Spending more time in daylight could play a role in lowering the risk of developing dementia later in life, according to new research.
Scientists analysing data from nearly 87,600 adults found a consistent link between higher levels of daytime light exposure and a reduced likelihood of developing the condition.
The study, carried out by researchers at universities in China and published in the journal General Psychiatry, followed participants for around eight years. The average age was 62, and all wore wrist-worn devices measuring both movement and light exposure.
Over the course of the study, 741 participants were diagnosed with dementia.
Researchers found that people spending more time in brighter environments during the day had a significantly lower risk of developing the condition compared with those in dimly lit indoor settings.
Those exposed to average daytime light levels above 1,000 lux — roughly equivalent to a brightly lit indoor space or an overcast day outdoors — had a 16 per cent lower risk of dementia.
Spending around 1.5 hours a day in light above 3,000 lux, similar to outdoor daylight, was associated with an 18 per cent reduction in risk, while 40 to 45 minutes in very bright light above 7,000 lux was linked to a 17 per cent decrease, reports the Daily Mail.
Overall, spending less than 0.7 hours a day in bright daylight emerged as a stronger predictor of dementia risk than several established factors, including obesity, alcohol consumption and traumatic brain injury.
The protective effect of daylight was even more pronounced in people exposed to higher levels of light during the night, which is known to disrupt sleep patterns. Poor sleep quality has itself been linked to dementia risk.
Researchers said that even among those exposed to more light at night, higher daytime light levels were still associated with a 30 to 38 per cent lower risk of dementia.
The effect was also seen in so-called “night owls”, with those who received more daylight showing a 40 per cent reduction in risk.
Even individuals carrying a genetic mutation associated with a higher risk of Alzheimer’s disease showed a benefit, with daytime light exposure linked to a 19 to 27 per cent lower risk.
The researchers said light exposure acts as a key signal for the body’s circadian rhythm — the internal 24-hour clock that regulates sleep, alertness and cognitive function.
While the study shows an association rather than cause and effect, the authors said the findings suggest light exposure could become a useful marker in future dementia research.
They added that increasing daytime light exposure could potentially support brain health by improving circadian rhythm function and sleep quality.
Researchers also suggested possible biological mechanisms, including the role of disrupted circadian rhythms in neurodegenerative disease and early evidence that light exposure may help slow brain volume loss linked to dementia.
However, they stressed that more research is needed before any firm conclusions can be drawn.