New research claims that exposure to outdoor light at night can reduce the incidence of Alzheimer’s disease disease, especially in people under the age of 65.
The researchers who conducted the study, funded by a National Institutes of Health grant and published in the journal Frontiers in Neuroscience on Friday, said they found correlations between areas of the US with excessive exposure to artificial light at night and the incidence of Alzheimer’s disease.
In the US, at least 19 states have legislation aimed at it reduce light pollutionbut the authors of the study say that despite this the “levels of light at night remain high in many parts of the country”.
While “street lights, road lighting and illuminated signs can deter crime, make roads safer and improve landscaping”, however, uninterrupted light has “ecological, behavioral and health consequences”, the authors said.
For this study, the researchers evaluated the prevalence of Alzheimer’s disease by looking at the average nighttime light intensity by state and county in the US from 2012 to 2018, using satellite-derived light pollution data and Medicare data reports of Alzheimer’s incidence. They also included medical data on variables known or believed to be risk factors for Alzheimer’s disease in their analysis, they said.
While conditions such as diabetes, hypertension and others were more strongly associated with the occurrence of Alzheimer’s disease than the intensity of night light, the authors said that night light was more strongly associated with the occurrence of Alzheimer’s disease than “alcohol abuse, chronic kidney disease, depression, heart failure , and obesity”.
For people under 65, nighttime light exposure was more strongly associated with Alzheimer’s incidence than any other disease factor examined in the study.
“This may suggest that younger people may be particularly sensitive to the effects of light exposure at night,” the researchers said.
Dr. Robin Voigt-Zuwala, an associate professor at Rush University Medical Center, and one of the authors of the research paper, explained: “Certain genotypes, which influence early onset Alzheimer’s disease, have an impact on the response to biological stressors which may account for increased vulnerability to the effects of nighttime light exposure,” adding that younger people are also more likely to “live in urban areas and have lifestyles that may increase exposure to light at night.”
Voigt-Zuwala said she believes that light is the “biggest factor” that influences circadian rhythms – our internal clock in our brain that indicates when to be awake or asleep by responding to light changes in our environment.
Exposure to light at night disrupts those rhythms, which Voigt-Zuwala says has an impact on Alzheimer’s disease. The group’s research, she said, showed that disruption reduces resilience, essentially “making individuals more susceptible to disease”.
Samuel Gandy, an Alzheimer’s researcher at Mount Sinai in New York, said the general findings of the new study make sense, since “light controls the circadian rhythm and it controls sleep,” he said, adding that for Alzheimer’s, “bad sleep increases the risk.”.
Living in an area with more intense outdoor light at night is associated with shorter sleep duration, increased daytime sleepiness and dissatisfaction with sleep quality, the study said.
Dr Jason Karlawish, co-director of the Penn Memory Center at the University of Pennsylvania, who was not involved in the study, said: “One of the pillars of good quality brain health is protecting your brain over time from developing of dementia, is good quality sleep,” adding: “It was not a surprise to see that evening light exposure, which can disrupt sleep, was associated with dementia.”
But Karlawish did point out that the researchers themselves acknowledged some limitations and caveats about the study in their paper — including that the Medicare data came from individuals’ current residences, and not necessarily reflective of lifetime residences in these areas and exposure to light over time. .
Still, Karlawish said the study “reiterates the importance of one of the pillars of brain health”.
The authors also acknowledge in the paper that they evaluated the incidence, not the incidence, of Alzheimer’s, meaning they measured the proportion of a population that has a particular trait at a given time rather than the rate of new cases of a disease occurring in a population over a period of time.
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David Knopman, a clinical neurologist at the Mayo Clinic, expressed concern about the study’s methodology and pointed out factors he believed needed to be addressed.
Light exposure measured by satellites, he said, “does not take into account window shades or natural sunlight”, adding that the northern tier of the US “has more daylight hours in the summer and much less in the winter”.
Knopman mentioned that there were probably also health and socio-economic status-related differences not in question in the study; some rural areas have a lower number of doctors per capita and therefore lower rates of dementia diagnosis, but not necessarily less dementia.
Voigt-Zuwala agreed that there are “many limitations associated with a population-based study” and said that additional studies are needed to “understand how light in the home affected these outcomes”. The difference in daylight hours across the country is something she will “absolutely” take into account in future studies.
“Rural and urban areas have different levels of light pollution,” she said, adding that it was the “method of doing the county analysis” where she “compared counties with roughly the same population and population density to make this exact point speak”.
“The assumption is that in urban centers of roughly the same population and density, access to doctors, exposure to air pollution and other factors may be important,” she said. “However, this approach does not give us individual level data, so more studies are needed in the future.”
“There is still much to learn about this topic and I look forward to spearheading these efforts,” she added.
While the data from preclinical studies and this study suggest that exposure to light at night can affect Alzheimer’s disease, the study points out that additional studies evaluating clinical and population health are needed, including those looking at the impact of the “total outdoor and look indoors. night light exposure”.
The authors say they hope the research empowers people to “make easy lifestyle changes” such as using blackout curtains or sleeping with eye masks.
