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“阳光维生素”，晒太阳就可以补充！但要注意这几点
The Importance of the "Sunshine Vitamin" During the Dark Winter Months
多年前，科学家就发现晒太阳可以补充维生素D。当人体皮肤表层的7-脱氢胆固醇遇到阳光里的紫外线后，就会生成这种维生素。人体内源性维生素D约80%在皮肤表皮合成，仅20%从食物中摄取，所以维生素D也被称为"阳光维生素"。The Importance of the "Sunshine Vitamin" During the Dark Winter Months
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，当一位波兰医生带着患有佝偻病(或软骨头)的城市儿童去乡下避暑时，发现了阳光与骨骼健康之间的联系。事实上，维生素D除了有益骨骼健康外，还对心脏、新陈代谢和免疫系统健康有益。
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.
维生素D被血液吸收，并转化为活性形式(一种开环甾体激素)和储存形式(25-羟基维生素D)——其功能更像是一种激素而不是维生素。因此，充足的维生素D对健康有着重要影响。
Potential benefits associated with vitamin D include:
维生素D的潜在健康益处包括：
Aids in calcium absorption for maintaining strong bones and teeth
促进钙吸收，保持骨骼和牙齿强健
Helps support healthy heart and immune function
有益心脏健康和增强免疫功能
Facilitates healthy cell development
促进健康的细胞发育
值得注意的是，只有裸露的皮肤接受太阳光照射的时候才能产生维生素D。因此，冬天更需要多晒太阳，才能补充充足的维生素D。
晒太阳的时间需要多久?
冬春季，将面部和双上臂暴露于阳光下 10～30 分钟，夏季由于紫外线较强，裸露部位较多，接受太阳直射 5～10 分钟，每周 2～3 次就能让身体产生足够的维生素 D。绝大多数人每天在阳光下晒 10 至 20 分钟即可。
隔着玻璃晒太阳有效吗?
隔着玻璃晒太阳会大大降低效果，因为中波紫外线 UVB 的穿透性比较差。在家中隔着玻璃晒太阳几乎是无效的，因为中波紫外线的透过率会大幅度降低，从而影响人体合成维生素 D。晒太阳的最佳地点是户外，因各种原因必须在室内晒太阳，也一定要打开窗子，让阳光直接与皮肤接触。
"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."
美国营养品公司嘉康利医学事务主席杰米·麦克马纳斯称：“当阳光照射皮肤时，人体就会产生维生素D，自然界中含有维生素D的食物较少，而牛奶是美国人饮食中维生素D的主要来源。随着夏令时间结束，通过阳光吸收维生素D的机会减少。因此，人们应该补充维生素D摄入量，尤其是在冬季。”
来源：Shaklee Corporation，丁香园
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