The objective of this study is to investigate if maternal intake of vitamins A and D from food and dietary supplements during pregnancy, and infant supplementation with these vitamins, are associated with development of asthma in the offspring.

This study was conducted as part of the research project "Causal pathways for asthma" funded by the Norwegian Research Council (2013-2017). The overall objective was to study if different pregnancy and early life exposures affect the risk of asthma and allergic diseases in children, and if these exposures exert their effects through epigenetic mechanisms, more specifically DNA methylation.

For this project, including the current study, existing data from the Norwegian Mother and Child Study (MoBa file version 9, 115 398 children and 95 248 mothers) were linked with the Medical Birth Registry of Norway and the Norwegian Prescription Database. The MoBa study recruited pregnant women between 1999 and 2008, at approximately 18 weeks of gestation. Beginning 2002, women completed a food frequency questionnaire about dietary intake (food and supplements) in pregnancy. A panel of maternal plasma biomarkers, including plasma retinol and 25-hydroxyvitamin D2 and D3, was available for a random sample of around 3,000 women who gave birth in 2002 and 2003.

Inclusion Criteria:

Available maternal dietary intake data from pregnancy. Child turned 7 years by July 1st 2014.

Exclusion Criteria:

No maternal baseline questionnaire. Maternal energy intake <4,500 or > 20,000 kJ. No dietary supplement data. No linkage to national birth registry, or non-live births, or multiple births. Child death, or emigration, or unknown vital status.

The Norwegian Mother and Child Study is a population-based pregnancy cohort (births 1999-2009). Women were recruited nationwide (41% participation) around 18 weeks gestation. The current study included 61,676 eligible chidren born 2002-2007.

Data have been shared with collaborators.