Deficiency in Vitamin D, an in vogue immunomodulator, has been shown in emerging data to have a substantial pathogenetic role in allergic related diseases, particularly asthma. The concept of a shared upper and lower airway has allowed the natural extrapolation of its role in contributing to allergic rhinitis (AR). Various studies have reported the linkage with conflicting results, potentially owing to the complexity of Vitamin D biochemistry within our immune system. This systematic review and meta-analysis aims to examine the relationship between Vitamin D levels and allergic rhinitis in the paediatric population. From the 19 studies streamlined from the body of literature (up to April 2015), the authors presented two main findings.
First, both the incidence and prevalence of AR have no significant relationships with Vitamin D levels. Second, the mean Vitamin D levels in children with AR were found lower than that in controls, although such association was not observed within the adult population.
From the latter finding, the authors suggested a few explanations and proposed that AR is more likely to cause Vitamin D deficiency rather than a reverse causal relationship. This is due to parents being more likely to restrict children with AR from outdoor exposure which will subsequently lead to reduced sun exposure and Vitamin D synthesis. Also, the co-existence of other allergic diseases, such as asthma and atopic dermatitis, are more likely to require steroids treatment which can similarly impair Vitamin D metabolism. To this end, it does not appear that the lack of sunshine, which is not uncommon in the UK, can be blamed for AR. Furthermore, in its conclusion, the authors did not find sufficient evidence to support Vitamin D supplementation in the prevention of AR in children.