When summer arrives, many people are armed with sunscreen, sun-protective clothing, sun-protective masks, sunhats, and parasols, for fear of being exposed to the sun. As everyone knows, excessive sun protection is not good for physical health, and moderate sun exposure has many benefits for the human body. In this article, let's take a look at the importance of sun exposure.
Sunlight and vitamin D
Vitamin D is a fat-soluble vitamin that is essential for the human body. Everyone knows that vitamin D can promote calcium absorption, and vitamin D deficiency or insufficiency will cause calcium deficiency, osteoporosis, and even rickets, osteomalacia, etc. But this is only one of the many physiological functions of vitamin D, in addition to the fact that vitamin D also has a variety of functions such as regulating hormone secretion, regulating immune function, and regulating cell proliferation and differentiation. Vitamin D deficiency may increase the risk of obesity, diabetes, high blood pressure, cancer, psoriasis, and several autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, systemic sclerosis, etc.).
A large number of studies have found that vitamin D deficiency is widespread, and about 1 billion people in the world are vitamin D deficient or insufficient, and high-risk groups include newborns, infants, pregnant women, and the elderly. The vitamin D nutritional status was significantly distributed in the north of 35°N, the vitamin D deficiency was better in the south of 25°N, and the central region was in the middle. In addition, the season also has a greater impact on vitamin D nutrition, and the vitamin D nutrition level in summer and autumn in northern China is better than that in winter and spring.
Why are there such regional and seasonal differences? The reason for this is that sunlight is a key factor in the synthesis of vitamin D in the body. The source of vitamin D in the human body is diet and the body's own synthesis. The content of vitamin D in food is less, and more than 90% of vitamin D is synthesized by the body itself. Our epidermis and dermal tissues contain 7-dehydrocholesterol, which can be converted into vitamin D when exposed to sunlight or ultraviolet light. Therefore, it is very important for our health to spend more time in the sun and allow the body to synthesize more vitamin D.
It is mainly UVB rays in ultraviolet rays that promote the synthesis of vitamin D in our body, not UVA, and 10 a.m. to 3 p.m. is the time when UVB levels are highest in ultraviolet rays. So, the best time to synthesize vitamin D from sun exposure is between 10 a.m. and 3 p.m. Of course, in order to avoid skin problems caused by excessive UV exposure, the time of each sun exposure should be relatively short, 15-30 minutes. Literature shows that in the summer with a good climate and abundant sunshine, healthy adults can achieve adequate and safe levels of vitamin D in the human body by wearing only swimsuits, or basking their hands and legs in the sun for 5-30 minutes twice a week, from 10 a.m. to 3 p.m. Darker skin will need to tan longer than lighter skin to reach the same level. Of course, the data is only for your reference, to understand the effectiveness of sun exposure to synthetic vitamin D, it is not recommended that you wear swimwear and expose to the sun.
Sunlight and serotonin
Serotonin, or serotonin, is widely found in mammalian tissues as a neurotransmitter and a vasoactive substance that plays a variety of important physiological roles in the central nervous system and surrounding tissues. Studies have shown that serotonin is widely involved in the regulation of various mental activities, and is related to anxiety disorders, obsessive-compulsive disorder, autism, affective disorders, schizophrenia, alcohol, and drug dependence. Serotonin is a "happy hormone" that produces happiness and well-being, which regulates a person's mood. Several studies have found a strong relationship between sunlight and the release of serotonin.
In the 20s of the last century, the German medical scientist Emil found that people in Nordic countries are prone to depression syndrome, with insomnia, headaches, weight gain, irritability, depression, anxiety, fatigue and other symptoms. Further research led to the conclusion that this phenomenon was related to the relatively short hours of daylight exposure in the region. Sunlight stimulates the brain to secrete serotonin, which regulates the communication activities between neurons in the human brain, making people feel refreshed. There is also information that people living near the equator rarely experience depression.
Researchers in Australia measured serotonin concentrations in the cerebral blood vessels of 101 healthy men aged 18-79 and found that serotonin metabolite concentrations were related to climatic conditions and seasons. On those days when the light is strong, the value of serotonin conversion is higher than that of dark weather, and the turnover of serotonin in the brain is lowest in winter. This confirms that the rate at which the brain produces serotonin is directly related to the effective time of sun exposure.
Psychological studies have also found that exercising in the sun for more than half an hour a day significantly improves sleep and mood. Because sunlight acts as a natural "stimulant", it can promote the secretion of serotonin in the brain.
Sunlight and melatonin
Melatonin, a hormone produced by the pineal gland located in our brain, can regulate the biological clock, induce sleep, regulate the endocrine system, delay aging, enhance immunity, etc. The pineal gland is an oval-shaped gland in our brain, known as the pineal gland because it resembles a pineal cone. The activity of the pineal gland shows obvious rhythm, and the synthesis and secretion of melatonin also show circadian rhythm, monthly rhythm, seasonal rhythm, and life rhythm.
Among them, circadian rhythm and seasonal rhythm are closely related to light. When it is dark, the retina perceives weaker light, which sends a signal to increase the synthesis and secretion of melatonin by the pineal gland; During the day, when the retina receives more light, the pineal gland synthesizes and secretes less melatonin. Due to the seasonal changes in light time and intensity, melatonin secretion takes longer and secretes more in winter when the days are short and the nights are long. In summer, when the days are long and the nights are short, the melatonin secretion time is short and the secretion is small. This is one of the reasons why it is more difficult to get out of bed in winter than in summer.
Melatonin, whose chemical name is 5-methoxy-N-acetyltryptamine, is made by the conversion of serotonin, or serotonin, by enzymes. It can be said that serotonin is the precursor of melatonin, and if the secretion of serotonin is insufficient during the day, it will also affect the secretion of melatonin at night. Serotonin is secreted more during the day and less at night; Melatonin is secreted less during the day and more at night. Serotonin is made at sunrise and melatonin is produced at sunset.
During the day, sufficient serotonin can make us energetic and devote ourselves to work and study; At night, serotonin is converted into melatonin, which helps us feel drowsy and fall asleep. Insufficient daytime sunshine will cause insufficient serotonin secretion and increased melatonin secretion, making people feel bad mood and drowsiness; At the same time, insufficient serotonin secretion will further affect the secretion of melatonin at night, thus affecting sleep.
Insisting on 15-30 minutes of activity in the sun every day can not only help the body synthesize vitamin D, but also help the body's serotonin secretion, make people feel happy, and at the same time reduce the secretion of melatonin during the day, reduce drowsiness, increase the secretion of melatonin at night, and improve sleep. Of course, the benefits of moderate sun exposure go far beyond that. With so many benefits, don't you get sunburned?
Finally, I would like to remind everyone that although sun exposure is good, it should not be overexposed, otherwise it may lead to sunburn, tanning, skin aging, and even induce skin cancer. Excessive sun protection and excessive sun exposure are harmful to human health and are not advisable.
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