Diurnal cortisol variation is associated with nocturnal blood pressure dipping

Objective: To investigate if diurnal cortisol variation is associated with nocturnal blood pressure (BP) dipping. Methods: In this study, 302 healthy adults (51% female; average age 31 years) underwent 24-hour ambulatory BP assessment with BP measured randomly approximately every 20 minutes during waking hours and every hour during sleep. Salivary cortisol was obtained at five time points. Cortisol and BP have natural diurnal variations and disruptions in these diurnal variations are related to pathological conditions, such as greater risk for cardiovascular disease. A lack of a drop in cortisol from day to night and a lack of a drop in BP from waking to sleeping have both been associated with negative outcomes. It is not known, however, if diumal variations in cortisol and BP are related, or if changes in cortisol from day to night influence BP dipping. Results: Diurnal cortisol variation was a significant predictor of BP dipping. Controlling for gender, body mass index, age, phase of menstrual cycle, sleep quality, morning cortisol, and daytime measures of the relevant cardiovascular assessments did not significantly affect the results. Cortisol variation was found to have a stronger relationship with BP dipping than any of the covariates measured. Conclusion: Decreased diurnal variation in cortisol is associated with decreased diumal variation in BP. Future studies could benefit from examining how these two variables interact in predicting disease outcomes. Key words: ambulatory blood pressure, cortisol, circadian rhythm, cardiovascular functioning, health.