42 Minutes of Bright Daylight a Day Linked to 17% Lower Dementia Risk
People who got about 42 minutes of bright daylight a day were roughly 17% less likely to develop dementia over eight years, according to a study in General Psychiatry that tracked nearly 90,000 adults. A neurologist not involved in the work called the genetic finding fascinating.
An incredibly easy habit lowers dementia risk by about 17%, according to a study published in the journal General Psychiatry. The habit is getting around 42 minutes of bright daylight per day.
The finding matters because more than 6 million Americans live with dementia. That number is expected to double by 2060 as the population ages and conditions linked to cognitive decline, such as obesity, become more common.
What the researchers did
The team tracked the daylight exposure of nearly 90,000 participants who had no dementia at the start. Each person was monitored for one week.
The researchers then compared outcomes over eight years between those who stayed healthy and those who developed dementia. People who received around 42 minutes of bright daylight daily were about 17% less likely to develop the condition than people who got less.
The link held after the researchers accounted for diet, obesity, physical activity and heart health.
Why light may matter
The effect may come from the body's circadian rhythm. Light entering the eyes activates this internal clock, which maintains sleep-wake cycles, supports immune function and helps fight inflammation.
Better sleep also helps. During restorative sleep, the brain carries out cellular maintenance and clears metabolic waste, a step that lowers the chance of cognitive problems later in life.
"We are beginning to recognize that our brains and bodies are profoundly influenced by environmental signals, including light, that regulate fundamental biological processes," said David Perlmutter, a board-certified neurologist who was not involved in the study.
Perlmutter said natural light belongs in the conversation about dementia alongside stress management and social connection.
Stronger link with a gene variant
The study also found the connection was stronger in people with the APOE4 gene variant, which raises the risk of Alzheimer's disease. Perlmutter called that a "particularly fascinating finding."
"Our genes influence our susceptibility, but our daily choices and environmental exposures can profoundly influence how that susceptibility plays out," he added.
Separate research points the same way on a different health measure. Researchers in central Europe published a study earlier this year finding that consistent exposure to natural light led to "more stable blood glucose levels and an overall improvement" in the metabolic profile of all 13 volunteers.
Winter can make daylight hard to find. A light therapy lamp may mimic sunlight on the darkest days, although there is no research on whether such lamps can prevent dementia.
