小顾营养博客

背景知识：

维生素D的DRIs
中国营养学会18岁以上成人维生素D的RNI是5mg，18岁以下儿童一般为10mg。

维生素D的作用
它是钙磷代谢的最重要调节因子之一，可由维生素D原(pro–vitamin D)经紫外线(270～300)nm激活形成，活性维生素D[1，25一(OH)2D3]能通过促进钙结合蛋白(Ca–binding protein)合成而对钙吸收起重要作用。

维生素D的毒性
维生素D是脂溶性，比较不容易从体内排出。婴儿最容易发生维生素D中毒，已有报道每151摄入50μg维生素D可引起高维生素D血症。由于过量摄入维生素D有潜在的毒性，中国营养学会建议维生素D的IU值为20μg／d。

日晒产生维生素D的机制
动物皮下7脱氢胆固醇、酵母细胞中的麦角固醇都是维生素D原，经紫外线激活分别转化为维生素D3 (cholecalciferol)及维生素D3(ergocalciferol)。人和许多动物的皮肤和脂肪中都含7脱氢胆固醇，故皮肤经紫外线照射后，即可产生维生素D3，然后被运往肝、肾，转化为具有生理活性的形式后再发挥其生理作用。

富含维生素D的食物
含维生素D较丰富的食物有动物肝脏、鱼肝油、禽蛋类等。奶类也含有少量的维生素D，每100g奶含量在1mg以下。故以奶为主食的6岁以下儿童，补充适量的鱼肝油，对其生长发育有利。

 

July 16, 2009 — The American Academy of Dermatology (AAD) has issued an updated position statement on vitamin D after reviewing more recent evidence regarding the role of vitamin D in maintaining optimal health. The National Council on Skin Care Prevention also released its own position statement on July 14.

2009年7月16日美国皮肤科医学会(AAD)在回顾了维生素D在保持理想健康方面发挥作用方面最近的证据后，发布了关于维生素D作用的最新说明。

Individuals who regularly and properly practice sun protection may be at risk for vitamin D insufficiency and may require a higher dose of vitamin D, either from dietary sources or from supplements. Because of skin cancer risk from ultraviolet (UV) radiation, AAD does not recommend unprotected exposure to radiation from the sun or from indoor tanning devices.

那些定期适当锻炼并防晒的人也可能有维生素D不足的危险，他们可能也需要从食物或者补充剂中获取更高水平的维生素D。考虑到紫外线导致皮肤癌的危险，美国皮肤科医学会并不推荐暴露于阳光辐射或使用室内晒黑装置。

"The vitamin D position statement supports the Academy's long-held conviction on safe ways to get this important vitamin — through a healthy diet which incorporates foods naturally rich in vitamin D, vitamin D-fortified foods and beverages, and vitamin D supplements," dermatologist and AAD president David M. Pariser, MD, FAAD, said in a news release.

皮肤科医生、美国皮肤科学会主席David M. Pariser在一个新闻发布会上说：有关维生素D作用的说明支持了学会长期以来所坚持的原则，即应通过安全的方式来获取这种重要的维生素。比如采用富含维生素D天然食物、强化维生素D的食物和饮料以及维生素D营养补充剂这类健康的饮食。
　
"The updated recommendation for individuals who practice daily sun protection acknowledges that while protecting the skin from the damaging rays of the sun is important, so is maintaining adequate vitamin D levels," Dr. Pariser said. "Concern about vitamin D should not lead people to forego sun protection, but rather prompt a conversation with their physician about how to ensure adequate and safe vitamin D intake while guarding against skin cancer."

Pariser医生提到，为那些天天锻炼并注重防晒的人所提供的最新指南中承认，保护皮肤免受日光中射线的伤害是非常重要的，所以应当保持充足的维生素D水平。关注维生素D的同时不应该使人们放弃防晒，而是向医生了解怎样能够在安全防范皮肤癌的同时确保安全充足的维生素D摄入。
　
In addition to individuals who protect themselves from sun or other UV exposure by daily use of sunscreen on exposed skin or by wearing sun-protective clothing, others at risk for vitamin D insufficiency include elderly individuals or those who have dark skin, photosensitivity, obesity, or fat malabsorption. These at-risk individuals should consult their physician regarding options for ensuring adequate vitamin D levels through dietary intake or supplement use, and physicians should be equipped to advise them properly.

对个人来说除了平时在暴露的皮肤上涂抹防晒乳或者穿着可以防紫外线的衣服来保护自己免受阳光或者其他紫外线的照射外，其他具有高维生素D摄入不足风险的人，比如老年人、深色皮肤、光敏、肥胖、脂肪吸收障碍的人，这些高危个体应该向他们的医生咨询如何选用饮食或者营养补充剂来确保摄入足够的维生素D水平，并且医生应当能够给他们提供适当的意见。
　　
Although serum vitamin D level (25-hydroxyvitamin D) can be easily measured and is a widely available blood test, further studies are required to identify appropriate serum concentrations of vitamin D needed for optimal health.

尽管血清维生素D水平(25-羟基维生素D)是广为人知的血液测试，它可以轻易地被测量，但还需要更进一步的研究来确定对于理想健康来说血清中维生素D量多少才合适。
　　
The standard reference now recommended by the AAD to advise patients regarding their needed minimum intake levels is the National Academy of Sciences Institute of Medicine guidelines for vitamin D. Because of new developments regarding knowledge of the clinical benefit of vitamin D, current recommendations for adequate vitamin D intake levels established by the Institute of Medicine may be increased in the near future.

目前美国皮肤学会推荐给病人的这份指南特别建议病人注意他们所需要的最小摄入水平，这一标准来自美国美国国家科学院医学研究所。由于新技术的发展，随着对维生素D在临床上应用获益的了解，由医学研究院建立的目前这份指南中维生素D充足摄入水平在不久的将来有可能增加。
　　
The US Department of Agriculture Dietary Guidelines recommend that those at risk for vitamin D insufficiency receive supplementation with a total daily dose of 1000 IU vitamin D, according to the AAD statement.

参考美国皮肤病学会的说明，美国农业部的膳食指南推荐那些处于维生素D不足风险中的人每日采用总计1000IU剂量维生素D的营养补充剂。
　
The AAD recommends supplementation with 200 IU vitamin D from birth to age 50 years for those who are not at increased risk for vitamin D insufficiency. However, the American Academy of Pediatrics recommends supplementation with 400 IU vitamin D per day for children younger than 18 years of age, including infants.

美国皮肤科医学会建议50岁以下没有高维生素D摄入不足风险的人群每日使用200IU的维生素D。然而，美国儿科学会推荐18岁以下的儿童们每日补充400IU的维生素D，其中包括婴儿。

Because vitamin D can be toxic in high doses, the US Food and Nutrition Board has set an upper limit for safety for vitamin D intake of 2000 IU per day for individuals older than 12 months of age and 1000 IU per day for infants.

由于高剂量的维生素D有毒性，美国食品与营养协会已经设定了一个维生素D安全摄入高限，年龄超过12个月的个人每日2000IU，婴儿每日1000IU。

For vitamin D supplementation, vitamin D3 (cholecalciferol), which is the form of vitamin D naturally produced in the skin, is preferred to vitamin D2 (ergocalciferol).

对于维生素D补充剂，维生素D3(胆钙化醇)这种人体皮肤自然产生的形式优于维生素D2(麦角钙化醇)。

The updated AAD statement now emphasizes that there is no scientifically proven safe threshold for exposure to the sun or indoor tanning devices that optimizes vitamin D synthesis in the skin without increasing skin cancer risk. Laboratory research has shown that UV radiation from either the sun or tanning devices can cause oncogenic mutations in skin cells, and use of sunbeds has also been associated with increased risk for melanoma and squamous cell carcinoma. UV radiation exposure has also been linked to cataracts, premature aging, and immune suppression.

最新美国皮肤病协会的这份声明特别强调了一点，就是目前还没有确定通过日晒或是室内晒黑装置来在皮肤内自然合成维生素D而不增加皮肤癌患病风险的安全阈值。实验室的研究已经显示，无论是来自太阳还是室内晒黑装置的紫外线都能够造成皮肤细胞的突变，并且在晒日光浴也能够增加乳癌、黑色素瘤、鳞状细胞癌的患病几率。紫外线辐射还容易造成白内障、早衰以及免疫抑制。
　　
"It is well documented in the medical literature that unprotected exposure to UV radiation from natural sunlight or indoor tanning devices causes skin damage," Dr. Pariser said. "There is no current research available that provides a safe limit for sun exposure to maximize vitamin D production that does not put the individual's health at risk for developing skin cancer."

Pariser博士提到，在医学文献中已经有过明文规定，无保护性地暴露于自然光或室内晒黑装置的紫外线会造成皮肤的伤害。现在的研究无法做出伤害人体的实验，以至于无法得出究竟多少的晒日可以尽可能产生维生素D而不至于对健康产生患皮肤癌的风险。
　　
Low levels of vitamin D have been linked in numerous studies to greater risk for certain cancers and for some neurologic, autoimmune, and cardiovascular diseases, but clinical trials have not yet been performed to show a causal relationship of vitamin D to these diseases.

许多研究证实，维生素D摄入水平低下与某些癌症以及一些神经、自身免疫性、心血管系统疾病有关，但临床试验还没有证明维生素D与这些疾病之间的因果关系。
　　
"Contrary to some reported information about vitamin D and the prevention of certain cancers and diseases — other than for bone health — we simply need more clinical data to determine what role, if any, vitamin D plays in these conditions," Dr. Pariser said.

Pariser博士说：“与一些指出维生素D与预防某些癌症和疾病有关（而不仅是骨骼健康）的报道相反的是，我们仅仅是需要更多的临床资料来证明维生素D在这些条件下具有的作用。”
　　
The AAD still recommends avoiding use of tanning beds. The National Council on Skin Cancer Prevention recommends protection from UV exposure when outdoors by seeking the shade between 10 am and 4 pm whenever possible, generously applying sunscreen with a sun protection factor of at least 15, and wearing sun-protective clothing, including wide-brimmed hats, long sleeves, pants, and UV-protective sunglasses。

美国皮肤病学会仍然建议避免使用日光浴床。国民议会在皮肤癌预防方面推荐当上午10点与下午4点之间户外活动时，要想保护皮肤避免暴露在紫外线下就应当尽可能寻找荫凉，经常使用至少15个防晒系数的防晒霜并穿着防紫外线的服装，其中包括宽边帽、长长的袖子、裤子以及防紫外线的太阳镜。
　　
"For those who are concerned about vitamin D insufficiency, diet and vitamin D supplementation are the most appropriate methods to obtain adequate vitamin D — it is not appropriate to seek exposure to ultraviolet radiation," said National Council on Skin Cancer Prevention co-chair Henry Lim, MD, FAAD, chairman of dermatology at Henry Ford Hospital in Detroit, Michigan.

美国国民议会皮肤癌预防医学主席，底特律亨利福特医院皮肤学会长Henry Lim, MD, FAAD说：“对于那些关心维生素D缺乏的人来说，饮食以及维生素D补充剂是获取足量维生素D最恰当的方式，这比暴露在紫外线下要好得多。”

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