Thursday, July 29, 2010

碘盐争议中的几个基本概念与争论焦点

最近,关于食盐加碘的争议非常热烈。在争论中,许多比较专业的概念频频出现。不仅是普通公众,某些媒体和评论家对于它们的意义也不甚了了,使得许多议论是出于误解,甚至以讹传讹。这里先介绍几个基本概念,然后介绍碘盐争议的焦点。
碘摄入量与尿碘中间值
碘摄入量是指一个人平均每天吃进去的碘的总量。在饮用水和食物中,通常也会含有一些碘。不过,在多数地区,这部分碘的总量比较小,远远不能满足人体需求。所以,世界大多数地区,都是需要补碘的。只有在少数沿海地区,饮用水和农产品中可能含有的碘量比较高,如果食物中经常有海产品的话,碘量就更大。对于个人而言,这个量很难准确计算,往往是估计一个地区的平均值。
尿碘含量是科学研究中经常使用的参数,英文简称UI值。它是指尿液中的碘含量,通常以每升尿液中的微克数来表示。因为摄入人体内的碘会有90%以上最终会进入尿液,这个量也可以比较灵敏地衡量摄入的碘的总水平。理论上说,可以测量一个人的尿碘含量。不过,这个值受被测当天饮食情况的影响很大,个人某天的尿碘值也意义不大。通常,也是测量一个地区的尿碘总体水平。准确地测量一个地区的尿碘水平应该收集人群在24小时之内的所有尿液,不过这样操作起来实在比较困难。实际操作中,通常取一个地区的一部分有代表性的人群,收集某一时间内的尿液,检测各自尿碘含量,然后取这些值的中间值,作为这一地区的“尿碘中间值”。统计发现,只要样本量足够大,这样得到的尿碘中间值可以代表通过24小时内的尿液得到的尿碘值。尿碘含量也可以用来估算碘的摄入量。按照美国卫生部提供的公式,尿碘中间值100(微克每升)大致相当于每天摄入量为150微克。
每日推荐量与最大安全上限
许多媒体引用世界卫生组织(WHO)的推荐每日摄入量,说某个地区的碘摄入量超过了这个标准多少之类。这个“每日推荐量”是指满足绝大多数人一天需求的量,简称RDA,有时也用“充足摄入量”,简称AI。意思是,对于大多数人来说,低于这个值可能是摄入不足,达到这个值就足够了。
最大安全上限的简称是UL,意思是目前的科学数据认为是安全的最大值。只要不超过这个值,就可以认为是安全的。而超过了这个值也不见得一定有害,只是目前的科学数据对其安全性难以判定。
根据这两个量的定义,不难看出,只要一种成分的摄入量在RDA和UL之间,就是充足安全的。通常,许多营养成分的RDA和UL之间都有相当大大的缓冲空间,比如钙,美国成年人的RDA值是1000毫克,而UL则是2500毫克。
应该注意的是,RDA和UL值都是人为选定的。人们到底需要多少,能够忍受多少而没有副作用,无法确切知道。这些数字是不同国家的主管部门和国际组织根据公开发表的科学文献,按照各自对于“安全”以及“充足”的理解制定出来的。当有新的重要的研究结果发表,改变了人们对事物的看法,这些推荐值和安全值就有可能修改。
疾病风险
对于碘的问题,毫无争议的是碘摄入不足会导致碘缺乏病,英文简称IDD,症状主要有甲状腺肿大、流产、婴幼儿及青少年发育迟缓等。
而碘过量可能导致的疾病风险,目前的研究结果是在碘缺乏地区提高碘摄入量的一段时期内,可能导致甲状腺功能亢进和自身免疫性甲状腺炎的发生率升高。这种风险有多大呢?丹麦的一项研究结果是六年中总的甲状腺功能亢进发生率从千分之一左右上升到了千分之一点四左右。而中国医科大学进行的一项研究结果结果比这要严重。他们根据体内的某种激素水平的变化来判定甲状腺功能亢进——也就是说,并非真的出现症状,而是无症状的早期激素水平变化,碘摄入量不足的地区发生率是0.2%,过量和超量的地区分别是2.6%和2.9%。
对于缺碘地区因为提高了碘摄入量而增加的发生率,比较广为接受的看法是在若干年(可达1至10年)后会恢复原始状态。应该注意到,在中国医科大学的那项研究中,“疾病”的判断是基于激素水平的升高而不是真的出现症状,在足够长的时间之后激素水平是否会下降还不能做出判断;其次是发生率从0.2%增加到2.6%,也还是只有一小部分人。虽然说这样的一个增加足以引起人们的重视,但是跟许多人传说的“吃碘盐会导致大脖子病”完全不是一回事。
碘盐之争,焦点在哪里
这场碘盐之争,人们有没有“选择权”是没有意义的。有了“选择权”,人们依然需要可靠的科学基础才能正确选择,否则就只能被谣言所左右。从技术的角度说,这个争论的焦点在于:我们需要多少碘?食盐中的碘是否过多了?
我们需要多少碘的问题还好回答,科学界也基本上有了共识。按照2007年世卫组织、国际控制碘缺乏症理事会和联合国儿童基金会的联合报告,成人的推荐每日摄入量是150微克,怀孕和哺乳期的妇女是250微克,未成年人按年龄有所减少。美国的推荐数字与这个差不多。而最大安全上限则差别比较大。对于成人,美国的标准是1100微克,而欧盟则是600微克。世卫组织等机构的建议则是按照尿碘中间值做出的,100~200之间是充足,200~300是过量,300以上是超量。过量可能导致敏感人群出现甲状腺功能异常,而超量则是普通人群也可能增加风险。如果按照尿碘中间值和每日摄入量之间的关系,世卫组织和欧盟的安全标准要接近一些。
但是有一些实际数字又与此相当不符。比如日本居民的碘摄入量一般远远超过这些“安全标准”。在日本北部,居民日常大量食用海带之类的海产品,碘的摄入量高达50000~80000微克,是这些“安全标准”的百倍以上。而美国,在上个世纪七十年代,尿碘中间值是320左右,当时的碘缺乏病发生率是3%,而怀孕妇女的碘缺乏病发病率是1%。但是由于后来美国人的盐摄入量下降以及加工食品增多(加工食品少用碘盐),美国的尿碘中间值在上世纪九十年代到世纪末之间降到了200以下。按照世卫组织的标准,这个值很充足而且合理。但是美国这一时期普通人群的碘缺乏病发生率上升到了12%,而怀孕妇女中的发生率也上升到了7%。所以有美国学者提出,美国人群的碘摄入量处于不足和充足的边缘,应该把每日摄入量提高到300~400微克,以恢复上世纪七十年代的碘缺乏病低发生率。
中国的碘摄入量到底是什么水平呢?中国各地的差别比较大,在中国医科大学发表在《新英格兰医学杂志》上的那项著名研究里,所选择的三个县的尿碘中间值分别是84,243和651。
原文网址:http://songshuhui.net/archives/40629.html

How I Learned to Stop Worrying and Love Technology


by Ricardo Gutierrez

Every creative field, maybe even every field, has been shaken by technology in recent history. Technology can be cruel. With one hand it gives and with the other it takes. It doesn't do it because it hates you. It just really doesn't care about you. It doesn't even know you exist. You are Molly Ringwald in the first act of every '80s movie she was in and technology is the boy she's crushing on.

I know, I know, it hurts. Take it from me though, that huge wave of technological progress sweeping over [insert your career field here] doesn't have to mean the end. At least, not the end of your career. Your life will definitely change. Your field will too. If you want to survive, I'll help you. Four pronged approach:

First: Stop fighting it. You can't win that war. You can't even win the battle. You can't even send your dad back in time to kill the machine that is bent on killing the unborn you and taking your future job. Or something like that. You hear me movie studios? I'm glad the Old Grey Lady is starting to listen. I hope it's not too late for her. She's always been nice to me.

But seriously, the music industry was the first to get hit in the switch to digital, that I can think of. Everyone at the top resisted. They couldn't see their industry going away, not after windfalls a few years prior. Even the studios couldn't imagine that they wouldn't be needed as much, seeing as it took so much money to record an album. Technology changed that. For over 50 years technology had refined the process, made the music sound better, even more expensive to make. Then, with very little warning, technology changed it all so that the means of production became reachable to a larger percentage of the population. Add to that the huge shift in distribution channels from a tangible physical medium to the portable, invisible, digital realm. Companies thought they could fight the technology and that people would loyally side with them and their methods. That didn't work so well.


Which leads me to, Second: Stay small. Or as small as possible. I like to refer to big, huge companies as dinosaurs. Because they are so big they are targets. When a catastrophe happens they have nowhere to hide and slow to change. They are so top-loaded that their massive size is bad for survival. In order to hide from an incoming comet it takes too many people to make the decision along the way from the teeny brain to the huge feet. Too late, cloud of fire and dust.

If you stay only as large as you need to be, then switching at a moments notice doesn't take as much effort and it doesn't take tons people several years to decide to change. Technology is learning to sprint now and it just bought some brand new running shoes. You gotta be able to keep up and adapt.

And there is Third (which is closely related to the first): Use the technology to play to your strengths. If your arms are too short to box with God, then learn a new style that gives you the advantage. Get in close and scramble with him. Put him on the mat and get him to tap out. Don't try to go for a knock-out, your just going to embarrass yourself. 

Don't jump on every new technology trend and look like the person riding the bandwagon. Try everything out, behind closed doors, but only publicly commit to technology that emphasizes and compliments the things you already do well, while helping you stay in the race. Most people can smell fake moves a mile away. And if anyone asks you why you don't have some new hip and fancy service, find some polite way of telling them they don't know what the fuck they are talking about. Or maybe it's better just to let them know that you've tried it but it doesn't add anything to your brand or services.

Hollywood, let me pull you aside here to let you know something, you can't make every movie in 3D. I mean, you can, that's your choice, but people still just want a good movie.

I saw several recording studios try to offer every service that existed under the sun. They wanted to corner every market, which meant specialized machines for all those different tasks, more workers with special skills and increased overhead. Some of those markets had false-starts or barely exist anymore so that was a loss on investment of time and money. Have any of you purchased a DVD-A or SACD lately? Exactly. Some other markets still exist as a niche but now barely cover the cost of maintenance. Vinyl, I'm looking in your general direction. I love you but we both know it's true. But what these studios weren't doing is making themselves indispensable to the music community in the areas they excelled in.

Playing to your strengths means knowing exactly what those strengths are, which often means knowing what others weaknesses are (notice I didn't call them enemies, you never know when you have to combine your efforts so the both of you win. It's better not to demonize them). You really have to be on some Art of War type of shit. You have to see your path to victory and almost rig the game so you can't loose.

Technology has taken huge jumps forward in my field. A lot of people can do mastering work all within a computer, with plug-ins. I don't knock anyone for the way they do their thing, I just have my own way. I use computers to do some tasks, but the large majority of my work still happens in specialized gear that most people aren't going to have in their homes and small project studios. The way I use my tools influences the way I think about the material I'm working on. The tactile nature of knobs and switches changes my process and, I feel, the results. But when I need to use a plug-in for something, I'm not going to spit in it's face, I'll use it. I've crafted my "sound" around my process and people pay for that and for results. At the same time, I'd be an idiot to be a Luddite about plug-ins, plus a hypocrite since my whole career exists because of technology itself.

You do all of those things so that you get to Fourth: Stick around long enough and the work will be there. These industries aren't totally disappearing, though they may change so much that we barely recognize them. People will still be reading even if we don't print on paper anymore, people will still be watching programming of all types even if it isn't on the television. 

We have to stop thinking of the methods as static and see them as fluid. You have be Neo at the end of the first film. You have see the ones and zeros. You have to see the impermanence of all these edifices we created, but know that we can always create new ones. The old modes will still exist, some people will prefer paper books like some folks prefer music on vinyl, but most movement and commerce will not be happening there.

Same goes for movies, though that one is tricky because a lot of people go for the experience of the picture and sound in the theater. But at the same time, I know people who have built up amazing home theaters in their living rooms because, in the long run, it's cheaper than taking a family of four out to the movies all the time. And as time moves forward, the technology gets cheaper while movie ticket prices continue to go up. Who do you think will win that one?

A side-effect of all this is that you may be making less money than you're used to and you'll probably be working harder for it. This especially goes for freelancers, but it goes for companies as well. This may just be temporary, but who knows. It's hard, I know. I'm still struggling to stay alive, and I may fail someday, but I'm doing what I love to do and I would be miserable doing anything else.

I don't even think it's too late for record labels or recoding studios. I have hope. The market has just changed and they need to figure out how to adapt to it before the next comet strikes. People have been experiencing music since we hollowed out bones for flutes and first made drums from animal skins. It's an integral part of our humanity and people will be making music for a very long time to come. It's just that the way we experience it will continue to change, rapidly. Unfortunately, a lot of the music companies are still trying to plug round plastic pegs into what have become binary holes.

I realize I am oversimplifying matters a bit, in my own long-winded way, so that they work across several fields. Every field doesn't have the same specific worries and troubles. But that doesn't mean one field can't learn from the others example.

Sara's post yesterday, Pleading the Belly, sort of set me off in thinking about this all today. The idea of examining all the tumult of history and seeing that in the end "people go on living". I want us all to be good. I just think that we have to meditate on our particular fields in a way that's deeper than just "I need to be on the new shit". It's more like you have to create the "you" shit. The thing you do, in your way. It can be adapted to, and with, changing technologies, but even technology can't take it away.