Why does this study matter?
As we get older, sleep quality suffers, and poor sleep can lead to poor overall health. Our circadian function plays a major role in the quality of our sleep, and research suggests that the physical environment can support better circadian function. For example, lighting solutions may be able to make an important difference for aging populations, who experience reduced light transmission through the ocular lens. Some research shows that residents with dementia in care homes experienced better sleep when exposed to increased light levels. There is some evidence that suggests an increase in the amount of high color temperature “blue light” may make up for the aging eye’s reduced responsiveness to short wavelength (blue) light.
How was the study done?
Based on this background information, Hopkins and colleagues set out to compare the effects of blue-enriched white light (17000 K) with low temperature color white light (4000 K) on older people’s mood, alertness, rest-activity, and sleep. The authors believe this to be the first study to look at the effect on a general population of older people not diagnosed with dementia.
The lighting was installed in communal lounges and dining rooms across seven British care home study sites that were selected for their similarity in environmental characteristics. The researchers compared two care homes at a time over the course of eleven weeks each, swapping the order of the experimental blue-enriched light and the control condition white light – a randomized crossover study design. Each site had four weeks of blue-enriched white lighting and four weeks of white lighting, separated by three weeks of “wash-out” (under the care homes’ own light).
Data for 80 residents were gathered using several subjective self-reported (mood, sleep, alertness) and objective (rest activity rhythms, performance) measures. Residents completed questionnaires and cognitive and motor tasks. Researchers observed resident behavior, assessed circadian rhythms through sleep analysis, and gathered sleep times through wearable software. A subset of participants also received anxiety and depression evaluations. Analysis considered resident age (years), mobility level, and certain medications, but these were not significant in the modelling of the outcomes.
Study results showed two beneficial outcomes of blue-enriched lights: increased daytime activity and reduced subjective anxiety. However, there were numerous drawbacks. Objective sleep analysis showed that the blue-enriched lights significantly increased actual wake time (following sleep onset) and activity during sleep, while decreasing actual sleep time, sleep percentage, and sleep efficiency. Subjective sleep quality also suffered. There was no difference in daytime alertness and performance, depression, or the time to go from fully awake to asleep (sleep latency).
Can we say the results are definitive?
Researchers acknowledged a gender imbalance in participants (69 female, 11 male). Although this may be appropriate, as care home residents tend to be female, this did not allow for gender comparisons. Another potential issue is that participants were free to come and go as they pleased from the experimental and other areas of the care center. This allowed for more natural behavior of residents than in previous studies where participants were exposed to lighting conditions for set periods, but made it difficult to control for lighting conditions participants may have been exposed to outside of the experimental area.
The authors also mentioned that the study period may have been too short for any permanent behavior changes to take place and that the relatively small difference in light intensity (as compared to other studies) may also have affected the results.
Older people already suffer from poor sleep, and the findings in this study show that blue-enriched white light may exacerbate that problem, at least in the short-term. While reduced anxiety is certainly a positive outcome, and increased daytime activity may be beneficial, these effects may be outweighed by the health consequences of the negative outcomes found.
What’s the takeaway?
Study results show mixed short-term results of blue-enriched lighting for older people in care homes. Positive effects included increased daytime activity and reduced anxiety, and negative effects included increased night-time activity, reduced sleep efficiency, and lessened sleep quality. All of the differences were small.
Lighting affects different people in different ways. A lighting type that improves one person’s circadian rhythm may have a negative effect or no effect for someone else. This study’s findings provide some helpful insight in an area of growing interest, but further research is needed to better understand the effects of specific lighting types on various populations.
Hopkins, S., Morgan, P. L., Schlangen, L. J. M., Williams, P., Skene, D. J., & Middleton, B. (2017). Blue-enriched lighting for older people living in care homes: Effect on activity, actigraphic sleep, mood and alertness. Current Alzheimer Research, 14(10), 1053–1062. https://doi.org/10.2174/1567205014666170608091119
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