The cortisol awakening response (CAR) across the female menstrual cycle

The cortisol awakening response (CAR) has been established as a useful marker of hypothalamus-pituitary-adrenal (HPA) axis activity and has become a standard tool for stress research in ambulatory settings. Although much knowledge has been accumulated on a variety of factors modulating the CAR, the impact of the female menstrual cycle, especially during ovulation, still remains unclear. To the best of our knowledge, this is the first study that measured the CAR during menses, the follicular phase, ovulation and the luteal phase in a repeated measurement design. For this purpose, a final sample of 29 naturally cycling, healthy, non-smoking, and medication-free women collected saliva samples directly after awakening as well as 30, 45, and 60 min later during each of the four different phases. To determine the timing of ovulation, an ambulatory chromatographic ovulation test kit was applied. A repeated measurements ANOVA resulted in a significant interaction effect sample × cycle phase (p=0.04), with the highest awakening response during ovulation. While awakening cortisol levels were comparable across the four cycle phases (p=n.s.), the net increase was significantly elevated during ovulation (p=0.05). Our data also confirmed earlier cross-sectional results reporting no differences in the CAR between the follicular and luteal phase. Finally, a concurrent assessment of mood applying the POMS (Profile of Mood States) yielded no differences across the four cycle phases (all p=n.s.). In sum, the present data points to the idea that the CAR is elevated during ovulation, an effect which is presumably mediated by elevated sex steroid levels during the ovulation period.