Sunbathing is a "technical job". It is good for your health and does not make you look old.

In early spring in March, everything comes back to life. New buds appear on the branches, and everything is full of vitality. We should also follow the laws of nature and go out to get more sun. Sunbathing can help the skin synthesize vitamin D, which in turn promotes calcium absorption and prevents osteoporosis. However, long-term sun exposure will cause skin aging. How should we choose between the two dilemmas? Dr. Huang from the Department of Endocrinology of Zhongda Hospital Affiliated to Southeast University pointed out that sunbathing is a "technical job" and it is important to learn the method.

Ultraviolet rays: the body loves it but also fears it

The main source of ultraviolet light in nature is the sun, and the body has a love-hate relationship with it. Dr. Huang said that before sunbathing, you should first understand the sun. The ultraviolet rays in the sun are divided into UVA, UVB, and UVC according to their wavelengths. Among them, UVC cannot reach the surface of the earth, and the skin can only be exposed to UVA and UVB.

UVA refers to long-wave ultraviolet rays, which account for 90% to 95% and can reach the dermis of the skin. When the skin is exposed to long-wave ultraviolet rays (UVA), it will cause tanning, dry skin, loss of elasticity, and wrinkles. Long-wave ultraviolet rays can penetrate clouds, glass, and clothes, so they can also be exposed indoors and on cloudy days, but long-wave ultraviolet rays cannot help the skin synthesize vitamin D.

UVB refers to medium-wave ultraviolet rays, which account for 5% to 10% and can only reach the epidermis of the skin, but its energy is relatively high. Exposure to medium-wave ultraviolet rays (UVB) can cause skin redness and sunburn, and can act on the skin to help synthesize vitamin D. However, ordinary glass can block UVB, so sunbathing through glass is ineffective.

Sunbathing, the effect is better if the method is correct

Dr. Huang introduced that latitude, altitude, air pollution, and time of day outside will affect the effect of sun exposure. To improve the effect of sun exposure, it is recommended to go out appropriately when the UV index is ≥3 and get more sun exposure, but it should be noted that you should not sunbathe through glass. Generally speaking, 11:00-15:00 in spring, summer, and autumn is the best time for sun exposure. At this time, expose the face and upper arms to the sun for 5 to 30 minutes (depending on many factors), and the effect will be better 3 times a week. It should be noted that it is not recommended to evaluate the synthesis of vitamin D based on whether the skin is tanned when sunbathing, because skin tanning is the effect of UVA. In addition, it is not advisable to expose directly to the sun when the sun is the strongest to avoid inducing skin cancer.

Sunscreen, have you chosen the right one?

Many people worry about tanning and skin aging when they are sunbathing. Sun protection is an important measure to prevent pigmentation and photoaging, but people are also worried that applying sunscreen will affect the synthesis of vitamin D in the skin and thus affect the absorption of calcium? Dr. Huang pointed out that the sun protection index of sunscreen includes PA and SPF. PA represents the ability to resist UVA, preventing tanning and aging. SPF represents the ability to resist UVB, preventing redness and sunburn, but also hinders the synthesis of vitamin D. Therefore, it is recommended to choose sunscreen products with high PA and low SPF. People who already have vitamin D deficiency can appropriately reduce the areas and probability of using sunscreen.

These factors can affect the synthesis of vitamin D

Sunlight can help the body synthesize vitamin D, promote the body's absorption and utilization of calcium and phosphorus, and is beneficial to bone health. Most of the vitamin D needed by the human body comes from sun exposure, and a small part comes from food. Age is also an important factor affecting the synthesis of vitamin D. Aging skin produces less vitamin D than young skin, and aging kidneys also affect the further activation and function of vitamin D in the body. In addition, smoking, obesity, skin color, genetic factors, and long-term use of drugs (phenytoin, phenobarbital, rifampicin, etc.) can also affect vitamin D levels.

At present, more and more young people spend less time outside and less sun exposure due to lifestyle and other reasons. Vitamin D deficiency has become one of the global public health issues. In Asia, about 75% of the population is vitamin D deficient or insufficient. Therefore, it is important to get enough sun exposure regularly and scientifically. In addition, if you want to know whether you have vitamin D deficiency, you can go to a regular hospital for a blood test for 25OHD. For vitamin D deficiency, you can take oral vitamin D preparations under the guidance of a doctor if necessary to improve it.