Association between breastfeeding and lung function measurements by maternal asthma, fully adjusted model with interaction
| Lung function (unit) | Mothers without asthma | Mothers with asthma | |
|---|---|---|---|
| estimate (CI) | estimate (CI) | p-interaction | |
| FVC* (L) | |||
| No BF (mean) | 3.44 (3.18 to 3.70) | 3.35 (3.01 to 3.69) | |
| BF ≤3 months (% difference) | 2.38 (– 6.37 to 11.13) | 8.54 (– 5.68 to 22.75) | 0.471 |
| BF >3 months (% difference) | 3.09 (– 4.93 to 11.10) | 6.59 (– 7.92 to 21.09) | 0.689 |
| FEV1* (L) | |||
| No BF (mean) | 2.97 (2.73 to 3.20) | 2.90 (2.59 to 3.21) | |
| BF ≤3 months (% difference) | 5.27 (– 4.18 to 14.71) | 3.80 (– 10.48 to 18.07) | 0.869 |
| BF >3 months (% difference) | 3.23 (– 5.19 to 11.65) | 12.88 (– 3.25 to 29.01) | 0.308 |
| FEF50* (L/s) | |||
| No BF (mean) | 3.54 (2.97 to 4.12) | 3.40 (2.66 to 4.14) | |
| BF ≤3 months (% difference) | 11.10 (– 9.47 to 31.66) | 1.15 (– 27.30 to 29.61) | 0.591 |
| BF >3 months (% difference) | 4.20 (– 13.21 to 21.60) | 31.27 (– 7.11 to 69.65) | 0.198 |
| FRC* (L) | |||
| No BF (mean) | 1.99 (1.79 to 2.20) | 1.98 (1.71 to 2.26) | |
| BF ≤3 months (% difference) | 1.87 (– 9.90 to 13.64) | 9.90 (– 9.60 to 29.40) | 0.490 |
| BF >3 months (% difference) | 2.45 (– 8.35 to 13.24) | 15.20 (– 6.01 to 36.40) | 0.299 |
| RV* (L) | |||
| No BF (mean) | 1.12 (0.97 to 1.26) | 1.08 (0.89 to 1.27) | |
| BF ≤3 months (% difference) | −4.98 (– 19.15 to 9.18) | 6.67 (– 17.75 to 31.10) | 0.414 |
| BF >3 months (% difference) | 4.73 (– 9.51 to 18.97) | 31.65 (0.36 to 62.93) | 0.117 |
| TLC* (L) | |||
| No BF (mean) | 4.44 (4.17 to 4.72) | 4.38 (4.02 to 4.75) | |
| BF ≤3 months (% difference) | 2.07 (– 5.08 to 9.23) | 9.32 (– 2.45 to 21.08) | 0.303 |
| BF >3 months (% difference) | 4.65 (– 2.04 to 11.34) | 11.36 (– 1.08 to 23.80) | 0.365 |
| ADC* (cm2/s) | |||
| No BF (mean) | 0.09 (0.08 to 0.10) | 0.09 (0.08 to 0.10) | |
| BF ≤3 months (% difference) | |||
| absolute ADC value | 1.41 (– 6.87 to 9.70) | −4.00 (– 16.12 to 8.13) | 0.437 |
| average alveolar size† | 3.41 (– 15.82 to 24.98) | 1.69 (– 12.52 to 17.17) | |
| BF >3 months (% difference) | |||
| absolute ADC value | −0.47 (– 7.89 to 6.96) | 11.04 (– 3.61 to 25.70) | 0.174 |
| average alveolar size† | −1.20 (– 17.98 to 17.70) | 28.58 (– 8.45 to 73.50) |
In this model we adjusted for age, sex, height, preterm status, birth weight, Townsend score, smoking during pregnancy, maternal asthma, maternal ethnicity, and early-onset wheeze (wheezing history with onset during the first year of life) and included an interaction term between breastfeeding and maternal asthma. The means and coefficients for the groups of children of mother with and without asthma were calculated using the regression coefficients for breastfeeding, maternal asthma and the interaction term, using the command lincom in Stata, which computes point estimates, CIs and p-values for linear combinations of coefficients.
*All analyses were performed using the natural logarithm; the estimates were back-transformed from the logarithmic scale to the original scale, therefore the coefficients are multiplicative (they represent ratios; eg, in children of mothers without asthma, participants breastfed ≤3 months had an ADC value 1.4% higher than participants who were not breastfed)
†The average alveolar size was calculated with the formula ADC ratio=(volume ratio)0.415, see Narayanan et al.13
ADC, apparent diffusion coefficient; BF, breastfeeding; FEF50, forced mid-expiratory flow; FEV1, forced expiratory volume at 1 second; FRC, functional residual capacity; FVC, forced vital capacity; p-int, p-interaction; RV, residual volume; TLC, total lung capacity.