Population and study design

This work was conducted in the SCAALA Cohort (Social Change Asthma and Allergy in Latin America, Salvador, Bahia, Brazil) [51]. The study design has been described previously [52, 53]. Briefly, the original study population was composed by 1445 children, living in 24 deprived areas from the city of Salvador, Northeast Brazil, enrolled in the study to evaluate the impact of a sanitation programme on diarrhoea occurrence over the period from 1997 to 2003, when the participants were 0–3 years old [54]. The first survey on risk factors for wheezing and atopy was conducted in 2005, the second in 2007 and the third in 2013 [10, 52, 55]. The information for the present study were obtained in 2013 when data from 1206 participants were collected. At this time, the population aged 11 to 19 years old. Seven hundred and ninety-two individuals with complete data of interest were included in the current analysis. In addition, the 25(OH)D levels and specific IgE for aeroallergens (sIgE) were quantified, and vitamin D pathway genes were typed for variants. Asthma diagnosis was obtained using the International Study of Asthma and Allergy in Childhood phase III questionnaire (ISAAC PHASE III) adapted to Portuguese, answered by parents or legal guardians of each participant, or the participant himself if 18 years or older.

Ethical approval was obtained through the Ethical Committee for Health Research of the Institute of Public Health of the Federal University of Bahia, Brazil (Num. 120.616). Written informed consent was obtained from the legal guardian of each individual if they were under 18 years, and themselves if they were older than 18 years old.