Maternal vitamin D status modifies the effects of early life tobacco exposure on child lung function

Prior studies suggest that vitamin D may modify the effects of environmental exposures; however, none have investigated gestational vitamin D and cumulative tobacco smoke exposure (TSE) throughout pregnancy and early life.

This study investigated the effects of early life TSE on child lung function and the modulatory effects of gestational vitamin D on this association.

The VDAART (Vitamin D Antenatal Asthma Reduction Trial) recruited nonsmoking pregnant women and followed the mother-child pairs to age 6 years. TSE was assessed with questionnaires and plasma cotinine measurements in the mothers (10-18 and 32-38 gestational weeks) and children (1, 3, and 6 years). Cumulative TSE was calculated from the repeated cotinine measurements. 25-hydroxyvitamin D (25[OH]D) levels were measured at 10-18 and 32-38 gestational weeks. Lung function was assessed at 6 years with spirometry and impulse oscillometry.

Of the 476 mother-child pairs, 205 (43%) had increased cotinine levels at ≥1 time point. Cumulative TSE was associated with decreased FEV₁ (β = -0.043 L, P = .018) and increased respiratory resistance at 5 Hz (R5; β = 0.060 kPa/L/s, P = .002). This association persisted in subjects with insufficient (<30 ng/mL) 25(OH)D levels throughout pregnancy (β = 0.077 kPa/L/s, P = .016 for R5) but not among those with sufficient levels throughout pregnancy.

Cumulative TSE from pregnancy to childhood is associated with dose- and duration-dependent decreases in child lung function at 6 years even in the absence of reported maternal smoking. Gestational vitamin D may modulate this effect and have therapeutic potential for minimizing the adverse effect of TSE on lung throughout early life.

Maternal Vitamin D Supplementation to Prevent Childhood Asthma (VDAART); clinicaltrials.gov identifier: NCT00920621.