastfed | Not breastfed | Breastfed | Not breastfed | Breastfed | |
| New Zealand (Dunedin) birth cohort | n = 183 | n = 238 | n = 153 | n = 201 | n = 35 | n = 48 |
| Children's IQ | 98.4 (15.2) | 103.2 (13.9) | 95.8 (12.4) | 104.0 (13.4) | 100.3 (11.2) | 98.9 (13.8) |
| Socioeconomic status (1 = low; 3 = high)* | 1.9 (0.60) | 2.0 (0.65) | 1.8 (0.55) | 2.1 (0.60) | 1.9 (0.53) | 1.9 (0.58) |
| Maternal cognitive ability† | 97.1 (15.2) | 102.4 (15.2) | 96.0 (12.9) | 103.6 (14.2) | 100.2 (13.4) | 103.3 (14.9) |
| Gestational age,‡ weeks | 40.0 (1.7) | 40.0 (1.5) | 39.7 (2.0) | 40.2 (1.5) | 39.9 (1.7) | 40.2 (1.6) |
| Birthweight,§ g | 3,399 (535) | 3,374 (491) | 3,289 (609) | 3,467 (462) | 3,431 (450) | 3,344 (347) |
| British (E-risk study) birth cohort | n = 524 | n = 488 | n = 375 | n = 337 | n = 61 | n = 63 |
| Children's IQ | 97.3 (14.1) | 104.0 (15.0) | 97.2 (13.9) | 104.6 (15.3) | 99.9 (15.3) | 100.7 (17.3) |
| Socioeconomic status (1 = low; 3 = high)* | 1.7 (0.75) | 2.3 (0.79) | 1.7 (0.76) | 2.3 (0.75) | 1.9 (0.77) | 2.4 (0.68) |
| Maternal cognitive ability† | 95.1 (14.9) | 105.0 (12.9) | 98.5 (12.7) | 105.2 (13.8) | 91.8 (14.5) | 102.6 (14.4) |
| Gestational age,‡ weeks | 36.4 (2.6) | 36.1 (2.9) | 36.4 (2.2) | 36.2 (3.1) | 36.5 (2.8) | 36.0 (3.6) |
| Birthweight,§ g | 2,452 (517) | 2,404 (572) | 2,442 (485) | 2,466 (550) | 2,490 (462) | 2,483 (690) |
Entries in the table are means and standard deviations. IQ scores were standardized to M = 100 and SD = 15 in each cohort.
*In both the Dunedin and E-risk cohorts, genotype was not associated with social class (P = 0.34 and 0.23), breastfeeding was significantly associated with social class (P < 0.001), and there was no difference in the association between breastfeeding and social class by genotype (P = 0.93 and 0.77).
†In the Dunedin cohort, maternal cognitive ability was assessed with the SRA verbal test (56). In the E-risk cohort, mothers were administered the Wide Range Achievement Test (57). Scores were standardized to M = 100 and SD = 15. In both the Dunedin and E-risk cohorts, genotype was not associated with maternal IQ (P = 0.39 and 0.84), breastfeeding was significantly associated with maternal IQ (P < 0.001), and there was no difference in the association between breastfeeding and maternal IQ by genotype (P = 0.85 and 0.34).
‡In both the Dunedin and E-risk cohorts, genotype was not associated with gestational age (P = 0.81 and 0.78), breastfeeding was associated with gestational age in Dunedin (P = 0.04) but not in E-risk (P = 0.11), and there was no difference in the association between breastfeeding and gestational age by genotype (P = 0.13 and 0.99).
§In both the Dunedin and E-risk cohorts, genotype was not associated with birth weight (P = 0.99 and 0.32), breastfeeding was not associated with birth weight (P = 0.13 and 0.61), and there was no difference in the association between breastfeeding and birth weight by genotype (P = 0.27 and 0.39).