He received his medical degree from the University of the Philippines Manila (Manila, Philippines). He then completed a fellowship in internal medicine and a chief medical residency at The Brooklyn Hospital Center (formerly Brooklyn Hospital and Brooklyn - Caledonian Hospital). He also completed two fellowships: the first in pulmonary and critical care at West Virginia University Hospitals, and the second in pulmonary disease at BWH. He is board certified in critical care medicine, internal medicine and pulmonary disease.
Dr. Litonjua's clinical interests include chronic obstructive pulmonary disease and asthma. His research examines the ways in which environmental exposures and genetic factors impact the development of asthma and lung function decline. He is currently studying the impact of vitamin D on lung disease, and his publications were the first to demonstrate that higher maternal vitamin D intake during pregnancy protects against lung-related illnesses in children. Dr. Litonjua has authored over 200 peer-reviewed publications and is the recipient of funding from the National Institutes of Health.