Vitamin D in asthma and allergy: what next?

M uch of the original work on vitamin D and asthma incidence focused on birth cohort studies. These studies examined the effect of maternal intake of vitamin D during pregnancy and its impact on asthma/wheeze in the first few years of life [1–3]. In all three of these methodologically wellperformed birth cohort studies, higher maternal intake of vitamin D was associated with a lower incidence of asthma and wheeze in the child. However, one cohort study with very a small sample size and high loss to follow-up may have obtained spurious negative results as a consequence of these significant methodological flaws [4]. Another relevant concern is that the positive studies did not measure vitamin D directly but simply looked at maternal vitamin D intake, mostly from supplements, as a proxy for vitamin D levels.