<International Circulation>: I understand there have been some studies done where people were given vitamin D and showed no beneficial effect.

　　《国际循环》：据我所知已经有一些研究显示给患者使用维生素D并没有得到预期的临床获益。
　　Dr Michos: There are some studies looking at vitamin D and blood pressure and things like C-reactive protein and it did reduce some of these markers. The largest randomized clinical trial was the Women’s Health Initiative that had 36000 post-menopausal women. They were randomized to 400IU of vitamin D plus calcium versus placebo， and there was no difference in heart attacks or strokes. The problem was that they used a very low dose of vitamin D， only 400IU， which wouldn’t be expected to boost levels very much. Many of the women in the placebo arm got to take their own supplements， so there was not a lot of difference between the two groups. There is a clinical trial ongoing now called the VITAL Study which is going to randomize older men and women to 2000IU versus placebo. The problem with the current evidence is that most of these randomized trials were for osteoporosis， so they did not collect cardiovascular outcomes data， or they used low doses. The other big thing is， unlike a drug like a statin， you can get vitamin D if you go out in the sun or get vitamin D in your diet. So they might not be many differences between the two groups， the treated and the placebo， because you can get a lot of vitamin D outside of the trial. That may blunt any difference between the two arms. This does not mean vitamin is not important， it is just hard to study. I am also a big believer that there is no fixed dose， that everyone needs 1000IU or 2000IU. I think what matters biologically is having optimal blood levels in the 30-50mg/dl range such that if someone gets adequate sunlight exposure， they might not need to take any supplements. On the other hand， if you are deficient， you might need much higher doses like 50000IU/week to get up to the normal range. I think it is a problem that there is no one fixed dose for everyone because based on genetics and your BMI and how much sun you get， people need different amounts to get their levels within an adequate range. Those are the challenges with getting randomized clinical trial data to show cardiovascular benefit.

　　Dr Michos: 有一些小规模的临床试验观察了维生素D和血压以及如C反应蛋白之间的关系，并且这些研究的结果显示维生素D确实能降低这些标志物。最大的随机临床试验是WHI试验（Women’s Health Initiative），它入选了36000例绝经后女性，这些人被随机分配为接受400 IU维生素D加钙剂或安慰剂治疗，结果显示两组之间在心脏病和卒中方面并没有差异。这个研究的问题是他们使用的维生素D剂量非常低，只有400 IU，这个剂量预计不会使维生素D的水平有很大的提高。而试验安慰剂组中的女性会自行补充维生素，因此两组之间不会有太大的差异。现在有一个名为VITAL的临床试验正在进行，这个试验准备把老年男性和女性随机分配至2000 IU维生素D治疗组和安慰剂组，这个剂量要明显高于之前试验中所用到的剂量。目前我们所获得的证据的问题在于大多数研究维生素D的试验都是观察骨质疏松的随机试验，因此他们并没有搜集心血管疾病的相关资料，他们在试验中用的维生素D剂量很小，并且最大的问题是不像其他的药物比如他汀类药物，在他汀和安慰剂的对比中安慰剂组是不会获得他汀药物的，而在维生素D的试验中，安慰剂组的患者也能通过进行户外活动晒太阳或者从饮食中获取维生素D。因此在这样的情况下试验中治疗组和安慰剂组之间的差异可能就不会太大，因为被研究者能在试验之外获得充足的维生素D。这有可能使两组中的任何差异缩小，所以这样的结果并不代表维生素D没有重要的作用，其实只是非常难于进行试验。我同时还非常坚信维生素D的治疗没有固定的剂量，没人大概需要1000 IU或 2000 IU。我认为要想使维生素D起生物学作用最佳的血液浓度应该是30~50 mg/dl，因此如果一些人能获得足够的阳光照射，他们可能不需要服用任何补充剂。从另一方面来说，如果你缺乏维生素D，你就可能需要更高的剂量比如每周50000 IU来达到正常值水平。我认为问题是每个人所需的维生素D量并不是固定的，因为你的需要量取决于你的基因、BMI和你获得了多少阳光，人们要达到够的维生素D水平所需要的维生素D量是不同的。这些就是进行随机临床试验证明维生素D有益于心血管疾病所需要面临的巨大挑战。
 

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