Observational studies have suggested that low levels of vitamin D might increase the risk of asthma, atopic dermatitis and raised immunoglobulin E (IgE) levels. However, randomised trials have provided inconclusive results.
In a study in PLoS Medicine
(online, 9 May 2017), researchers used a method that minimises the risk of bias owing to confounding and reverse causation, called Mendelian randomisation, to study the effect of four genetic variants associated with vitamin D levels.
The team found there was no significant association between any of the variants and the risk of asthma (n=146,761), childhood-onset asthma (n=15,008), atopic dermatitis (n=40,835) or elevated IgE levels (n=12,853).
They say the results indicate that the previously reported associations between vitamin D and atopic disease were most likely to be due to confounding and that vitamin D supplementation is therefore unlikely to decrease rates of these conditions.
 Manousaki D, Paternoster L, Standl M et al. Vitamin D levels and susceptibility to asthma, elevated immunoglobulin E levels, and atopic dermatitis: a Mendelian randomization study. PLoS Med 14(5): e1002294. doi: 10.1371/journal.pmed.1002294