• asthma;
  • breastfeeding;
  • fast food consumption;
  • sex


Background Fast food consumption and childhood asthma have rapidly increased in recent decades. During the same period there has been an increased rate of prolonged breastfeeding.

Objective To evaluate if fast food consumption was associated with asthma in children, and if the proposed protective effect of breastfeeding on asthma was altered by fast food consumption.

Methods This case–control study included 246 children with allergist-diagnosed asthma and 477 non-asthmatic controls at age 8–10 years. Information on fast food consumption and exclusive breastfeeding was obtained from questionnaire data. The association between asthma and fast food consumption was evaluated. Asthma in relation to exclusive breastfeeding was also evaluated, taking into account fast food consumption as a modifying factor.

Results Children with asthma were more likely to consume fast food than children without asthma [crude odds ratio (OR) 1.70, 95% confidence interval (CI) 1.23–2.34]. In comparison to prolonged exclusive breastfeeding (geqslant R: gt-or-equal, slanted12 weeks), asthma was positively associated with short-term exclusive breastfeeding (<12 weeks) in children who never or occasionally consumed fast food (crude OR 1.84, 95% CI 1.09–3.11), but not in children who frequently consumed fast food (crude OR 1.07, 95% CI 0.72–1.61). The P-value for this interaction (0.109) was borderline. Children with high fast food consumption who were exclusively breastfed <12 weeks as infants, had greater than a twofold risk of asthma compared with infants who had been exclusively breastfed for a longer time period and who did not become high consumers of fast food in later childhood. These findings were not affected after final adjustment of confounders and covariates.

Conclusion Fast food consumption is associated with asthma in children and potentially counteracts the protective effect of prolonged breastfeeding on asthma. This may explain the paradoxical phenomenon of parallel increased rates of prolonged breastfeeding and asthma in children.