We’re officially entering the dark times, at least when it comes to sunlight – the days will keep getting shorter and shorter as we head toward the winter solstice.
That’s not just a bummer for our moods and energy levels. How much bright light you get during the day may even be linked to your risk of dementia.
A study published in General Psychiatry in June found a 16% reduction in dementia risk among people with higher daytime light exposure.
Researchers also observed that getting less than 42 minutes a day of bright daylight was a better predictor of dementia than six established risk factors: alcohol consumption, obesity, hearing loss, traumatic brain injury, air pollution and vitamin D supplement use.
These findings are based on data from 87,577 dementia-free adults in the UK, who had an average age of about 62. Participants wore wrist sensors for a week that measured their light exposure during the day and at night. According to health records, 741 participants developed dementia over a median follow-up of 8.1 years.
Those whose average daytime light exceeded 1,000 lux – about the brightness level of a typical overcast day – had a 16% lower risk of developing dementia compared with people at lower light exposure levels. The researchers adjusted for factors such as age, sex, education, lifestyle and health conditions.
Spending longer stretches in even brighter light, at least 5,000 lux, was linked to a further drop in dementia risk, while nighttime light exposure showed no significant connection to dementia.
Specifically, people who got more than 42 minutes a day of light at at least 5,000 lux had a 17% lower risk of dementia. And getting less than 42 minutes of that bright daytime light was a better predictor of dementia than the six aforementioned risk factors.
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Notably, the association between daytime light exposure and dementia risk was stronger among participants with higher nighttime light exposure, evening chronotypes (basically, night owls) and carriers of the APOE ε4 gene – a major genetic risk factor for Alzheimer’s disease. In those three groups, higher daytime light was linked to dementia risk reductions from roughly 19% up to 41%.
The study notes that bright light therapy has been used to improve symptoms in people diagnosed with dementia. But as study co-author Hongliang Feng of Guangzhou Medical University told MedPage Today: “This is the largest prospective cohort to date using objective wearable measurements to link routine, real-world daytime light exposure to reduced dementia risk in the general population.”
He and his fellow researchers suspect the body’s internal clock could play a role.
“The core pathway is circadian regulation,” Feng said, noting that bright daytime light helps keep our sleep-wake rhythms stable and thus may help protect areas of the brain linked to dementia.
This study does not prove that more daytime light prevents dementia. As the published research states, the participants were generally “healthier and less socioeconomically deprived than the general population, possibly limiting the generalisability of risk estimates.”
The one-week monitoring period and use of wrist sensors may not reflect long-term habits or the level of light that reaches the eyes. Additionally, the data was collected between the years 2014 and 2018 “before the widespread adoption of LED lighting and increased nighttime device use,” the study notes.
Further research is needed to confirm a protective effect from light exposure during the day on the risk of developing dementia. We do know that things like moving your body and stimulating your brain have a positive impact – and these habits can involve spending time outside in the sun as well.
So if additional findings back up the link between daytime light and dementia risk, this study may simply highlight another benefit to spending more time in bright light, whether that’s a walk outside or a brighter indoor space. As the researchers noted, “increasing daytime light exposure may be a simple and cost-free strategy to reduce dementia risk in both clinical and community settings.”
