多年前，科學(xué)家就發(fā)現(xiàn)曬太陽可以補(bǔ)充維生素D。當(dāng)人體皮膚表層的7-脫氫膽固醇遇到陽光里的紫外線后，就會(huì)生成這種維生素。人體內(nèi)源性維生素D約80%在皮膚表皮合成，僅20%從食物中攝取，所以維生素D也被稱為"陽光維生素"。

The connection between sunlight and bone health was made over 200 years ago when a Polish doctor treated inner city children with rickets (or soft bones) by taking them to the countryside for the summer months. In fact, vitamin D promotes heart, metabolic, and immune system health in addition to supporting bone health.
200多年前，當(dāng)一位波蘭醫(yī)生帶著患有佝僂?。ɑ蜍浌穷^）的城市兒童去鄉(xiāng)下避暑時(shí)，發(fā)現(xiàn)了陽光與骨骼健康之間的聯(lián)系。事實(shí)上，維生素D除了有益骨骼健康外，還對(duì)心臟、新陳代謝和免疫系統(tǒng)健康有益。

Vitamin D is absorbed into our bloodstream and converted to the active form (a secosteroidal hormone) and a storage form (25-hydroxyvitamin D) – it functions more like a hormone than a vitamin. So, it is no surprise that having sufficient levels of vitamin D is so important for a broad array of health effects.
維生素D被血液吸收，并轉(zhuǎn)化為活性形式（一種開環(huán)甾體激素）和儲(chǔ)存形式（25-羥基維生素D）——其功能更像是一種激素而不是維生素。因此，充足的維生素D對(duì)健康有著重要影響。

Potential benefits associated with vitamin D include:
維生素D的潛在健康益處包括：
Aids in calcium absorption for maintaining strong bones and teeth
促進(jìn)鈣吸收，保持骨骼和牙齒強(qiáng)健
Helps support healthy heart and immune function
有益心臟健康和增強(qiáng)免疫功能
Facilitates healthy cell development
促進(jìn)健康的細(xì)胞發(fā)育

值得注意的是，只有裸露的皮膚接受太陽光照射的時(shí)候才能產(chǎn)生維生素D。因此，冬天更需要多曬太陽，才能補(bǔ)充充足的維生素D。

曬太陽的時(shí)間需要多久？

冬春季，將面部和雙上臂暴露于陽光下 10～30 分鐘，夏季由于紫外線較強(qiáng)，裸露部位較多，接受太陽直射 5～10 分鐘，每周 2～3 次就能讓身體產(chǎn)生足夠的維生素 D。絕大多數(shù)人每天在陽光下曬 10 至 20 分鐘即可。

隔著玻璃曬太陽有效嗎？

隔著玻璃曬太陽會(huì)大大降低效果，因?yàn)橹胁ㄗ贤饩€ UVB 的穿透性比較差。在家中隔著玻璃曬太陽幾乎是無效的，因?yàn)橹胁ㄗ贤饩€的透過率會(huì)大幅度降低，從而影響人體合成維生素 D。曬太陽的最佳地點(diǎn)是戶外，因各種原因必須在室內(nèi)曬太陽，也一定要打開窗子，讓陽光直接與皮膚接觸。

"Vitamin D is produced when sunlight touches our skin, and very few foods in nature contain vitamin D, with fortified foods – primarily cow's milk – being responsible for most of the vitamin D in the American diet," said Jamie McManus, Shaklee's Chair of Medical Affairs. "As daylight savings time ends, we have less opportunity to absorb vitamin D through sunlight. Therefore, people should supplement their vitamin D intake, especially during winter."
美國營養(yǎng)品公司嘉康利醫(yī)學(xué)事務(wù)主席杰米·麥克馬納斯稱：“當(dāng)陽光照射皮膚時(shí)，人體就會(huì)產(chǎn)生維生素D，自然界中含有維生素D的食物較少，而牛奶是美國人飲食中維生素D的主要來源。隨著夏令時(shí)間結(jié)束，通過陽光吸收維生素D的機(jī)會(huì)減少。因此，人們應(yīng)該補(bǔ)充維生素D攝入量，尤其是在冬季。”

來源：Shaklee Corporation，丁香園
編輯：董靜