Sleep quality and the cortisol awakening response (CAR) among law enforcement officers: The moderating role of leisure time physical activity

Abstract

Objective: The goal of this study was to investigate the role of leisure time physical activity (LTPA) on the association between sleep quality and the cortisol awakening response (CAR) in people with an occupation that exposes them to high levels of stress.

Methods: Participants were 275 police officers (age = 42 years ± 8.3, 27% women) enrolled in the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) study (conducted between 2004 and 2009). Officers provided four salivary cortisol samples (on awakening and 15, 30, and 45 min after awakening). Hours of leisure time physical activity were assessed using the Seven-Day Physical Activity Recall questionnaire. Sleep quality (good/poor) was evaluated using the Pittsburgh Sleep Quality Index (PSQI) scale. Analysis of covariance and repeated measures models were used to examine the association of sleep quality to the two aspects of CAR: cortisol levels (total area under the curve (AUC_G), mean, and peak cortisol) and cortisol profiles (the overall pattern in cortisol level during the 45 min period following awakening, the increase in cortisol from baseline to average of post awakening values (mean increase), and area under the curve with respect to increase (AUC_I)). Analyses were stratified by participant level of reported LTPA (sufficiently vs. insufficiently active, defined as ≥ 150 vs. < 150 min/week of moderate intensity activity, respectively). Since cortisol activity is known to be influenced by gender, we conducted additional analyses also stratified by gender.

Results: Overall, results demonstrated that LTPA significantly moderated the association of sleep quality with CAR. Among participants who were sufficiently active, CAR did not differ by sleep quality. However, in those who were insufficiently active during their leisure time, poor sleep quality was associated with a significantly reduced level of total awakening cortisol secretion (AUC_G (a.u.) = 777.4 ± 56 vs. 606.5 ± 45, p = 0.02; mean cortisol (nmol/l) = 16.7 ± 1.2 vs. 13.3 ± 0.9, p = 0.03; peak cortisol (nmol/l) = 24.0 ± 1.8 vs. 18.9 ± 1.5, p = 0.03 for good vs. poor sleep quality, respectively). The normal rise in cortisol after awakening was also significantly lower in inactive officers with poor sleep quality than in those with good sleep quality (mean increase (nmol/l) = 6.7 ± 1.5 vs. 2.3 ± 1.2, p = 0.03; AUC_I (a.u.) = 249.3 ± 55 vs. 83.3 ± 44, p = 0.02 for those with good vs. poor sleep quality, respectively). While findings for male officers were consistent with the overall results, CAR did not differ by sleep quality in female officers regardless of LTPA level.

Conclusion: Findings of this study suggest that poor sleep quality is associated with diminished awakening cortisol levels and dysregulated cortisol patterns over time, but only among officers who were inactive or insufficiently active during their leisure time. In contrast, sleep quality was not associated with any measures of CAR in officers who reported sufficient activity, suggesting a potential protective effect of LTPA. In analyses stratified by gender, findings for male officers were similar to those in the pooled sample, although we found no evidence for a modifying effect of LTPA in women. Future longitudinal studies in a larger population are needed to confirm these findings and further elucidate the relationships between LTPA, sleep quality, and cortisol response.

Keywords: CAR; Cortisol awakening response; HPA axis; Physical activity; Pittsburgh Sleep Quality Index; Police officers.

Fig. 1.

Sketch illustrating the various CAR indices: (1) total area under the curve (AUC_G: area of the region under the curve to the ground), (2) area under the curve with respect to increase (AUC_I: shaded portion), (3) average of the four cortisol measurements (AVE), (4) the peak value (PK), (5) time from baseline to peak (TBP), (6) decline in cortisol following peak (DCFP), and (7) the post-awakening increase in cortisol (30Inc, PkInc, and MnInc). Note that in this particular sketch, 30Inc and PkInc are identical because the peak also happen to occur at AC30.

Fig. 2.

Sample size tracing for analysis of sleep quality (SQ), leisure time physical activity (LTPA), and CAR: The BCOPS baseline study.

Fig. 3.

Pooled sample. Awakening cortisol profile by sleep quality stratified by LTPA levels showing significant differences in pattern and total cortisol secretion by sleep quality only among those who were inactive or insufficiently active.

Fig. 4.

Stratified by gender. Awakening cortisol profile by sleep quality stratified by gender and LTPA levels; among men significant differences in profile and total cortisol secretion by sleep quality were observed only in those who were inactive or insufficiently active while among women there were no significant differences in either pattern or total cortisol secretion by sleep quality regardless of LTPA.

Fig. 5.

Pooled sample. Awakening cortisol profile by CAR responder status stratified by LTPA levels and sleep quality showing significant differences in pattern by CAR responder status where non-responders exhibited inverted pattern regardless of LTPA and sleep quality.