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Int J Med Sci. 2019 Jan 1;16(1):125-134. doi: 10.7150/ijms.28863. eCollection 2019.

The Effects of Naturalistic Light on Diurnal Plasma Melatonin and Serum Cortisol Levels in Stroke Patients during Admission for Rehabilitation: A Randomized Controlled Trial.

Author information

1
Clinical Stroke Research Unit, Department of Neurology, Rigshospitalet, Faculty of Health Sciences, University of Copenhagen.
2
Department of Clinical Biochemistry, Rigshospitalet and Faculty of Health Sciences, University of Copenhagen.
3
Danish Center for Sleep Medicine, Department of Neurophysiology Rigshospitalet, Faculty of Health Sciences, University of Copenhagen.
4
Department of Ophthalmology, Rigshospitalet, Copenhagen University Hospital.
5
Department of diagnostic, Radiologic clinic, Rigshospitalet and Faculty of Health Sciences, University of Copenhagen.

Abstract

Background: Stroke patients admitted for rehabilitation often lack sufficient daytime blue light exposure due to the absence of natural light and are often exposed to light at unnatural time points. We hypothesized that artificial light imitating daylight, termed naturalistic light, would stabilize the circadian rhythm of plasma melatonin and serum cortisol levels among long-term hospitalized stroke patients. Methods: A quasi-randomized controlled trial. Stroke patients in need of rehabilitation were randomized between May 1, 2014, and June 1, 2015 to either a rehabilitation unit equipped entirely with always on naturalistic lighting (IU), or to a rehabilitation unit with standard indoor lighting (CU). At both inclusion and discharge after a hospital stay of at least 2 weeks, plasma melatonin and serum cortisol levels were measured every 4 hours over a 24-hour period. Circadian rhythm was estimated using cosinor analysis, and variance between time-points. Results: A total of 43 were able to participate in the blood collection. Normal diurnal rhythm of melatonin was disrupted at both inclusion and discharge. In the IU group, melatonin plasma levels were increased at discharge compared to inclusion (n = 23; median diff, 2.9; IQR: -1.0 to 9.9, p = 0.030) and rhythmicity evolved (n = 23; p = 0.007). In the CU group, melatonin plasma levels were similar between discharge and inclusion and no rhythmicity evolved. Overall, both patient groups showed normal cortisol diurnal rhythms at both inclusion and discharge. Conclusions: This study is the first to demonstrate elevated melatonin plasma levels and evolved rhythmicity due to stimulation with naturalistic light.

KEYWORDS:

circadian rhythm; cortisol; light; melatonin; rehabilitation; stroke

Conflict of interest statement

Competing Interests: The authors have declared that no competing interest exists.

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