Long-term high need for recovery is related to decreased diurnal cortisol variability

Introduction
Chronic stress, particularly combined with a lack of recovery, has been shown to lead to reduced subjective health. Long-term sustained stress activation may alter the feed-back system of the HPA axis, resulting in a lesser flexibility, which may appear as a flattened variability over the day. The aim of the present study was to examine whether a lack of recovery, as expressed by experiencing a need for recovery over an extended period of time, was associated with flattened cortisol variability.

Methods
In a three-wave study during a five-year period 176 men and women, aged 51 (23-65) years completed the first two sampling waves and 112 all three. They responded to a questionnaire, and sampled salivary cortisol at morning awakening, at + 30 minutes and at 9 p.m. One item assessed whether “Long” (> 1 day) or “Short” (1 day or less) time was needed to feel recovered after a work week (GROUP), which together with sampling wave (TIME) were used as factors in analyses including the interaction GROUP x TIME. The variable Cortisol Decline over the Day (CDD) was computed as the difference between the maximal morning concentration and the evening concentration and used as outcome. The two and three wave conditions were analysed separately.

Results
In the two-wave condition a GROUP x TIME interaction (p=.04), indicated a flattening CDD over time in those needing Long recovery. In the three-wave condition there were main effects of TIME (p=.01) and of GROUP (p=.02), but the interaction TIME x GROUP did not reach significance (p=.12). High job demands were related to a flatter CDD and need for long recovery, but did not affect the interaction TIME x GROUP.

Discussion
A need for long recovery after the work week may over time be associated to a low or decreasing flexibility in the HPA axis.