Exposure to sunlight and allergic morbidity in children (Pollution and Asthma Risk: an Infant Study)

BACKGROUND: Sunlight relationship with allergies is poorly studied in children. Thus, we examined how early exposure to solar radiation is associated with allergic morbidity in the PARIS birth cohort. METHODS: This study dealt with children who attended at least one of the two health check-ups: 18 months (n = 2012) and 8/9 years (n = 1080). Early exposure (prenatal and during the first year of life) to solar radiation was assessed using meteorological data (solar radiation, temperature, relative humidity). Children with similar exposure trajectories were grouped by longitudinal and multidimensional cluster analysis. Association of solar radiation exposure with allergic morbidity (i.e. allergic sensitisation at 18 months and 8/9 y., current asthma, rhinitis, and eczema at 8/9 y.) was quantified by multivariable logistic regression models adjusted for potential confounders. The effect modification of maternal vitamin D (VitD) supplementation during pregnancy was also tested. RESULTS: Four exposure trajectories were found. The trajectory with the highest exposure to early solar radiation had a reduced risk of sensitisation at 8/9 y. compared to the trajectory with the lowest exposure (p = 0.06). This association was statistically significant in the VitD supplemented subgroup. Solar radiation during pre- and post-natal period was significantly associated with a lower risk of sensitisation at 8/9 y. (for ↗IQR, aOR: 0.47; 95%CI: 0.25-0.87 and 0.84;0.70-1.00, respectively). Increased prenatal exposure to solar radiation was significantly associated with a lower asthma risk at 8/9 y. (for ↗IQR, 0.32; 0.10-0.96). CONCLUSIONS: Early sunlight exposure may reduce the risk of sensitisation and asthma in school-aged children, especially in those prenatally exposed to VitD intake. These findings highlight the importance of VitD in preventing allergic diseases in children, either through supplementation or sunlight exposure. KEY MESSAGES: • Pre-natal and early postnatal exposure to sunlight could reduce the risk of sensitisation and asthma among school-aged children. • The association may be explained by vitamin D immunomodulatory effect, highlighting its importance in preventing allergic diseases in children through supplementation or sunlight exposure.