A new study funded by the National Institutes of Health, US,  is exploring the effects of L-citrulline, an amino acid available over the counter, on asthma symptoms in people with obesity. The research is co-led by Dr Fernando Holguin, a professor of pulmonary sciences and critical care at the University of Colorado School of Medicine, who first researched on how and why obesity makes asthma symptoms worse, and what therapeutics may mediate these effects. The present study is an expansion of a proof-of-concept study Dr Holguin led earlier that demonstrated L-citrulline increases nitric oxide levels, improved lung function and decreased asthma symptoms.