Changes in the hormone cortisol have been implicated in the pathogenesis of nocturnal worsening of asthma, or nocturnal asthma (NA). We studied 45 patients, 15 with NA, 15 subjects with non-nocturnal asthma (NNA), and 15 controls over a 24h period, measuring forced expiratory volume in 1 second (FEV1) and serum cortisol at 08:00, 12:00, 16:00, 20:00, 23:00, 04:00, and 08:00 the following day. Evaluation of the time response curves for cortisol revealed a significant difference in the shape of the curves (p = 0.04 by mixed-effects model). Evaluation of individual time points revealed that the cortisol levels in the NNA and control groups were significantly lower than in the NA group at 20:00 (NNA: 3.5 +/- 0.8 mg/mL;
Controls: 3.4 +/- 0.8 mg/mL; NA: 4.9 +/- 0.8 mg/mL; p = 0.007). The percentage (%) predicted FEV1 was significantly different among the three groups over the 24h period (p < 0.001). The percentage predicted FEV1 was significantly lower in the NA group compared to the control group at all time points and significantly lower than the NNA group at 16:00, 23:00, and 04:00. The difference among the groups was most pronounced at 04:00, when the percentage predicted FEV1 was 58.9 +/- 2.2% in the NA group, 76.8 +/- 2.9% in the NNA group, and 91.6 +/- 2.8% in the control group (p = 0.001, where each group is significantly different from the others). Although the time response curves for cortisol were significantly different among the three groups, the differences in serum levels of cortisol do not appear to be clinically significant. Therefore, serum levels of cortisol may not be the appropriate measurement to assess the role of cortisol in nocturnal asthma.