You are probably exposed to sunlight on a daily basis and know of its health effects. But you may not know that too much or too little sunlight holds no health benefit.
For example, a recent study found that sunlight helps prevent dementia—but only when exposure is moderate. Why is that? And how much is “moderate”?
Exposure to Sunlight Prevents Dementia
Recently, Professor Jintai Yu’s team from Fudan University in China, together with Professor Lan Tan’s team from Qingdao University, conducted a study that included more than 360,000 people with up to nine years of follow-up.The research concluded that average daily exposure to 1.5 hours of sunlight could prevent dementia, but too much or too little sunlight was harmful to health. The study discovered for the first time the relationship between hours of outdoor light exposure and dementia and provided a new idea for dementia prevention. The study was published in BMC Medicine on April 25, 2022.
The joint team used the UK Biobank cohort to include 362,094 non-demented participants between the ages of 37 and 73, and they had been followed up for an average of nine years. All participants were required to report the average number of hours of outdoor sunlight received per day in the summer and winter seasons.
A total of 4,149 participants were diagnosed with new-onset dementia during the nine-year follow-up period. There was a typical nonlinear “J-shaped” relationship between hours of outdoor sunlight exposure and dementia onset. In a word, too little or too much outdoor sunlight increased the risk of dementia.
The study found that the risk of dementia increased by 28.7 percent for every 0.5-hour reduction in outdoor sunlight exposure and 7.0 percent for every 0.5-hour increase compared to those who received an average of 1.5 hours of outdoor sunlight exposure per day. This result was even more prominent in the over-60 age group.
Reduced sunlight exposure was more likely to lead to dementia than increased sunlight exposure.
Why Exposure to Sunlight Can Prevent Dementia
Regarding the mechanism of outdoor sunlight exposure and the pathogenesis of dementia, the authors found that outdoor sunlight could prevent dementia by affecting the vitamin D level in the body. In the brain, vitamin D is involved in several key pathways, including neuroprotection, regulation of the immune response, suppression of inflammation, and regulation of oxidative stress. Exposure to sunlight facilitates the body’s synthesis of vitamin D, which can play a key role in the prevention of dementia.In the toxicity field, dosage determines whether a substance is toxic or not. The same is true for sun exposure: more or less can all be associated with dementia.
Only Exposure to Moderate Sunlight Is Beneficial
Sunlight is as much a gift from nature as air and water, and sunbathing has become a way of life for people. Over time, the sea, beaches, and sunbathing have become standard leisure activities. Excessive sunlight exposure poses many risks to human health, including sunburn, skin cancer, and eye disease. In an upright position, your head is directly exposed to solar radiation, raising brain temperatures to or even above core temperature, while broad-spectrum light can penetrate millimeters into the skin and heat underlying tissues, again leading to cognitive decline.Whether it’s summer or winter, you should get outside in moderate amounts of sunlight to prevent dementia. However, in this regard, it is better to prevent heat stroke before sun exposure to prevent dementia.
How to Expose Yourself to Sunshine Correctly
Choose the right time of day. Two times of day are the best for exposure to sunlight. You can choose before 11 a.m. when the sun emits infrared rays, and you will feel warm and soft when exposed to the sun. You can also choose 3:00 to 4:00 p.m. when the sun emits beneficial ultraviolet rays, and you will feel comfortable when exposed to the sun.Choose the appropriate clothing. It is better to wear red clothing when in contact with the sun; the second best choice is white, but avoid black. The red and white clothing can block the killing power of shortwave ultraviolet light, leaving the infrared sunshine beneficial for the human body, while also not heating up too much.
Sunbathing through glass is not ideal. If you really don’t want to go outside, you can also choose to open the window and expose your body to direct sunlight. Sunbathing through glass may not help your body to synthesize vitamin D.
Protection from sunlight damage. In summer, if you are at the beach and other sunny places you need to apply skin cream to avoid sunburn. Sunbathing your hands, feet, and legs can be a good way to get rid of the cold in your joints and legs and speed up the absorption of calcium in your body. You can also pick your favorite sunglasses to protect your eyes from UV rays in bright sunlight, and don’t read books, cell phones, etc. under bright sunlight. Additionally, you might choose a hat that you like in a light color, which can help to shield the top of your head from sunburn. In order to prevent heat stroke, stay hydrated and pay attention to how much water you are drinking.
Other Benefits of Sunlight Besides Preventing Dementia
Outdoor light can also affect the “body clock,” which influences the conversion of serotonin to melatonin. Melatonin is a hormone produced by the pineal gland of the brain. Under normal conditions, serotonin is produced more during the day and less at night, while melatonin is produced less during the day and more at night. Moderate daytime exposure to sunlight helps the secretion of serotonin, which makes people happy, and also reduces the secretion of melatonin during the day, which reduces sleepiness, and increases the secretion of melatonin at night which can improve sleep. Therefore, moderate daytime exposure to sunlight may also reduce the occurrence of dementia.Sunlight contains red and near-infrared light, which act as stimulants for the mitochondria and can stimulate them to synthesize more ATP which makes you more energetic. Near-infrared light can also increase the production of melatonin in the mitochondria, which can help you clear your cells of many substances that affect your mood and make you feel happier.
In addition, outdoor UV exposure has been reported to inhibit the formation of atherosclerotic plaques in mice; whether it has a similar effect in humans should require more research evidence to support it. Even on cloudy days, there is always more sunshine outside, and you can go out for more walks.
Exposure to sunlight also promotes the absorption of calcium in the body. Calcium is one of the essential nutrients for the human body. Of course, there is no calcium in sunlight, and you still need to take it in from food or medicine if you want to supplement calcium. However, sunlight can stimulate the human skin, which in turn converts 7-dehydrocholesterol into vitamin D3, which can be absorbed into the bloodstream and metabolized to form active vitamin D. Vitamin D can effectively promote the intestinal tract. It can effectively promote the absorption of calcium in the intestines, kidneys, and other organs as well, so that the intake of calcium elements can be maximized.
If you don’t have enough calcium in your body, it is difficult to get calcium even if you are exposed to a lot of sunlight. While consuming calcium-rich foods, you can get proper exposure to sunlight to promote absorption. To put it bluntly, sunlight does not replenish calcium, but it can promote calcium absorption.
