[Sportschosun Reporter Jang Jong-ho] A large-scale study has found that getting enough sunlight during the day may help lower the risk of developing dementia.
Researchers from Guangzhou Medical University and the medical school of Hong Kong Chinese University recently published the results in the international journal General Psychiatry. They followed about 87,600 adults with an average age of 62 for roughly eight years.
The researchers asked participants to wear an actigraphy device on their wrists. The device was equipped with a light sensor to measure exposure and an accelerometer to record body movement, allowing the team to analyze participants' daily light exposure and activity patterns.
The analysis showed that people who spent a lot of time in dark indoor environments faced a higher risk of dementia. However, exposure to brighter environments was associated with a 15% to 25% reduction in risk.
Specifically, people exposed to an average of at least 1,000 lux of light during the day had a 16% lower risk of dementia than those who lived in relatively dim environments. A level of 1,000 lux is comparable to bright indoor lighting or the brightness outdoors on a cloudy day.
Those exposed to bright light of at least 3,000 lux for about 1 hour and 30 minutes a day saw an 18% reduction in dementia risk. A level of 3,000 lux is similar to the brightness of a typical outdoor environment.
Even exposure to very bright light of 7,000 lux or more for about 40 to 45 minutes a day was linked to a 17% lower risk.
The researchers said that when daily exposure to bright light was less than 42 minutes, or 0.7 hours, it emerged as a stronger predictor than six major dementia risk factors, including obesity, alcohol consumption and traumatic brain injury.
The benefits of bright light during the day were even more pronounced among people who were heavily exposed to artificial light at night.
Nighttime light exposure can disrupt sleep, and insufficient sleep and poor sleep quality are known to be associated with a higher risk of dementia.
But according to the study, even people who were exposed to a lot of light at night could reduce their dementia risk by 30% to 38% if they received enough bright light during the day. Even people with nocturnal habits, often called "night owls," saw their dementia risk fall by about 40% when daytime light exposure was high. The analysis also found that among people with genetic factors that raise the risk of Alzheimer's disease (AD), increased daytime light exposure was associated with a 19% to 27% reduction in dementia risk.
The researchers explained that light is one of the most important signals regulating the body's internal clock, or circadian rhythm.
The circadian rhythm affects not only sleep-wake cycles but also cognitive function. When the body's clock is disrupted, the risk of neurodegenerative diseases, including dementia, may rise.
The researchers said, "Sufficient exposure to light during the day may have helped reduce dementia risk by stabilizing the circadian rhythm and improving the quality of sleep at night." They also noted that past brain-imaging studies found atrophy in specific brain regions in dementia patients, and early findings suggest that enough daytime light exposure may help slow that brain shrinkage.
However, the researchers emphasized that the study only showed an association between light exposure and dementia risk, not a direct causal relationship, and said further research is needed.
Jang Jong-ho, bellho@sportschosun.com
