Sun Exposure and Asthma Prevalence in Spanish Schoolchildren and Adolescents in the Global Asthma Network (GAN) Phase I Study: A Semi-Individual Cross-Sectional Study

Background/Objective: In the multifactorial etiology of asthma, environmental factors, including sun exposure, measured either by sunshine hours (SHs) or global solar surface irradiance (GSSI), are critical. The objective of this study is to estimate the association between sun exposure and the prevalence of asthma in Spanish schoolchildren (6–7 years old) and adolescents (13–14 years old) from six geographic centers in Spain (A Coruña, Bilbao, Cantabria, Cartagena, Pamplona and Salamanca) included in the Global Asthma Network (GAN) study during 2016–2019. Methods: Measurements of SHs and GSSI were obtained from the Spanish “Agencia Estatal de Meteorología”. A semi-individual cross-sectional design was used, and multilevel logistic regression models were employed, with adjustments for age, sex, temperature, relative humidity and gross domestic product, taking the center as the reference level. Permutation tests were performed to account for the low number of centers. Results: Increases in both SHs and GSSI were associated with a lower prevalence of “asthma ever” in the 6–7 and 13–14 years age groups. An increase of 100 annual sunshine hours was associated with a lower prevalence of “asthma ever” among schoolchildren (adjusted odds ratio [aOR] = 0.82; 95% confidence interval [CI], 0.79–0.85); from the crude model, permutation p = 0.08. In adolescents, the corresponding estimates were aOR = 0.90 (95% CI, 0.87–0.94); from the crude model, permutation p = 0.02. An increase of 1 kWh m−2 day−1 in GSSI was associated with a lower prevalence of “asthma ever” among schoolchildren (aOR = 0.15; 95% CI, 0.10–0.23); from the crude model, permutation p = 0.25. In adolescents, the corresponding estimates were aOR = 0.37 (95% CI, 0.25–0.54); from the crude model, permutation p = 0.01. Conclusions: The results of this study suggest that sun exposure, measured either as SHs or GSSI, may be protective against asthma in adolescents. In contrast, the association between sun exposure and the prevalence of “asthma ever” in schoolchildren was not significant, although it followed a similar trend. Confirmation of these findings in other geographical settings could improve our understanding of the role of sun exposure in asthma prevention and control.