Parallel, randomized, placebo-controlled, and double-blind intervention trial.
75 participants (25 in each group), men and women, aged between 18 and 60 years, with moderate-severe persistent AR symptoms and dust mite allergy.
The 75 study participants will be randomly divided into three groups depending on whether they receive supplementation with the probiotic Bifidobacterium longum ES1, supplementation with the heat treated version of ES1 (HT-ES1) or placebo during the 2-month study period. After the treatment period the volunteers will be followed up for one month.
During the study, patients will be able to continue using conventional drug treatment for AR, including oral and local antihistamines, oral and intranasal corticosteroids, and intranasal decongestants.
Intervention products are the probiotic Bifidobacterium longum ES1 (ES1), the heat treated version of ES1 (HT-ES1) and a placebo (maltodextrin). The delivery format of the products to the volunteers will be in capsules.
The total duration of the study will be of 92 days (13 weeks).
Each participant will perform 4 visits. The study visits will be the following:
* a pre-selection visit to check inclusion/exclusion criteria (V0; day 1, week 1) and, in case of meeting the criteria,
* a study start visit (V1; day 8 +/-3 days; week 2),
* a final study visit (V2; day 64 +/- 3 days; week 10),
* a study follow-up visit (V3; day 92 +/- 3 days; week 14).
At visits V0, V1, V2 and V3 the use of any medications, including over the counter, will be checked.
In visits V1, V2 participants must present themselves in fasting conditions of 8 hours to obtain blood. In addition, in visits V2 and V3, participants will be asked for the presence of adverse events that could be associated with the consumption or withdrawal of the study products.
The products will be given in the V1 visit so that the participants will have all the necessary treatment to carry out the 8 weeks of study with the corresponding product.
During the study and starting from visit V0 once the volunteer has been included in the study and signed the informed consent, participants will record AR symptomatology and/or the use of AR medication on a daily basis by using the CSMS questionnaire described by Pfaar O. et al. in an online format using the Microsoft Forms application. During the study, the research team will monitor compliance of the online questionnaire by the volunteer.
Volunteers will be encouraged to maintain their dietary habits and to maintain their regular practice of physical activity during the study.
Descriptive variables related to AR and demographic variables will be obtained from participants of the study by clinical history and interviewing at visit V0.
In visits V1, V2 and V3 of the study, health-related quality of life data will be obtained by means of the Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) according to Juniper, E, et al.
For the collection of faeces in visits V1, V2 and V3, participants will be previously provided with a faeces collection kit (two different labelled tubes, one for metagenomic analysis and other for IgA determination will be provided).
