Daily sunlight may lower dementia risk by up to 25%

A new study has found that spending an appropriate amount of time in natural sunlight every day may reduce the risk of dementia by as much as 25%. Researchers say that a lifestyle involving prolonged exposure to dim indoor environments may significantly increase the risk of developing dementia, a condition that affects memory and cognitive function.

The study conducted in China examined the relationship between the amount of time people spend in daylight and their risk of developing dementia. Researchers from several Chinese universities followed approximately 87,600 participants over a period of eight years.

The average age of the participants was 62 years and each wore an actigraphy device on their wrist. These devices recorded their daily physical activity as well as their exposure to sunlight throughout the day.

An actigraphy device includes a built-in light sensor to measure light intensity and an accelerometer which detects movement and changes in speed or direction such as how quickly a person accelerates, slows down or changes course.

During the study, 741 participants were diagnosed with dementia. The findings showed that individuals who spent most of their time indoors in dimly lit environments had a higher risk of developing dementia. However, when these individuals began spending more time in brighter environments, their risk decreased by 15% to 25%.

The researchers also found that exposure to an average of 1,000 lux or more during the daytime roughly equivalent to a moderately bright room or an overcast outdoor day was associated with a 16% lower risk of dementia compared with people who remained in dim light.

Spending approximately 90 minutes a day in light with an intensity of 3,000 lux or more comparable to natural outdoor daylight was linked to an 18% reduction in dementia risk. Similarly, spending 40 to 45 minutes daily in very bright light of 7,000 lux or higher was associated with a 17% lower risk of developing dementia.

The study also found that receiving less than 0.7 hours (about 42 minutes) of bright natural daylight each day was a stronger predictor of dementia than several well-known risk factors including obesity, alcohol consumption and traumatic brain injury.

The protective effect of daylight was even more pronounced in people who were exposed to higher levels of light at night as nighttime light can disrupt sleep. Poor or disturbed sleep has long been linked to an increased risk of dementia.

According to the study, which was published in the medical journal General Psychiatry, people who were exposed to a lot of light at night still experienced a 30% to 38% lower risk of dementia if they received sufficient bright daylight during the day.

Likewise, individuals who tend to stay awake late at night had up to a 40% lower risk of dementia if they spent more time in natural sunlight during the daytime.

While the findings suggest a strong association between daylight exposure and a lower risk of dementia, they do not prove that sunlight alone prevents the disease. However, the research indicates that maintaining regular exposure to natural daylight may be an important part of supporting long-term brain health.