Light pollution linked with cognitive decline in a new study
Rapid urbanisation and suburban sprawl have brought with them increased outdoor artificial light at night (LAN), blocking our view of the stars, interrupting important nocturnal wildlife patterns, and according to a new study from our School researchers, increasing the risk of cognitive decline in the elderly.
Senior author Professor Yuming Guo, Head of our Climate Air Quality Research Unit, says growing evidence points to light pollution being a complex health problem. “Exposure to increased LAN has been linked with some cancers, cardiovascular diseases and metabolic disorders. The current body of evidence is weak but certainly growing – we wanted to understand whether it’s potentially a factor in cognitive decline, which is a big problem in ageing populations globally.”
The researchers looked specifically at whether exposure to LAN was associated with onset of mild cognitive impairment (MCI), a transition phase between normal ageing, and dementia and Alzheimer's disease in the elderly. Nearly half of diagnosed MCI cases progress to dementia within three years.
Prof Guo says, “We chose to focus on a cohort of Chinese veterans. China has 264 million people aged over 60 years, and veterans are provided with life-long healthcare, providing long-term and relatively comprehensive health records. So they are ideally situated for this type of study, and Chinese society has a lot to gain from such knowledge. It’s exciting, because this is the first study on light exposure and cognitive impairment done in that country.”
5,496 eligible participants from 277 veteran communities across 18 Chinese cities were included in the study. Participants were assessed using two mental capacity screening tools, with those indicating suspected MCI progressing to confirmation via neuropsychological evaluations, and clinical examination including physical examinations and neuroimaging scans.
Information on demographic characteristics, behavioral factors (such as diet, exercise, smoking status), and self-reported health status was collected using a standard questionnaire, and objective physical health information was drawn from health records.
Data on participants' exposure to outdoor LAN for the three years prior to their MCI assessment were extracted from the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS). The images capturing fractions of the light from the earth's surface can well represent the relative level of LAN illumination at the ground-level.
The findings showed that outdoor LAN was positively associated with higher risk of MCI in these veterans. The association was more pronounced among women, those with lower levels of formal education, and those with fewer regular social activities.
“Our findings add to mounting concerns about LAN exposure and mental health. While the precise biological mechanisms underpinning the association remain unclear, there is some speculation that disruption to circadian rhythms may influence brain ageing and the development of cognitive impairment.
“Other theories revolve around impairment of natural growth and development of neural tissue and neurotransmitters.
“Even without that knowledge, what is starting to be clear is that reducing LAN exposure where possible could be an effective way to lower the risk of MCI development in the first place. And just as importantly, reducing artificial LAN reduces carbon emissions, which slows climate change and brings countless health benefits along with it.”
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