We already know that some sleep patterns and changes seem to be linked to dementia, though it can be hard to work out in which way the relationship lies: maybe it’s a symptom of the condition, or maybe it increases risk. It could be a mix of both.
But a new study has found that a daytime factor could play a role in our likelihood of developing dementia, too.
According to a paper published in General Psychiatry, our daytime light exposure might matter, too.
Bright daytime light appears to be linked with lower dementia risk
Researchers looked at the amount of light 87,577 participants – who wore wristwatches with light sensors – got in a typical week.
Then, they followed the participants’ health data over about eight years.
During this time, 741 of the people involved in the study developed dementia (none of them had the condition at the start).
The scientists then compared those results with people’s watch-tracked light exposure levels from years ago.
After looking at both metrics, it seemed that those who got at least 42 minutes of light over 1000 lux – about as bright as a cloudy sky, but much more illuminating than indoor lights, which tend to sit around 500 lux in our most well-lit rooms – faced 17% less dementia risk.
The longer people spent in bright outdoor light during the day, the lower their likelihood of dementia seemed to be. Night owls, people carrying the dementia-linked APOE4 gene, and those exposed to more nighttime light also seemed to benefit more from daylight’s protective effects, too.
In a later analysis, researchers found that getting less than 42 minutes of daylight a day seemed to be a stronger predictor of dementia than factors like obesity, alcohol consumption, traumatic brain injury, and more.
While it has been associated with heart issues, this paper found that “Nighttime light showed no significant association with dementia risk”.
It could be down to our body’s natural clocks
The study also said that “CRARs and brain structures mediated up to 33% of the association” between bright daylight and dementia risk.
CRAR stands for “circadian rest–activity rhythms,” or our body’s natural sleep-wake cycle.
We know that natural light, especially morning light, can help to keep this inner clock on track. A separate paper found that turning off a circadian protein in mice reduced their levels of tau protein, the accumulation of which in the brain is linked to dementia.
However, the daylight study only found a link, and not a cause. In other words, it didn’t prove that daylight definitely decreased dementia risk.
Still, it suggests that if further research backs this finding up, future studies may “position daytime light exposure as a novel, robust and measurable indicator of dementia risk”.
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