Obesity has been associated with a specific non-allergic asthma phenotype and to a deficiency of vitamin D in at least 90% of the pediatric population. Adolescents with non-allergic asthma and vitamin D deficiency have up to six times the risk [OR: 6.2 (IC95% 2.0-21.6), p=0.002] of having a severe asthmatic crisis and do not respond adequately to inhaled steroid treatment.

To evaluate the effect of oral vitamin D3 supplementation with 50,000 IU single dose and 4,000 IU daily vs 2,000 IU daily on the Asthma Control Questionnaire score, number and incidence of asthmatic crisis, lung function, and Th17 inflammatory biomarkers in adolescents with asthma associated to obesity and vitamin D insufficiency/deficiency for three months.

Randomized controlled, double-blind, parallel (2 arms), clinical trial. Eligibility criteria: adolescents (12-17 years old), with obesity, vitamin D deficiency (<30 ng/dl), controlled or partially controlled or uncontrolled asthma according to GINA 2020 criteria and confirmed with a spirometry, with negative allergy skin test.

To each patient it will be performed a medical history, physical examination, asthma control questionnaire, a spirometry (with bronchodilator), as well as a peripheral blood sample collection of 10 ml to measure Th17 inflammatory biomarkers by chemiluminescence immunoassay and quantitative polymerase chain reaction (genetic expression of 18 cytokines) and 25-hydroxyvitamin D plasmatic concentration with electrochemiluminescence.

Patients will be randomized by block and assigned to one of two intervention arms. Each intervention arm will have a total sample of 132 patients. Experimental group will receive a single dose of 50,000 IU and 4,000 IU of vitamin D daily for 3 months. On the other hand, the active control group will receive 2,000 IU daily for 3 months. Patients will be followed up and cited every month for clinical assessment, asthma control (ACQ) questionnaire application, spirometry (with bronchodilator) and peripheral blood sample collection to determine the plasma concentration of 25-hydroxyvitamin D and Th17 inflammatory biomarkers.

Inclusion Criteria:

• Adolescents of 12 to 17 years old.
• Diagnosis of exogen obesity with a body mass index (BMI) greater than percentile 95 for age and sex, according to the Center for Disease Control and Prevention (CDC) graphics, that precedes the diagnosis of asthma.
• Plasmatic concentration of 25-hydroxyvitamin D less than 30 ng/ml at screening visit based on local laboratory test.
• Physician-diagnosed asthma, with more than 6 months of evolution, based on medical history, physical examination, clinical criteria according to the Global Initiative For Asthma 2020 (GINA) and confirmed with a spirometry with reversibility after the administration of a bronchodilator.
• Asthma severity (intermittent or mild persistent or moderate persistent) according to the National Asthma Education and Prevention Program (NAEPP) and classified as controlled, partly controlled or uncontrolled according to GINA 2020.
• Negative allergic skin tests.

Exclusion Criteria:

• History of systemic or chronic degenerative disease (renal, pulmonar, cardiovascular, infectious, muscular, immunological, hypertension, diabetes mellitus, cancer, nonalcoholic fatty liver disease).
• Current treatment with immunomodulators or immunostimulants, up to 6 months before the intervention.
• History of adverse effects to vitamin D.
• Treatment with oral steroids 3 months previous to the enrollment.
• Active smoking.

Elimination criteria:

• Parents, tutors, legal guardians or participants that decide to withdraw from the study any time.
• Pregnancy during study.
• Severe adverse effects to vitamin D.

The masking will be done by a care provider. Each patient will have a randomly assigned envelope with the corresponding vitamin D dose, defining the allocated arm.