IN some places around the world, the lights never go off.
From New York City to Tokyo, streetlights and illuminated signs can deter crime and make roads safer.
But uninterrupted light comes with ecological, behaviour and health consequences, scientists warn.
American researchers found that excessive light pollution during “dark hours” may increase someone’s risk of Alzheimer’s – especially in younger people.
In fact, they discovered exposure to outdoor light at night could increase the prevalence of dementia more than any other risk factors for people under 65.
Study first author Professor Robin Voigt-Zuwala, of Rush University Medical Centre, Chicago, said: “We show that in the US, there is a positive association between Alzheimer’s disease prevalence and exposure to light at night, particularly in those under the age of 65.
“Nightly light pollution – a modifiable environmental factor – may be an important risk factor for Alzheimer’s.”
The team studied light pollution maps for 48 US states and incorporated medical data about variables known or believed to be risk factors for Alzheimer’s in their analysis.
They generated night-time intensity data for every state and divided them into five groups, from lowest to highest night-time light intensity.
Their findings, published in the journal Frontiers in Neuroscience, showed that for people aged 65 and older, Alzheimer’s prevalence was more strongly correlated with nightly light pollution than some other disease factors – including alcohol abuse, chronic kidney disease, depression, and obesity.
Other risk factors – such as diabetes, high blood pressure, and stroke – were more strongly associated with Alzheimer’s than light pollution.
But for people under 65, the researchers found that higher night-time light intensity was associated with a greater Alzheimer’s prevalence than any other risk factor examined in the study.
The researchers say it could suggest that younger people may be “particularly sensitive” to the effects of light exposure at night.
It is unclear exactly why, but the team believe it could be due to individual differences in light sensitivity.
Prof Voigt-Zuwala said: “Certain genotypes, which influence early-onset Alzheimer’s, impact the response to biological stressors, which could account for increased vulnerability to the effects of night-time light exposure.
“Additionally, younger people are more likely to live in urban areas and have lifestyles that may increase exposure to light at night.”
The researchers hope that their findings can help educate people about the potential risks of light at night.
Prof Voigt-Zuwala said: “Awareness of the association should empower people – particularly those with risk factors for Alzheimer’s – to make easy lifestyle changes.”
She added: “Easy-to-implement changes include using blackout curtains or sleeping with eye masks.
“This is useful, especially for those living in areas with high light pollution.”
Eight in 10 people around the world are exposed to excessive or inappropriate use of artificial light outdoors.
But the researchers say light exposure inside the home could be just as important.
Although they didn’t examine the effects of indoor light in the study, the team said that blue light has the greatest impact on sleep, and using blue light filters, swapping to warm light, and installing dimmers in the home could effectively reduce light exposure.
Dementia – the most common form of which is Alzheimer’s – comes on slowly over time.
As the disease progresses, symptoms can become more severe.
But at the beginning, the symptoms can be subtle or mistaken for normal memory issues related to ageing.
The US National Institute on Aging gives some examples of what is considered normal forgetfulness in old age, and dementia disease.
You can refer to these above.
For example, it is normal for an ageing person to forget which word to use from time-to-time, but difficulting having conversation would be more indicative of dementia.
Katie Puckering, Head of Alzheimer’s Research UK’s Information Services team, previously told The Sun: “We quite commonly as humans put our car keys somewhere out of the ordinary and it takes longer for us to find them.
“As you get older, it takes longer for you to recall, or you really have to think; What was I doing? Where was I? What distracted me? Was it that I had to let the dog out? And then you find the keys by the back door.
“That process of retrieving the information is just a bit slower in people as they age.
“In dementia, someone may not be able to recall that information and what they did when they came into the house.
“What may also happen is they might put it somewhere it really doesn’t belong. For example, rather than putting the milk back in the fridge, they put the kettle in the fridge.”
