Vitamin D supplementation during pregnancy may have no preventive effect against childhood wheezing when started too late, suggests a new UK study.
In the randomized controlled trial, 180 pregnant (Asian, Middle Eastern, African American, or Caucasian) women at 27 weeks gestation received either 800 IU vitamin D daily until delivery, a single oral dose of 200,000 IU vitamin D or no treatment (1). Three years after birth, cases of childhood wheezing, respiratory allergic reactions and infections were documented and compared. The study results showed that supplemen-tation did improve, but did not optimize, vitamin D status: median umbilical cord vitamin D levels at delivery were significantly lower in women without vitamin D treatment (7 ng/ml) compared to the daily dose group (10.5 ng/ml) and the large one time dose group (10 ng/ml). No difference in the occurrence of wheezing, prevalence of eczema (skin irritation), allergies, or lung function between the three groups was found.
The researchers commented that supplementation with vitamin D may have started too late (at 27 weeks of gestation) to show beneficial effects for the children’s respiratory health. It is known that immune cells deve-lop much earlier in fetal life, and that airway development to the respiratory bronchioles is complete by
16 weeks of gestation. It may be that supplementation earlier in pregnancy, or indeed pre-conception, is necessary for protection against childhood wheezing, they said.
Several observational studies have suggested a protective effect of higher maternal vitamin D intake during pregnancy against the risk of wheezing (2), asthma and allergic rhinitis (3) and eczema (4) in offspring. The active metabolite of vitamin D, 1,25 dihydroxyvitamin D, has been shown in animal and in vitro models to have potent immune effects and a role in early lung development (5). It has been proposed that prenatal vitamin D supplementation may prevent childhood wheezing and asthma (6). The current recommended intake for pregnant women is 400 IU/day in the UK and 600 IU in the US. It has been shown that a daily dose of 4000 IU of vitamin D is safe and effective for the short term treatment of vitamin D deficiency
during pregnancy (7). Nevertheless, vitamin D insufficiency is very common during pregnancy.