Exposure to light at night and risk of depression in the elderly

Jul 17, 2013Journal of affective disorders

Nighttime light exposure and depression risk in older adults

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Abstract

The median nighttime light intensity measured in 516 elderly individuals was 0.8 lx.

Higher prevalence of light at night exposure was observed in individuals with depressive symptoms compared to those without.
Depressed individuals had an average nighttime light intensity of ≥ 5 lx, associated with an adjusted odds ratio of 1.89 for depression.
The duration of nighttime light exposure at intensity ≥ 10 lx for at least 30 minutes was also more common in the depressed group, with an adjusted odds ratio of 1.71.
No significant association was found between overnight urinary melatonin excretion and depressive symptoms.
The findings suggest that reducing nighttime light exposure in home settings may be linked to lower depressive symptoms in the elderly.

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BACKGROUND: Recent advances in understanding the fundamental links between chronobiology and depressive disorders have enabled exploring novel risk factors for depression in the field of biological rhythms. Increased exposure to light at night (LAN) is common in modern life, and LAN exposure is associated with circadian misalignment. However, whether LAN exposure in home settings is associated with depression remains unclear.

METHODS: We measured the intensities of nighttime bedroom light and ambulatory daytime light along with overnight urinary melatonin excretion (UME) in 516 elderly individuals (mean age, 72.8). Depressive symptoms were assessed using the Geriatric Depression Scale.

RESULTS: The median nighttime light intensity was 0.8lx (interquartile range, 0.2-3.3). The depressed group (n=101) revealed significantly higher prevalence of LAN exposure (average intensity, ≥ 5 lx) compared with that of the nondepressed group (n=415) using a multivariate logistic regression model adjusted for daytime light exposure, insomnia, hypertension, sleep duration, and physical activity [adjusted odds ratio (OR): 1.89; 95% confidence interval (CI), 1.10-3.25; P=0.02]. Consistently, another parameter of LAN exposure (duration of intensity ≥ 10 lx, ≥ 30 min) was significantly more prevalent in the depressed than in the nondepressed group (adjusted OR: 1.71; 95% CI, 1.01-2.89; P=0.046). In contrast, UME was not significantly associated with depressive symptoms.

LIMITATION: Cross-sectional analysis.

CONCLUSION: These results suggested that LAN exposure in home settings is significantly associated with depressive symptoms in the general elderly population. The risk of depression may be reduced by keeping nighttime bedroom dark.

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Exposure to light at night and risk of depression in the elderly

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