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Table. Risk factors and protective factors for developing asthma

Life stage Exposure Effect on asthma risk*
Low maternal vitamin D level Probably increased
Maternal obesity Probably increased
Maternal smoking Probably increased
Maternal paracetamol use Possibly increased
Maternal antibiotic use Possibly increased
Maternal vitamin E intake Possibly reduced
Genotype Increased
Cigarette smoke Probably increased
Breastfeeding Possibly reduced

Low birth weight Probably increased
Pre-term delivery Probably increased
Delivery by Caesarean section Possibly increased
Neonatal jaundice Possibly increased

Outdoor air pollution Probably increased
Moulds Probably increased
Exposure to allergens to which sensitised Probably increased
Cigarette smoke Probably increased
Obesity Possibly increased
Antibiotics Possibly increased
Paracetamol Possibly increased
Proton pump inhibitors Possibly increased
H2 receptor antagonist  Possibly increased
Pets (if not sensitised) Possibly reduced
Dietary antioxidants, fruits, vegetables Possibly reduced
Mediterranean diet Possibly reduced
Farming lifestyle Possibly reduced

Respiratory syncytial virus infection Possibly increased
Human rhinovirus infection Possibly increased
Antibiotics (where unavoidable) Possibly increased
Reduced diversity of intestinal microbiota Possibly increased

Airborne sensitisers or irritants in workplace or home  Increased
Ryegrass pollen (high concentration associated with springtime thunderstorm in sensitised individual)§  Probably increased
Cigarette smoke  Possibly increased
Pesticides  Possibly increased
Low physical activity  Possibly increased
Fish consumption  Possibly reduced
Dietary polyunsaturated fatty acids  Possibly reduced
Dietary antioxidants, fruits, vegetables  Possibly reduced
Mediterranean diet  Possibly reduced


*Summary of overall effects based on currently available evidence

§ Exposure to outdoor air with high concentrations of ryegrass pollen immediately preceding  a springtime thunderstorm has been associated with new-onset asthma in people with seasonal allergic rhinitis sensitised to ryegrass pollen.


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