[This excellent review does not inclued the latest knowledge that this vitamin (hormone) can prevent or treat Alzheimer's dementia: http://tw.myblog.yahoo.com/jw!GAJfq5CREwTFZ1gGiWhZt.zp/article?mid=9260 ]
Vitamin D
Since 2008, the author has been invited in succession to deliver speeches on many occasions in the year end, such as for the Philadelphia Taiwanese Medical Association, Philadelphia Chinese Cultural Center/ Ming Tak Chinese School, Delaware State Chinese Activity Center, and TIMA in New York, to discuss sunshine vitamin and holistic health. Now, the speech content is summarized as follows, provided as a reference for everyone.
Vitamin D is a kind of fat-soluble vitamin. Its discovery is derived mainly from rickets in the 18th Century. At that time, the Industrial Revolution took off, and people in Europe and America all migrated, in great numbers, to industrial cities. In English cities, such as Glasgow, there were many crowded buildings, as well as houses beside dark and dim alleys, and hazy weather. Consequently, many children living there locally suffered from rickets. Other European industrial countries also had the same problem. Approximately 100~200 years later, through explorations were successively undertaken jointly by many doctors and scientists, people came to realize that rickets results from a lack of sunshine; also, sunshine is a requirement for facilitating the formation of Vitamin D in human bodies. Vitamin D can help in the absorption and metabolism of calcium and phosphorous in the small intestines, to maintain bone health. Cod Liver Oil contains Vitamin D, and prevented and cured rickets effectively at that time. Adolf Windaus, a German who had confirmed the structure of Vitamin D, won the Nobel Prize in Chemistry in 1928.
Due to such a historical cause, it was generally believed that Vitamin D was related only with bone health, or that there was no need to worry about Vitamin D ingestion as long as one had a balanced diet. However, many surveys have indicated that modern people lack Vitamin D seriously and generally. Inadequate in vivo Vitamin D has a close connection with serious health problems, such as Osteoporosis, many cancers (Colon Cancer, Breast Cancer, Prostate Cancer, Pancreatic Cancer, etc.), hypertension, heart diseases, Type I Diabetes, Rheumatoid Arthritis (RA), Multiple Sclerosis (MS), etc.
First of all, we should know: In the process of human evolution, it was designed that Vitamin D should be produced within the human body. Through the radiation of UVB (wavelength=290-320 nm) in UV ray, its precursor “7-dehydro－cholesterol” under our very thin epidermis can be converted into Vitamin D. Therefore, Vitamin D is also called the “Sunshine Vitamin”. In ancient times, Anthropoids, the faraway ancestors of human beings, exposed their entire bodies to the sun. In the agriculture age, owing to the lifestyle of “Going out to work in the sunrise and going back home at sunset”, people could obtain long-term sunshine nourishment naturally and hence produce adequate Vitamin D by themselves. However, as civilization makes progress, general clothing has begun to cover almost 95% of the skin. In modern life, people spend most of day time working indoors, living under electric lights all day long. When winter comes, people tend to come into contact with no sunshine for a long time. Even though people get the chance to be exposed to the sun, they always instantly apply layers of sun block, use parasols, and wear hats. Everyone believes that sun exposure will result in skin cancer or a suntan, which will speed up wrinkles and black spots— the great enemy of whitening.
However, are UV rays, especially UVB, really bad? Of course, too much exposure to the sun will do harm to the skin and increase the risk of skin caner. Nevertheless, sun exposure is the main source of Vitamin D in a human body. An appropriate degree of sunshine is necessary for human health.
The Vitamin D produced in the skin is Vitamin D3. Then, it undergoes hydroxylation twice through liver and kidneys, to form 25（OH）D3（calcidiol）first and then be converted into active Vitamin D －－1, 25（OH）2 D3（calcitriol）. In the status of activation, Vitamin D can be viewed as a hormone. In addition to bones and muscles, its receptors exist widely in the cell nucleuses in the cells of other organs, such as the brain, heart, breast, and prostate, as well as white blood cells, so as to control gene expression, which is a kind of hormone function. Therefore, in addition to affecting bone mass, a lack of Vitamin D may affect the immune system, cell maintenance, pathological cancer changes, and more.
During recent years, the research reports on Vitamin D and diseases have become a very popular issue. Through many kinds of paths, Vitamin D may protect the heart, e.g. reducing blood pressure, or inhibiting inflammation and reducing coronary artery calcification. It may also have an influence on cardiac muscles, by being able to reduce heart failure, respiratory tract infection, etc. Vitamin D has diversified mechanisms in cancer control. Researches have indicated that it serves the function of resisting tumor cell growth and inhibiting Angiogenesis, so as to inhibit tumor metastasis and further invasion. In the last step of Vitamin D activation, when it becomes active VitaminＤ－1,25（OH）2D3（calcitriol）, it not only produces 1-hydroxylase in kidneys, a fact we have known previously, but also in the cells of many organs. It can form active Vitamin D locally, which is directly embedded in the Vitamin D receptors in cell nucleus to control the cell cycle, specialization and apoptosis. It can also regulate gene expression of growth factors, and enable the immune system to work normally.
Many more reports have indicated that adequate in vivo Vitamin D content has a close connection with human health, while the UVB in UV rays is the source necessary for Vitamin D production in the human body. Compared with people in the south, being exposed to the sun much more, people in Northeast America and Nordic region, in which the latitude is higher, have a greater chance to suffer from cancers such as colorectal cancer, breast cancer, and prostate cancer, as well as heart disease. Heart disease occurs in winter mostly, when sunshine is scarcer. Skin melanin reduces the absorption of UV rays, because darker skin absorbs less sunshine. Therefore, African North-Americans generally lack Vitamin D, and are highly susceptible to diseases such as hypertension, etc. Also, the Vitamin D in a fat person will be compressed by his/her excessive fat, and is unable to be easily utilized. Thus, a fat person usually has a lower serum concentration of Vitamin D. Additionally, what deserves our attention is that many young mothers choose to breastfeed their babies at present. Of course, breast milk is the most perfect food for babies. However, a lack of Vitamin D often occurs. Therefore, a baby who is completely breastfed should be supplemented with Vitamin D, while a breastfeeding mother usually needs to supplement herself with Vitamin D.
Vitamin D can help in the absorption and metabolism of calcium and phosphorous in the small intestines. The public usually considers bone protection to be achieved merely through calcium ingestion. However, if Vitamin D is insufficient, calcium absorption is poor, and people may still suffer from osteoporosis. In addition, Vitamin D can maintain the coordination between nerves and muscles for muscles to have much more strength, and thus preventing falling-down and fracturing a bone. Thus, calcium and Vitamin D should work together, so as to effectively “protect bone density and prevent falling-down”.For elderly people, the function of producing Vitamin D in their bodies is far poorer than that in their youth. If they are exposed to the sun less, they tend to lack Vitamin D even more. Consequently, in addition to suffering from osteoporosis more easily, they may have a greater chance to suffer from cancers or other immunity disorder diseases
Approximately 90% of the Vitamin D in a human body comes from unscheduled sun exposure. When exposed to UVB radiation, the skin is able to produce tremendous amounts of Vitamin D very quickly. Sun exposure will not result in too much Vitamin D, because a human body has a regulating mechanism— it can increase melanin to absorb and block sunshine, making a person’s skin “become darker”;on the other hand, it will automatically dissolve excessive Vitamin D and the precursor. If a person with lighter skin (ex. white man) has his/her whole body exposed to the sun at noon in the summer for 10~20 minutes, about 10,000-20,000IU (international units) of Vitamin D can be produced in his/her body before his/her skin begins to become red but not suntanned yet— such a quantity is equal to drinking 200 cups of milk（100IU/8oz）supplemented with Vitamin D or taking 50 capsules of multi-vitamins（400IU/per capsule）. Experts recommend people to have moderate sensible sun exposure：First, from 10:00a.m to 3:00p.m., do not apply sun block on the skin, to let your skin (except facial skin) such as your back, both arms and legs be exposed to the sun for 10~20 minutes; then, apply sun block on your skin or put on a hat or clothes. Thus, by exposing 1/3~1/4 of all of your skin to the sun 2~3 times every week, you can have adequate Vitamin D ingestion. Non-white persons or people with darker skin should be exposed to the sun even longer. Thicker clouds, air pollution, the glass of windows in houses or cars, as well as clothes, will also block most UVB radiation, and further affect Vitamin D synthesis. In regions whose latitude is above 30°, such as those in the north of the line drawn from Los Angeles, California to Charlottesville, the UVB radiation there is inadequate in autumn and winter. In these places, people are unable to produce Vitamin D in their bodies in winter, no matter how hard they’ve tried to expose themselves to the sun.
Another point we should know is: Natural food contains little Vitamin D. As for plants, mushrooms, after being exposed to the sun, will contain Vitamin D2, which is similar to Vitamin D3 in human bodies but not exactly the same. Fatty fish, such as salmon and tuna, contain higher quantities of Vitamin D3. However, it has to be obtained through the food chain. If these fish are farm-raised, the Vitamin D in them will be reduced substantially. The Vitamin D added in milk is stipulated to be 100IU/per serving.
Therefore, moderate sensible sun exposure is the most economic and safest way to obtain adequate Vitamin D. If a person is unwilling or unable to be exposed to the sun, he/she should take a Vitamin D supplement. Nowadays, the Daily Recommended Allowance (RDA) of Vitamin D suggested in the USA is 200IU~600 IU. However, such allowances were enacted many years ago, aiming to prevent children from getting rickets. Recent scientific findings have indicated that such recommended allowances are too low to stay holistically healthy. However, how much Vitamin D is moderate? Dr. Reinhold Vieth in Canada has undertaken detailed analyses aimed at this. First, he asked: In ancient times, our ancestors exposed their almost-naked bodies to the sun; in such a circumstance, how much Vitamin D is a human being able to produce? He found out: Some African aborigines, South American farmers or beach lifeguards often contain 50-100 ng/ml of vitamin D serum (25(OH)D), or even higher. Therefore, such concentration levels should be the safest range that a human body can endure. The Vitamin D Council in the non-governmental circles in the USA suggests that a general person should try to keep a serum concentration of 40-70 ng/ml all year round.
At present, the daily limit of Vitamin D ingestion stipulated by the US Health Research Center is 50μg (2,000 IU). The public has a deeply-rooted concept that too much ingestion will cause intoxication. However, actual cases of intoxication caused by Vitamin D are rare. Nevertheless, it is necessary for people to regularly track their blood serum concentration of 25(OH) D. When undergoing a health checkup, a person should ask to receive such an examination (you can have the examination of 25(OH)D subsidized via general insurance now). First, you can check whether you lack Vitamin D. Then, check and see how much the concentration has increased, after you begin to take Vitamin D. Also, be careful that the vitamin D serum (25(OH) D) level should be within a safe range. Additionally, when taking a Vitamin D supplement, you should take cholecalciferol（D3）similar to the one produced within your body, and you’d be better off not taking ergocalciferol（D2）, which is derived from yeast and phytosterol.
In June 2007, the Canadian Cancer Society recommended that an adult should ingest 1,000IU of Vitamin D daily, which is even indispensable for people with darker skin or in the winter. Pregnant or breast-feeding women should ingest 2,000IU daily. In October 2008, the American Academy of Pediatrics also enhanced the daily RDA for babies and adolescents to be 400IU daily, from the original 200 IU. In November 2008, 18 professors in the University of California signed their names together, appealing to the government’s health institution to enhance the daily RDA of Vitamin D to be 2,000 IU. According to the results of epidemiology, Edward Giovannucci, a MD and ScD in Harvard University, estimated that the mortality of the aforementioned fatal cancers can be reduced by 29% if an American can ingest 1,500IU of Vitamin D every day.
The lack of Vitamin D has become a problem worldwide. In the USA, Europe and other places, more than 50% of children and adults are exposed to such a risk. The lack of Vitamin D has also become an often neglected medical problem. Doctors seldom perform checks on Vitamin D to see whether patients lack Vitamin D. Some patients have pain all over their body, and they were once diagnosed with fibromyalgia or they just keep on taking pain-killers. In fact, what they suffer from is osteomalacia, caused by a lack of Vitamin D. Other chronic illness, such as migraines, winter depression, poor gastrointestinal function, sense of fatigue, etc. are also connected with a lack of Vitamin D. Before 1930, there were no antibiotics at all; sun bathing and UV ray bathing were generally acknowledged to be the good ways to cure germs and viruses, e.g. pulmonary tuberculosis, pneumonia. During recent years, research findings have indicated that Vitamin D is indeed able to prompt in vivo white blood cells to generate cathelicidin, a kind of natural and widely-efficacious antibiotic, in human bodies, able to kill many kinds of germs and enhance a person’s resistance to TB and influenza.
Please do not forget: sunshine, air and water are indispensable for life survival. We can even say that sunshine enables our bodies to produce the Vitamin D that forms the “photosynthesis” in our bodies.
Everyone should be aware of his/her Vitamin D ingestion, and please have moderate sensible sun exposure or take Vitamin D.
Finally, I wish everyone stay healthy mentally and physically, and to lead a safe and joyful life!
撰稿者：林少光Sally Lee
海外談維他命D
筆者2008起曾先後應邀於年底在大費城臺灣人醫師學會，大費城華人文教中心/明德中文學校,德拉瓦州華人活動中心及紐約慈濟會等處演講，討論陽光維他命與整體健康。今將演講內容摘要如下，以供鄉親參考。
維他命D是一種脂溶性維他命，它的發現主要是由於十八世紀時的佝僂症(rickets)。 當時工業革命起飛，歐美人口紛紛遷移至工業大城。在英國城市如Glasgow多的是擁擠樓房、巷道幽暗的住屋，再加上陰霾的氣候，許多在當地居住的兒童都患佝僂病，其他歐洲工業國也突顯出同樣的問題。其後一兩百年經許多醫師和科學家前後共同的探討，才知道佝僂病是因為缺乏日照引起，而陽光又是促成人體生成維他命D的必要條件。維他命D能幫助小腸中鈣與磷的吸收代謝，維持骨骼健康。鱈魚魚肝油（cod liver oil）含有維他命D，在當時也有效的防治了兒童佝僂症。確定一維他命D結構的德籍Adolf Windaus在1928年獲諾貝爾獎化學獎。
因此歷史因緣，一般人認為維他命D只與骨骼健康有關，或者認為只要有均衡飲食就不必擔心維他命D攝取了。但許多調查指出現代的文明人普遍嚴重缺乏維他命D。體內維他命D不足與嚴重的健康問題如骨鬆症、諸多癌症（大腸癌、乳癌、攝護腺癌、胰臟癌等）、高血壓、心臟疾病、第一型糖尿病、風濕性關節炎、多發性硬化症等都有密切關聯。
我們首先要知道：人類在進化過程中，維他命D是被其設計為應在自己人體內製造的。它的先驅體7-dehydro－cholesterol在我們薄如細紗的表皮下，經紫外線陽光UVB（波長290-320 nm）的照射，便可轉成維生素D。因之維生素D也被稱為“陽光維他命”（Sunshine Vitamin）。想當年我們老祖先類人猿的全身都暴露在太陽下，而耕農時代的「日出而作，日落而息」的生活方式，人們很自然的長期受到陽光的滋養，自身製造足夠的維他命D。但隨著文明的進步，一般的衣著掩蓋了己幾乎95%的皮膚，現代的生活，人們白天大部份的時間都在室內工作，成天在電燈下生活。冬天一到，更是長時間不見陽光。即使有機會露身太陽下，也會慌忙不迭的塗上一層層的防曬劑、打陽傘、戴帽子，大家都相信曬太陽會得皮膚癌，會曬傷皮膚，加速皺紋與黑斑，更是美白的大敵。
然而，紫外線陽光，尤其是UVB真的是個大壞蛋嗎？當然過度曬太陽會傷皮膚與增加患皮膚癌的可能性，但曬陽光是人體維他命D的主要來源。適度的日照陽光是人體健康所需的。
在皮膚製造的維他命Ｄ為維他命Ｄ３，它再通過肝臟與腎臟的兩次之羥化，先成25（OH）D3（calcidiol），再變為活性維他命Ｄ－－1,25（OH）2 D3（calcitriol）。維生素 D於活化狀態時，可以被視為荷爾蒙。它的受體除了在骨骼與肌肉外，更廣泛存在其他器官中 如腦、心臟、乳房、攝護腺、白血球等細胞的細胞核中，管控基因的表達，是屬於荷爾蒙的作用。因此缺乏維他命D除會影響骨質外，還可能影響到免疫系統，細胞維修，癌症病變等。
近幾年，維他命D與疾病的研究報導是非常熱門的項目。維他命D可能透過多種途徑保護心臟-如降低血壓，或有抑制發炎，減少冠狀動脈鈣化，也可能影響心肌，可以減少心臟衰竭及呼吸道感染等。維他命Ｄ抑癌有多方面的機制。研究顯示它具有抗腫瘤細胞生長及抑制血管增生的作用，從而抑制腫瘤轉移侵襲。維他命D最後一步活化的步驟，成為活性維他命Ｄ－1,25（OH）2D3（calcitriol）時，不僅只在以前所知的腎臟，許多器官的細胞中都有1-hydroxylase羥化脢，能就地生成活性的維他命Ｄ，它直接與細胞核中的維他命D感受體嵌合，控制細胞周期、分化與凋亡。它也能調節生長因子的基因表達，並使免疫系統正常運作。
這些越來越多的報告指出，體內充足的維他命D含量與人體的健康息息相關，而陽光紫外線的UVB是人體產生維生素D的必須來源。在緯度偏高的美國東北區和北歐地區比起陽光更多的南方，人們得直腸癌、乳癌、攝護腺癌等癌症和心臟病都較高。而心臟病最常發生於陽光稀少的冬季。皮膚的黑色素降低紫外線的吸收，暗色皮膚吸收比較少的陽光，因此北美非裔族普遍缺乏維他命D，得高血壓等病之病率也高。又肥胖者之維他命D被身體多的油脂積壓，不容易利用，肥胖者的維他命D血液濃度低。另值得注意的是目前許多年輕的母親都選擇以母乳餵小寶寶。當然母乳是嬰幼兒最完美的食物，但經常維他命D不足。因此，完全食母乳的嬰兒應該另外補充維他命D，餵母乳母親通常也需要補充維他命D。
維他命D能幫助小腸中鈣與磷的吸收代謝。大眾或以為只要攝取鈣質就能保骨，但若維他命D不足，鈣質吸收差，照樣可能骨鬆。此外，維他命D可維持神經與肌肉的協調，使肌肉較有力量，可較少跌倒骨折，因此鈣與維他命D必須一起作用，才能對骨骼有效的「保密防跌」。年長者身體製造維他命D的功能遠遜於年輕時，如果再加上少見陽光，會更缺乏維他命D，因此除較易骨折骨鬆外，也可能增加得癌症與其他免疫力失調的疾病。
人體90%的維他命D來自於不經意的日照。皮膚受UVB的照射便能非常快速的製造大量的維他命D，日曬陽光不會造成過多的維他命D，因身體有調節的機制，一方面增加黑色素吸擋日光，也就是“曬黑了”；另方面會自動銷解過多的維他命D與其前驅物。膚色淡的人（如白人）夏天中午全身日照曬一二十分鐘，皮膚剛剛泛紅而未曬傷之前，體內可產生10,000-20,000IU (國際單位)之維他命D（相當於喝兩百杯添加維他命D的牛奶（100IU/8oz），或吃上50顆綜合維他命丸（400IU/顆））。專案建議採用”適度日曬”(moderate sensible sun exposure)：在早上十點與下午三點之間，先不要擦防曬劑，讓身體除臉部以外的皮膚如背部、雙手臂、腿部等先曬太陽約十至二十分鐘的時間，然後再擦上防曬劑或加衣帽等。這樣全身三分之一到四分之一的皮膚每週日曬兩三次，就可攝取足夠的維他命D。非白人、膚色較黑者須要曬更久些。雲層厚，空氣污染，房子、車子窗戶的玻璃，衣服也會擋住大部份UVB照射，進而影響到維他命D的合成。緯度高於三十度如加州Los Angeles與北卡州Charlottesville畫一條線以北的地區，其秋冬季節的UVB照射不足，在這些地方冬天再怎麼曬太陽，身體也無法製造維他命D。
另一點要知道的是：天然食物中極少含有維他命D．植物如日曬香菇有維他命D２，與人體內維他命D３類似但不相同．肥魚如salmon, tuna 等魚含有較高量之維他命D3，但這些必須經食物鏈得來．如果魚是farm-raised，則其維他命D大減．牛奶中添加的規定為100IU/serving．
所以通過自己適度的日曬，是得到充足維他命D之最經濟而安全的方法．如果不願意，或無法曬到太陽，就要考慮服用維他命D補充品。現今美國維他命D的建議用量（RDA）是每天攝取200 IU至 600 IU。但是這些用量是多年前基於預防兒童得佝僂症而制定的。近來的科學證據顯示，為保持整體健康，這些建議攝取量太低。但要多少的維他命D才算是適度呢？加拿大的Dr. Reinhold Vieth就此做仔細的分析。他首先問，在遠古時我們的祖先幾乎全身光在太陽下，在類似情況下人類能製造出多少維他命D？他發現在有些非洲土著民，南美農民或海灘救生員體內血液維他D－25(OH)D－含量經常維持在這50-100 ng/ml或甚至高些。所以這濃度應該是人體能耐受的安全度。美國民間的The Vitamin D Council建議一般人終年應設法維持40-70 ng/ml的血液濃度。
目前美國健康研究中心定日服維他命D上限是是50μg (2,000 IU)。大眾深植的觀念中認為攝取過多會中毒，其實發現真正維他命D中毒的案例極少。但定期追蹤血液25(OH)D的血液濃度是有必要的，做體檢時應要求作這一項檢查（現在一般保險可付，要求做25(OH)D)。首先可瞭解自己是否缺乏維他命D，然後看服用後增高多少，並注意25(OH)D的血液濃度在安全範圍內。又使用維他命D補充品，應採用與體內製造相同的cholecalciferol（D3），不宜用酵母及植物固醇來源的ergocalciferol（D2）。
加拿大癌症學會已於2007年6月建議成人每日服用維他命 D量應為1,000 IU，冬季時或黑膚者更每日不可或缺。懷孕或哺乳婦女每天用2,000
IU。美國小兒科醫師學會也在2008年10月把嬰兒至青少年建議服用量由每日200 IU提高至 400 IU。2008年11月加州大學有十八位教授連署呼籲政府衛生機構將維他命D
每日攝取建議量提高至2,000
IU 。哈佛大學的Edward
Giovannucci, MD, ScD以epidemiology 之結果估計，如果美國人能每天攝取維他命1,500 IU的維他命D，上述致命癌症的死亡率可以減少29%。
缺乏維他命D已是世界性問題，在美國、歐洲和其他各地有超過50%的孩童與成人暴露在這個風險中。維他命D不足也的是常受忽略的醫療問題。醫師很少檢查維他命D，查病人是否缺維他命D。有些病人全身疼痛，曾被診斷為纖維性肌炎（fibromyalgia），或只一直吃止痛藥。事實上病人是因為維他命D不足而起的軟骨病（osteomalacia）。其他慢性病如偏頭痛，冬日憂鬱症，胃腸不好、疲倦等也與維他命D不足有關。在1930年之前沒有抗生素，日光浴和紫外線浴是公認對治病菌病毒的好方法，如肺癆病和肺炎等。近年來的研究發現維他命D確能促使人體白血球生成人體自然廣效抗生素cathelicidin，能殺傷多種病菌並增強對TB及感冒菌等的抵抗力。
請大家不要忘了，陽光、空氣和水是生命生存所須。我們甚至可以說陽光使身體製造維他命D，是我們人體的「光合作用」。 請鄉親們一定要注意自己維他命D的攝取—以適度日曬或服用維他命D！
最後祝大家身心健康，生活安樂！
沒有留言:
張貼留言