Dr. Litonjua's research primarily deals with investigating factors that both increase and decrease the risk of developing asthma, wheezing, and allergic disorders in childhood. As part of this, he has investigated a broad range of prenatal and early life exposures including maternal diet, exposure to allergens, exposure to early life environment (e.g. pets, daycare attendance, air pollution, etc). He co-led a clinical trial of vitamin D supplementation in pregnancy to prevent asthma in the offspring.