Sunlight exposure and the risk of allergic conditions in children Original paper

In this cohort study, increased sunlight exposure during pregnancy was associated with a lower risk of asthma at age 8–9. However, some methodological issues reduce our confidence in the results.

The association between sunlight exposure and allergic conditions.

2,260 children (51% boys, 49% girls) born in 5 maternity hospitals in Paris, France.

In this cohort study, the participants were assessed for how much sunlight their mothers received during pregnancy and how much they received during the first year of life, and these data were subsequently analyzed for associations with allergies.

Allergies were measured by (i) measuring allergic sensitization via levels of immunoglobulin E (IgE) antibodies on 1 test at 18 months and 3 different tests at 8–9 years of age and (ii) the risk of having symptoms of asthma, hay fever, or eczema at 8–9 years.

The researchers adjusted their analyses for the following potential confounders: date of birth, sex of the child, birth weight, parental history of allergy, maternal smoking, moving during pregnancy, other siblings, geographic origin of parents, place of residence, family socioeconomic status, exclusive breastfeeding, day care, exposure to smoking, repeated lower respiratory tract infections, and traffic-related air pollution during the first year of life.

Increased sunlight exposure during pregnancy was associated with reduced asthma rates in children 8–9.

In addition, increased sunlight exposure during pregnancy and the first year of life was associated with lowered allergy sensitization rates in 1 of 3 tests in children at 8–9.

It is unclear exactly how the researchers assessed sunlight exposure, but it appears to largely reflect seasonality, rather than geography, because the researchers adjusted their analyses for the place of residence. Sunlight exposure strengths varied by more than a factor of 2 amongst the participants (690 Joules per centimeter squared vs 1,650 Joules per centimeter squared), suggesting that these differences were due to mothers being pregnant during different times of year.

In addition to there being less light in the winter, at Paris latitude, there would not be enough ultraviolet B radiation to produce vitamin D during much of the winter. This study would have benefited from the researchers directly measuring vitamin D levels in mothers and/or the offspring, instead of relying on the proxy of sunlight exposure.

Furthermore, only half of the participants (1,080) in this study were retained at age 8–9, due to many families having moved away from Paris.