Background Vitamin D is associated with lung function in adults, but its relation with childhood lung function is still unclear.

Objective To investigate whether prenatal and postnatal vitamin D supplementation and plasma level is associated with childhood lung function.

Methods In the KOALA Birth Cohort Study, children's lung function (n=436) was measured at age 6–7 years by means of spirometry and presented as forced expiratory volume in 1 s (FEV₁) z scores and forced vital capacity z scores. The mother and child's 25-hydroxyvitamin D plasma level was determined around 36 weeks of pregnancy and at age 2 years. Vitamin D supplement intake during pregnancy was defined based on the amount of vitamin D in supplements, and trimester and duration of use. Data on child's vitamin D supplement use were collected through questionnaires at ages 1, 2 and 6–7 years.

Results 25-Hydroxyvitamin D level and vitamin D supplement use in childhood were not associated with lung function. Maternal use of vitamin D at <10 μg/day (adjusted beta (AdjB −0.37; 95% CI −0.69 to −0.05)), vitamin D containing multivitamin use in the second and/or third trimester (AdjB −0.26; 95% CI −0.49 to −0.03), and use for two trimesters (AdjB −0.25; 95% CI −0.49 to −0.02) were associated with a significantly lower FEV₁ z score compared with no supplements. Maternal use of vitamin D at ≥10 μg/day and use in the first or all trimesters was not associated with significantly lower lung function levels.

Conclusion The authors found no association between 25-hydroxyvitamin D levels, vitamin D supplementation in childhood or recommended vitamin D dosage of ≥10 μg/day during pregnancy and lung function in children aged 6–7 years.