A study of 360,000 people found that getting enough sun a day has the lowest risk of dementia

*For medical professionals only, a study of 360,000 people followed for 9 years tells you the answer! According to the World Health Organization (WHO), one person is diagnosed with dementia every 3 seconds in the world [1]
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Dementia patients in China account for nearly 1/4 of the global number of dementia patients [2].
As the fifth leading cause of death in the world, Chinese dementia patients pose a huge mental and economic burden on individuals, families and society
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 Finding controllable risk factors and clear control methods is an important way to reduce the incidence of dementia early and delay the progression of dementia.
What is the relationship between sun exposure and the risk of dementia? Recently, the team of Professor Yu Jintai from the Department of Neurology, Huashan Hospital Affiliated to Fudan University, has reached the main conclusions and published the research results in the internationally renowned journal BMC Medicine
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 So, how did the research work? What's new? What are the guidelines for our daily life? "Medical Neurology Channel" specially invited Professor Yu Jintai from Huashan Hospital Affiliated to Fudan University to interpret it for everyone
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 360,000 people, followed up for 9 years, a large sample to find the dose-response relationship between the length of sunshine and the risk of dementia Light is one of the important factors affecting the circadian rhythm, and its changes send signals to the circadian structure in the brain through the visual pathway to adjust physiology and behavior The rhythm, meanwhile, can also affect brain function through non-visual pathways
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 In the past, light therapy has also seen good results in areas such as Alzheimer's disease, non-seasonal depression, and sleep disturbances, but in modern society, people are exposed to significantly less time outdoors, typically—exposure to bright light throughout the day.
under artificial lighting
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 At present, there is no large-scale cohort study to reveal the relationship between the duration of outdoor natural light and new-onset dementia.
In order to solve this scientific problem, Professor Yu Jintai's team carried out this research work
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 Using the UK Biobank cohort, the research team included 362,094 non-demented participants aged 37 to 73 who were recruited between 2006-2010 and followed for an average of 9 years
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All participants reported the average amount of time they received outdoor light per day in summer and winter
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During follow-up, a total of 4149 participants were diagnosed with new-onset dementia
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 The best time is an average of 1.
5 hours per day, which is too high or too low! The research team conducted an in-depth study of the linear and non-linear relationship between outdoor light duration and dementia risk
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 The results showed that there was a typical nonlinear "J-shaped" relationship between the length of outdoor light and the risk of dementia.
Too short or too long outdoor light time would increase the risk of dementia
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The optimal outdoor light duration is 2 hours per day in summer and 1 hour per day in winter, with an average of 1.
5 hours per day (Figure 1)
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Figure 1: A "J-shaped" relationship between outdoor light duration and dementia risk Specifically, a 0.
5-hour decrease in outdoor light duration was associated with a 28.
7% increase in dementia risk compared with a population that received an average of 1.
5 hours of outdoor light per day.
For every 0.
5 hour increase in duration, the risk of dementia increased by 7.
0%
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 In addition, subgroup analysis by age showed that the "J-shaped" relationship was more pronounced in the elderly population older than 60 years, compared with the elderly who received an average of 1.
5 hours of outdoor light per day, the length of outdoor light in the elderly per day A reduction of 0.
5 hours was associated with a 30.
4% increase in dementia risk, and every 0.
5 hour increase in outdoor light hours was associated with a 6.
3% increase in dementia risk
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 Figure 2: 1.
5 hours of outdoor light per day may help prevent dementia In summary, this study shows that the length of outdoor light exposure can significantly affect the risk of dementia, and clear and specific outdoor light guidance will effectively prevent the occurrence of dementia
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 It is worth mentioning that most of the previous research on lighting and dementia has focused on artificial lighting at night, and this study highlights the importance of getting the optimal amount of natural light exposure to prevent or delay the onset of dementia
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 Talking to the authors This study is the first to demonstrate a "J-shaped" association between sun exposure and dementia risk, and providing detailed guidance on sun exposure can be effective in preventing dementia
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In addition, there are some very interesting findings.
In order to better understand these issues, we are honored to invite Professor Yu Jintai, the corresponding author of the study, from the Department of Neurology, Huashan Hospital Affiliated to Fudan University, to further analyze the relationship between sunlight exposure and dementia risk reduction.
some key factors associated with it
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 What are the possible reasons for the 'J-shaped' association between sun exposure and dementia risk in the medical community? Professor Yu Jintai is well aware of the dangers of not basking in the sun, such as affecting mood, sleep and other factors closely related to dementia
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But why does too much sun exposure increase dementia risk? In fact, the nonlinear relationship between sun exposure and disease risk does not only exist in dementia
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In a previous study of solar radiation (sunlight) and temperature exposure and risk of stroke in a cohort of 16,606 participants, when researchers divided light intensity into tertiles, the results showed that compared with higher or higher With lower sun exposure, the risk of stroke was lowest in the second group
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We believe that this "J-shaped" relationship may be related to the effect of light on the core temperature of the human body
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In the upright state, direct exposure of the human head to solar radiation may cause brain temperature to exceed core temperature, as broad-spectrum light penetrates into the skin and heats the subcutaneous tissue
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The inverted U-shaped relationship between photothermal therapy and cognitive performance also supports the claim that prolonged exposure of the head and neck to sunlight increases core temperature, which leads to cognitive decline
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 In the medical community in general, the current life/work model, which makes most modern people stay indoors during the day, does not help us develop the habit of regular sun exposure to reduce the risk of dementia.
What other ways can we make up for it? Professor Yu Jintai's many benefits of sunlight are currently irreplaceable such as indoor lighting
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For example, sunlight can stimulate the body to release nitric oxide, and nitric oxide has the effect of lowering blood pressure and maintaining vascular tone, which is beneficial for maintaining cardiovascular health
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In addition, about 50% to 90% of the vitamin D in the human body needs to be synthesized and absorbed by sunlight
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Persistent vitamin D deficiency can be associated with nearly every chronic disease you can think of, including metabolic abnormalities (such as osteoporosis), cardiovascular disease, cancer, diabetes, autoimmune disease, mental illness, and more
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Sunbathing is the easiest and freest way, while improving sleep, supplementing vitamin D, and more
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Therefore, it is recommended that you work as close as possible to the windows that can receive sunlight, and go out during noon breaks and weekend breaks to ensure the best average daily light amount and maintain a balanced sun exposure
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Of course, regular exercise and adequate and high-quality sleep are also very important to good health
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Expert Profile Professor Yu Jintai, Chief Physician, Doctoral Supervisor, Young Changjiang Scholar of the Ministry of Education Executive Deputy Director of the Neurology Institute of Fudan University Committee Member, Deputy Head of Neuropsychology and Behavior Group of Neurology Branch of Chinese Medical Association, Deputy Chief Editor of Brain Disorders Magazine, and Deputy Chief Editor of Ann Transl Med Magazine
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He presided over a number of general and major projects of the National Natural Science Foundation of China, led the formulation of international guidelines for evidence-based prevention of Alzheimer's disease, and published many academic papers in top journals such as Lancet Neurology and Alzheimers Dement
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He is good at clinical diagnosis and treatment of memory loss, brain atrophy, unsteady walking, various dementias and Parkinson's syndrome
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Reference source: [1] Maria Cohut, Fact checked by Jasmin Collier.
Dementia: 10-year risk estimates may inform prevention.
Medical News Today.
5 September 2018.
Available at: https:// .
php Last assessed on 2018-09-09.
[2]GBD 2016 Dementia Collaborators.
Global,regional,and national burden of Alzheimer's disease and other dementias,1990-2016:a systematic analysis for the Global Burden of Disease Study 2016.
The Lancet.
Neurology.
2019;18(1):88-106.
[3]LingZhi Ma, YaHui Ma , YaNan Ou et al.
Time spent in outdoor light is associated with the risk of dementia: a prospective cohort study of 362094 participants[ J].
BMC Medicine (2022) 20:132.
https://doi.
org/10.
1186/s12916-022-02331-2 First release of the text: Neurology Channel of the Medical Community Editor-in-charge of Huashan Hospital Affiliated to the University: Mr.
Lu Li in the medical community strives to be accurate and reliable when the published content is approved, but does not make any claims about the timeliness of the published content and the accuracy and completeness of the cited materials (if any).
promises and warranties, and does not assume any responsibility for the outdated content, possible inaccuracy or incompleteness of the cited information, etc.

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Relevant parties are requested to check separately when adopting or using it as a basis for decision-making
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