Effects of nighttime low-frequency noise on the cortisol response to awakening and subjective sleep quality 

Abstract:
The effects of night-time exposure to traffic noise (TN) or low frequency noise (LFN) on the cortisol awakening response and subjective sleep quality were determined. Twelve male subjects slept for five consecutive nights in a noise-sleep laboratory. After one night of acclimatisation and one reference night, subjects were exposed to either TN (35dB LAeq, 50dB LAmax) or LFN (40dB LAeq) on alternating nights (with an additional reference night in between). Salivary free cortisol concentration was determined in saliva samples taken immediately at awakening and at three 15-minute intervals after awakening. The subjects completed questionnaires on mood and sleep quality. The awakening cortisol response on the reference nights showed a normal cortisol pattern. A significant interaction between night time exposure and time was found for the cortisol response upon awakening. The awakening cortisol response following exposure to LFN was attenuated at 30 minutes after awakening. Subjects took longer to fall asleep during exposure to LFN. Exposure to TN induced greater irritation. Cortisol levels at 30 minutes after awakening were related to ‘activity’ and ‘pleasantness’ in the morning after exposure to LFN. Cortisol levels 30 minutes after awakening were related to sleep quality after exposure to TN. This study thus showed that night time exposure to LFN may affect the cortisol response upon wake up and that lower cortisol levels after awakening were associated with subjective reports of lower sleep quality and mood.

Introduction:
… A major intrinsic marker of the circadian rhythm is the level of circulating corticosteriods derived from activity within the hypothalamus-pituitary-adrenal (HPA) axis. Acute activation of this same HPA axis also represents a major physiological response to environmental stressors. Thus the degree to which environmental stressors can impact upon the circadian rhythm becomes of interest. The cortisol response to awakening is an index of adrenocortical activity. Previous studies have shown that the amount of cortisol in saliva (a true reflection of circulating physiologically active, or free, cortisol) increases after awakening with a peak at about 30 minutes, after which it declines. The response is rather robust over weeks or months, but has also been found to be suppressed by the burnout syndrome and increased in high levels of work overload and in relation to unemployment stress. Environmental noise is a potential disruptor of the normal circadian pattern due to its effects on sleep and recreation. The effect of noise on the circadian rhythm of cortisol is not widely documented. …

The auditory system is permanently alert, even during sleep. Excitations of the system are subcortically connected via the amygdala to the HPA axis. Thus, noise can influence the release of different stress hormones, especially in sleeping persons during the early morning phase. … While the effects on sleep and well being of transportation noises are rather well documented, much less is known of effects on sleep caused by low frequency noise (< 200 Hz). Low frequency noise is common in both occupational and domestic environments. Several case studies and some epidemiological studies indicate that low frequency noise affects sleep quality, particularly with reference to the time taken to fall asleep and tiredness in the morning. …

Kerstin Persson Waye, Angela Clow, Sue Edwards, Frank Hucklebridge, Ragnar Rylander

Life Sciences 72 (2003) 863–875

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