Health supplements for allergic rhinitis: A mixed-methods systematic review

Allergic rhinitis is a chronic inflammatory condition caused by an exaggerated response of the immune system to common allergens. Most pharmacological therapies tend to be palliative and in some cases are associated with adverse effects. There is a growing tendency for people to self-medicate with health supplements as they are generally considered safe, however clinical studies relating to their efficacy and safety are limited. This mixed-methods systematic review aims to synthesise the available evidence relating to the treatment of allergic rhinitis with a variety of health supplements. A total of 57 062 articles were derived from searching seven online databases and evidence from 48 RCTs and 10 observational studies were reviewed for methodological quality and risk of bias. No qualitative studies meeting the inclusion criteria could be found, therefore only a quantitative review was performed. Promising evidence for the following single supplements were found: apple polyphenols, tomato extract, spirulina, chlorophyll c2, honey, conjugated linoleic acid, MSM, isoquercitrin, vitamins C, D and E, as well as probiotics. Combination formulas may also be beneficial, particularly specific probiotic complexes, a mixture of vitamin D₃, quercetin and Perilla frutescens, as well as the combination of vitamin D₃ and L. reuteri. Owing to the paucity of good quality evidence, recommendations pertaining to the use of health supplements for allergic rhinitis should involve a shared decision-making process between the healthcare provider and the patient, taking into account their efficacy, safety and cost. Further good quality clinical studies and qualitative research would further our understanding of the role these health supplements may play in future treatment protocols.