Purpose of review: A link between vitamin D supplementation and allergy was already suspected soon after it became possible to chemically synthesise vitamin D2 by means of ultraviolet radiation. During the past decade, the assumed allergenic effect was confirmed by clinical and epidemiological studies although the most recent discussion has centred more on vitamin D insufficiency. The purpose of this review is to summarise studies published during the past year while attempting to reconcile some apparent inconsistencies.
Recent findings: Two new concepts are presented here – epigenetic programming of the fetal vitamin D system by low maternal vitamin D supply (Barker's paradox) and ubiquitous vitamin D exposure of the newborn (Rose's paradox). Taken together a misdirected epigenetic programming offers an explanation why also vitamin D insufficiency in pregnancy may be associated with increased allergy rates in the offspring.
At least eight studies examined the association of early 25-hydroxy-vitamin D levels and atopic diseases in 2011, whereas no new study addressed the question of vitamin D supplementation in the newborn period. One study tested the whole range of 25-hydroxy-vitamin D levels in cord blood describing a U-shaped association with 2.4-fold odds ratio of low and 4-fold odds ratio of high levels to develop allergen-specific immunoglobulin E.
Summary: Randomised clinical trials with vitamin D supplements are therefore highly required. Several key points are presented for designing vitamin D trials.