Increased airway inflammation at night contributes to the nocturnal worsening of asthma. In vitro studies have shown exogenous melatonin to be pro-inflammatory in asthma, but it is unknown whether endogenous melatonin levels are a controller of airway inflammation in nocturnal asthma.

Our aim was to determine 24-hour patterns of serum melatonin and their relationship to overnight decline in physiology in subjects with nocturnal asthma, non-nocturnal asthma, and in healthy controls.

Observational study of pulmonary physiology and melatonin levels in patients with nocturnal asthma (n = 7), non-nocturnal asthma (n = 13), and healthy controls (n = 11). Subjects maintained a constant sleep–wake regimen for 7 days. On day 8, serum melatonin was measured every 2 hours by radioimmunoassay and analyzed by cosinor modeling. The correlation between serum melatonin levels and overnight change in spirometry was evaluated by Spearman's rank correlation analysis.

In subjects with nocturnal asthma, peak melatonin levels were significantly elevated compared with healthy controls (67.6 ± 5.0 pg/mL versus 53.5 ± 4.0 pg/mL, P = .03). Melatonin acrophase was delayed in nocturnal asthma (02:54 versus 01:58 in healthy controls, P = .003, and 02:15 in non-nocturnal asthma, P = .01). In subjects with nocturnal asthma, increasing melatonin levels were significantly and inversely correlated with overnight change in FEV₁ (r = −.79, P = .04), a relationship that was not observed in non-nocturnal asthma or healthy controls.

Nocturnal asthma is associated with elevation and phase delay of peak serum melatonin levels. Elevated melatonin levels might contribute to the pathogenesis of nocturnal asthma.