Diurnal patterns of salivary cortisol and cortisone output in chronic fatigue syndrome

Abstract

Background The aim of the present study was to obtain a naturalistic measure of diurnal hypothalamic–pituitary–adrenal (HPA) axis output in CFS patients unaffected by medication or comorbid psychiatric disorder likely to influence the axis. Method Cortisol and cortisone levels were measured in saliva samples collected from 0600 h to 2100 h at 3-h intervals in CFS patients and healthy controls. Results Mean cortisol and cortisone concentrations were significantly lower in patients than controls across the whole day, as were levels at each individual time point except 2100 h. Cosinor analysis showed a significant diurnal rhythm of cortisol and cortisone that was not phase-shifted in CFS compared to controls. However, there was a lower rhythm-adjusted mean and a lower amplitude in CFS patients. The cortisol/cortisone ratio showed no diurnal rhythm and did not differ between CFS subjects and controls. Limitations The sample size was relatively small, and drawn from specialist referral patients who had been ill for some time; generalisation of these results to other populations is therefore unwarranted. Conclusion The main findings of this study are to provide further evidence for reduced basal HPA axis function in at least some patients with CFS and to show for the first time that salivary cortisone is also reduced in CFS and has a diurnal rhythm similar to that of cortisol. We have also demonstrated that the cortisol/cortisone ratio remains unchanged in CFS, suggesting that increased conversion of cortisol to cortisone cannot account for the observed lowering of salivary cortisol.