Less than 42 minutes of bright daylight linked to higher dementia risk

The findings, published in General Psychiatry, point to daytime light exposure as a potentially overlooked factor in brain health.

Brighter Daylight Linked to Lower Dementia Risk

To investigate the connection, researchers analyzed data from 87,577 adults who wore wrist devices equipped with accelerometers. The devices allowed scientists to measure participants' exposure to light during both the day and night. Over a median follow-up period of 8.1 years, 741 participants developed dementia.

The results revealed a notable pattern. People exposed to average daytime light levels exceeding 1,000 lux (a moderately bright light level equivalent to an overcast day outdoors) had a 16% lower risk of developing dementia. Spending longer periods in even brighter daytime light (at least 5,000 lux) was associated with further reductions in risk.

Too Little Daylight Emerges as a Surprising Dementia Risk Indicator

One of the most striking findings involved people who received very little bright light during the day. Getting less than 0.7 hours, or 42 minutes, of bright daytime light daily was a stronger predictor of dementia than 6 established dementia risk factors.

Interestingly, researchers found no statistically significant connection between nighttime light exposure and dementia risk. This suggests that daytime brightness, rather than light exposure at night, may be particularly relevant to the relationship identified in the study.

"Daytime light exposure may serve as a novel indicator of dementia risk," said corresponding author Hongliang Feng, PhD, of Guangzhou Medical University, in China.

Although the findings reveal an association, they do not establish that getting more daylight directly prevents dementia. Instead, the research highlights daytime light exposure as a potentially valuable indicator of dementia risk that deserves further investigation.