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22 décembre 2011 4 22 /12 /décembre /2011 22:20
MedWire News : Children with an inadequate vitamin D intake are at increased risk for developing atopy, subsequent bronchial hyper-responsiveness (BHR), and asthma, show study findings.

"Vitamin D has been linked in some studies with atopy- and asthma-associated phenotypes in children with established disease, but its role in disease inception at the community level is less clear," say Patrick Holt (Telethon Institute for Child Health Research, Subiaco, Western Australia) and colleagues.

To investigate associations between vitamin D status and biologic indicators of allergy and asthma development, the team assayed serum vitamin D levels from 989 and 1380 children aged 6 and 14 years, respectively. In addition, 689 children were assessed at both ages.

Using previously defined phenotypic data, the team assessed vitamin D levels as a risk modifier for respiratory and allergic outcomes at both ages. The predictive value of vitamin D levels at 6 years of age for development of a clinical phenotype at age 14 years was also examined.

Analysis of serum vitamin D levels from children aged 14 years showed that levels were lowest in midwinter and in spring, and rose to a peak around midsummer. Indeed, vitamin D deficiency was significantly more common in winter (9.4%) than in spring (5.5%).

When the researchers overlayed plots of mean house dust mite (HDM) allergen-specific immunology E (IgE) and serum vitamin D levels, they found an inverse correlation between the allergen and vitamin D levels.
Indeed, adolescents without sufficient vitamin D at 14 years of age had a significantly higher prevalence of BHR and atopy, with HDM sensitization the most significant marker.

Boys presented significantly more allergic conditions than girls, including atopy (65.2 vs 54.4%), HDM sensitization (43.6 vs 34.4%), and poor lung function (10.0 vs 4.8%).

Furthermore, inverse relationships between vitamin D status and the prevalence of allergic clinical conditions was only observed among boys. Compared with boys with sufficient vitamin D levels, those without sufficient levels had a significantly increased frequency of BHR (19.6 vs 13.3%), atopy (72.2 vs 61.1%), and HDM sensitization (50.2 vs 39.8%).

Analysis of samples from children aged 6 years revealed that vitamin D levels correlated significantly with those at 14 years. The stronger associations found in boys at age 14 years were also present at age 6 years.
Notably, low vitamin D levels at age 6 years were associated with an increased risk for atopy but not BHR at 14 years.

"Future studies with longitudinal birth cohorts are needed to determine how vitamin D status in early life and throughout childhood modifies risks of asthma, allergy, and related conditions," conclude the authors in the European Respiratory Journal.

By Ingrid Grasmo

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