Latest research: Sunbathing can prevent dementia! But too much or too little sun exposure can cause dementia!

The team led by Professor Yu Jintai from Huashan Hospital affiliated to Fudan University and the team led by Professor Tan Lan from Qingdao Municipal Hospital affiliated to Qingdao University conducted a study involving more than 360,000 people and with a nine-year follow-up, and found that proper sun exposure can help prevent Alzheimer's disease.

This study revealed for the first time the relationship between outdoor light exposure and dementia, providing a new approach to preventing dementia. The research results were published in the British Medical Council Internal Medicine on April 25.

"Light is one of the important factors that affect the circadian rhythm. Changes in light conditions send signals to the circadian structure in the brain through the visual pathway, thereby adjusting the rhythm of physiology and behavior. At the same time, light can also affect brain function through non-visual pathways."

Yu Jintai told reporters, "However, there has been no large-scale cohort study to reveal the relationship between light exposure time and the occurrence of dementia."

To find out this question, the joint team used the UK Biobank cohort, which included 362,094 non-demented participants aged 37 to 73 years, who were followed up for an average of 9 years. All participants reported the average length of outdoor light exposure per day in summer and winter.

The study found that during the 9-year follow-up, a total of 4,149 participants were diagnosed with new-onset dementia. There was a typical nonlinear "J-shaped" relationship between outdoor light exposure and dementia, that is, too short or too long outdoor light exposure would increase the risk of dementia.

"The optimal outdoor lighting duration is 2 hours a day in summer and 1 hour a day in winter, with an average of 1.5 hours a day," said Yu Jintai.

The study found that compared with people who received an average of 1.5 hours of outdoor light per day, the risk of dementia increased by 28.7% for every 0.5 hour reduction in outdoor light exposure, and the risk of dementia increased by 7.0% for every 0.5 hour increase in outdoor light exposure. Outdoor light exposure time shorter than the optimal outdoor light time increased the risk of dementia. This result was more significant in the elderly population around 60 years old.

"Outdoor light exposure may protect against dementia by affecting vitamin D levels in the body, as vitamin D is involved in multiple key pathways in brain health, including neuroprotection, regulation of immune responses, suppression of inflammation, and modulation of oxidative stress."

When talking about the mechanism of outdoor light and dementia, Tan Lan said, "Outdoor light also affects cognitive function by acting on the human body's internal clock, the optic chiasmatic nucleus, to regulate circadian rhythms."

Next, the researchers will conduct experiments to further clarify the potential link between outdoor light and dementia.