TOPLINE:

Repetitive exposure to low-intensity incandescent lighting during morning hours vs exposure to higher-intensity fluorescent lighting was associated with increased cortisol levels throughout the day and reduced total sleep time in healthy individuals, mirroring findings in patients with depression, a new trial showed.

METHODOLOGY:

• In a trial of 20 healthy participants (mean age, 24.5 years; 50% women), half were randomly assigned to exposure to low-intensity incandescent lighting (2700 K, 55 lux, 12 melanopic lux) and the other half to higher-intensity fluorescent lighting (3500 K, 800 lux, 481 melanopic lux) for 4 hours (8:00-12:00) over six mornings in 2011.
• Sleep variables were measured using polysomnography. Urine and saliva samples were analyzed to measure cortisol and melatonin levels.
• Participants completed psychomotor vigilance tests and Visual Analog Scale ratings to assess sleepiness and sadness.

TAKEAWAY:

• Exposure to low-intensity incandescent lighting during pre-midday hours was associated with significantly increased urine cortisol levels in the evening (P = .004) and salivary cortisol levels in the afternoon (P = .03) compared to exposure to higher-intensity fluorescent lighting.
• Low-intensity lighting was also linked to a reduction in total sleep time by 25 minutes compared to baseline (P = .02) and a significant shift in slow-wave activity to later in the night (P = .02).
• Higher-intensity fluorescent lighting was associated with significantly increased REM sleep duration in the second half of the night compared to baseline (P = .009) and compared to low-intensity lighting (P = .02).
• Participants exposed to low-intensity lighting reported significantly higher subjective sleepiness and sadness (P = .02 for both) than those exposed to higher-intensity lighting. There were no significant differences in melatonin levels between groups.

IN PRACTICE:

“Sustained exposure to low-level incandescent lighting during pre-midday may result in disturbances of the HPA [hypothalamic-pituitary-adrenal] axis and sleep reminiscent to those reported in patients with depression,” the investigators wrote.

“Integrating natural daylight or bright artificial light into schools, workplaces, and residential settings (including nursing homes) could ameliorate this vulnerability,” they added.

SOURCE:

The study was led by Jan de Zeeuw, PhD, St Hedwig Hospital, Clinic for Sleep & Chronomedicine, Berlin, Germany. It was published online on November 10 in the Journal of Psychiatric Research.

LIMITATIONS:

The study had a small sample size and between-participants design, which limited statistical power. The investigators lacked control over the light environment outside the laboratory, with wrist-worn actigraphy watches often covered in early spring and not providing accurate light measures. Cortisol and melatonin levels in urine were not corrected for creatinine levels, although they were corrected for urine volume. 

DISCLOSURES:

The investigators reported having no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.