PROSPECTIVE COHORT STUDY OF BREASTFEEDING AND THE RISK OF ASTHMA AT 7 YEARS
Anne Kristine Lossius, LIS *(SØF), Maria Christine Magnus (FHI), Jon Lunde (SØF), Ketil Størdal (SØF, FHI).
*Lege i Spesialisering på Barneavdelingen, SØF.
Abstract
Objectives:
We studied if duration of breastfeeding influences the risk of childhood asthma. Previous studies show conflicting results.
Methods:
The Norwegian Mother and Child Cohort Study (MoBa) is a prospective birth cohort study, which recruited pregnant women 1999-2008. We studied 72950 children with complete data of breastfeeding up to 18 months. The primary outcome was asthma at 7 years defined from a questionnaire (MoBa) which combined asthma symptoms with the use of asthma medications within the last year (n=30047). As a secondary outcome, we defined asthma by ≥2 filled prescriptions of asthma medications from the Norwegian Prescription Database (NorPD, n=41649) to include those without returned questionnaires. We calculated relative risks adjusted for gender, mode of delivery, gestational age and maternal asthma, pre-pregnant BMI, smoking and education.
Results:
Of the children fully breastfed for 6 months, 4.8% had asthma, compared to 5.0% of those breastfed but introduced to complementary foods. Infants breastfed at 6 months, but introduced to complementary foods <4 months and 4-6 months, had an adjusted relative risk (aRR) of 1.11(95% CI 0.94-1.33) and 0.98(0.83-1.16) compared to those fully breastfed, respectively.
Of infants breastfed <6 months, 6.8% had asthma, compared to 5.0% of infants breastfed ≥12 months (aRR 1.16, 1.02-1.33), whereas 4.9% of those breastfed 6-11 months had asthma (aRR 0.95, 0.85-1.06).
In secondary analysis using NorPD, 5.8% of infants breastfed <6 months (aRR 1.06, 0.94-1.20), and 4.6% breastfed 6-11 months (aRR 0.96, 0.87-1.06) compared to 4.6% of infants breastfed ≥12 months had asthma at 7 years.
Conclusions:
The age for introduction of complementary foods was not associated to asthma at 7 years in infants breastfed at 6 months. The risk of asthma was significantly higher in the group breastfed <6 months compared to ≥12 months. This association was not significant when participants not responding to questionnaires were included.