Under 42 minutes of bright daylight linked to higher dementia risk

Researchers analyzed data from 87,577 adults who wore wrist devices measuring light exposure. Over a median follow-up of 8.1 years, 741 participants developed dementia. The study, published in General Psychiatry, examined whether daily daylight exposure was associated with that risk.

Bright daytime light makes the difference

People exposed to average daytime light levels above 1,000 lux, roughly equivalent to an overcast day outdoors, had a 16% lower risk of developing dementia. Spending longer periods in light of at least 5,000 lux was linked to further risk reductions. Nighttime light exposure showed no statistically significant association with dementia risk in this study.

The most striking finding: receiving less than 42 minutes of bright daylight daily was a stronger predictor of dementia than six other well-established dementia risk factors combined. The researchers highlight daytime light exposure as a potentially overlooked indicator of brain health and dementia risk.

Association, not proven cause

This study identifies an association, not a causal relationship. It has not been shown that more daylight directly prevents dementia. For example, people who already experience cognitive decline may naturally spend less time outdoors, which could partly explain the link. Corresponding author Hongliang Feng of Guangzhou Medical University says daytime light exposure deserves further investigation as a dementia risk indicator.

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