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Your mother made you take them. Many doctors agree. Even the Flintstones seem to endorse them. But do you really need a multivitamin?
The answer is ... probably not, although much depends on your age, gender, diet and health. One thing is certain: A one-size-fits-all multivitamin can't precisely meet everyone's needs. People over 50 need extra vitamin B-12, but not as much iron as many multivitamins contain. Children who take adult multivitamins may be getting too much vitamin A. And many women need a separate supplement to get extra calcium, since it's too bulky to fit into a multivitamin.
No wonder the vitamin aisle is so confusing, as manufacturers tailor products for different population segments. One-A-Day brand alone offers 14 versions, from Men's 50+ Advantage to Vitacrave Gummies for kids.
Reading labels can lead to even more confusion. Recommended Dietary Allowances (RDA) for vitamins and minerals, which are set by the independent Institute of Medicine, differ by an individual's age and gender. But for convenience, the Food and Drug Administration requires dietary supplements to list a single Daily Value, usually the highest needed.
For some people, that's too high: The RDA for iron, for example, is 8 milligrams for men and postmenopausal women. But the Daily Value on supplement labels is 18 milligrams, the amount recommended for women of childbearing age. What's more, the Daily Values haven't been updated since 1968, even though the institute's recommendations for some vitamins and minerals have changed.
'In some cases, they are wildly off,' says Paul Coates, director of the National Institute of Health's Office of Dietary Supplements. An FDA spokeswoman said the agency is considering revisions.
There is no standard multivitamin formula. The term applies to any combination of vitamins and minerals in any strength, as long as they are listed on the label.
The label may not even exactly match what's in the bottle. ConsumerLab, a supplement-testing company, reported last week that 10 of 38 multivitamin brands tested contained either more or less of some ingredients than the label indicated.
And price was no predictor of quality. Some multivitamins selling for less than 10 cents a day performed better on the tests than those selling for 50 cents or more.
The Council for Responsible Nutrition, a trade group that represents most multivitamin and other supplement makers, says, 'It concerns us anytime ConsumerLab says we don't meet label claims,' says CRN's chief executive and president. Steven Mister. 'But there is nothing in the report that suggests that consumers are getting levels that will do them harm.'
Are multivitamins even necessary? The dietary supplement industry likens them to nutritional insurance—filling in gaps when people don't eat perfectly balanced meals.
That rationale has helped make multivitamins, introduced in the 1940s, the best-selling dietary supplement, with more than $4.8 billion in sales in 2008, according to Nutrition Business Journal. A third of American adults take them regularly. Use is particularly high among women, children, physicians, the elderly and people with high incomes, low body-mass indexes and healthy eating habits, according to government surveys.
Given those traits and demographics, people most likely to benefit from multivitamins—due to unhealthy habits—also are least likely to take them. Conversely, because people who take multivitamins tend to have other healthy habits, it's difficult to prove what effect multivitamins have, if any, in overall health.
Looking at randomized controlled trials, the gold standard for determining cause-and-effect, a NIH panel in 2007 concluded that 'the present evidence is insufficient to recommend either for or against the use of [multivitamins and minerals] by the American public to prevent chronic disease.' A 2003 U.S. Preventive Services Task Force report found insufficient evidence either for or against taking multivitamins to prevent cancer or cardiovascular disease.
The dietary-supplement trade group says observational studies have shown benefits, including a lower risk of cataracts and colon cancer, and fewer colds.
Such studies, though, can't determine cause and effect, only association. And several large observational trials have come to opposite conclusions.
A study in the American Journal of Epidemiology this year that followed 182,000 people in Hawaii and California for 11 years found no association between multivitamin use and deaths from cancer, cardiovascular disease or any cause.
Compared with over-the-counter and prescription drugs, dietary supplements are lightly regulated. Makers don't need to demonstrate that they are safe or effective. But there are limits to what they can claim. Ads that use terms such as 'support' breast health or mental alertness must note that such statements haven't been evaluated by the FDA and that the product isn't intended to diagnose, treat, cure or prevent any disease.
Still, a scientific consensus has emerged that some groups of people do require more of certain nutrients than they are likely to get from food. Women who might become pregnant should get an additional 400 micrograms a day of folic acid, to reduce the risk of serious neurological issues in a fetus that may occur even before a woman knows she is pregnant.
People over age 50 should get the recommended 2.4 micrograms of vitamin B-12 from supplements or fortified foods because they become less able to absorb it from food as they age. Vegetarians and vegans also need extra B-12.
Infants who are being breastfed should get 400 International Units (IUs) a day of supplement vitamin D until they are weaned. In fact, most Americans need 600 IUs per day, according to a 2010 report from the Institute of Medicine. People who get minimal sun exposure and don't consume much salmon or milk also should supplement their Vitamin D.
On the other hand, some people may get too much of certain nutrients, depending on their age and health, particularly if they use the current Daily Values listed on labels as a guide. For example, 100% of the current Daily Value for vitamin A is 5,000 IUs-which is over the Institute of Medicine's safe upper limit of 2,000 IUs for children and far beyond the RDA for children ages 1 through 3 of just 1,000 IUs. Excess vitamin A can cause headaches, hair loss, visual disturbances and a possibly increased risk of osteoporosis. And smokers should avoid taking extra beta carotene, which has been linked to increased risk of lung cancer.
The consumer-advocacy group Center for Science in the Public Interest has asked the FDA to require warning labels on multivitamins and other supplements for some of these conditions.
Officials at the dietary-supplement trade group say evidence of the need for such warnings is scant, and the upper limit for vitamins is still safe. 'That's not to say that if you cross that threshold, you will have a fatal condition,' says Duffy MacKay, a naturopathic doctor and CRN vice president.
Given all the complexities, it pays to discuss individual needs with a doctor, dietitian or other health professional. Some people may find the à la carte approach works best. Others may like the extra 'insurance' provided by a multivitamin targeted to their age and sex.
Dr. Coates, of the NIH, says based on the best evidence, 'If you are taking multivitamins, there is no reason to stop, and if you are not taking them, there is no reason to start. You are unlikely to harm yourself, whatever you're doing.'
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你妈妈非得让你吃这些东西。很多医生也赞同。就连动画节目《摩登原始人》(Flintstones)似乎也认可它们。但你真的需要服用复合维他命剂吗？
答案是……或许用不着，不过在很大程度上也要取决于你的年龄、性别、饮食和健康状况。有一件事是确定的：适合所有人的通用复合维他命剂肯定无法精确地满足每个人的需要。50岁以上的人需要额外补充维他命B-12，但不少的复合维他命剂中所含的铁元素对他们来说又过量了。儿童如果服用针对成人的复合维他命，就可能摄入过量维他命A。而很多女性需要单独补钙，因为钙的体积太大，无法合成到复合维他命剂当中。
怪不得林林总总的维他命产品让人如此困惑，因为生产厂商都会针对不同的人群定制产品。光是One-A-Day这个牌子就有14种不同的维他命产品，从50岁以上男性综合维他命(Men's 50+ Advantage)到针对儿童的复合维他命咀嚼软糖(Vitacrave Gummies)等等。
阅读产品上的标签可能让人更犯晕。维他命和矿物质的每日膳食推荐摄取量(Recommended Dietary Allowances)是由独立的美国医学研究院(Institute of Medicine)设定的，根据个人的年龄和性别而异。但为了方便起见，美国食品和药物管理局(Food and Drug Administration)要求膳食补充剂列出一个单一的每日摄入量，通常是所需的最高值。
对于一些人来说这个量就过头了：比如说男性和绝经后女性的铁元素每日推荐摄取量是8毫克。但补充剂标签上标明的每日摄入量为18毫克，这是针对育龄妇女的推荐摄入量。此外，每日摄入量自1968年以来就没有更新过，虽然美国医学研究院对于某些种类的维他命和矿物质的推荐摄入量已经有所改变。
美国国家卫生研究院(National Institutes of Health) 下属的膳食补充剂办公室(Office of Dietary Supplements)主任保罗?高特斯(Paul Coates)说，在有的情况下二者相差非常大。美国食品和药物管理局发言人说，该机构正在考虑修订事宜。
复合维他命剂的配方并没有通用标准。只要是含有多种维他命和矿物质，无论其含量多少，都可以叫这个名字，只要标签上列明所含成份即可。
标签上所列的甚至都未必与瓶子里的内容完全相符。对补充剂进行检测的公司消费者实验室(Consumer Lab)上周报告说，其检测的38个不同品牌的复合维他命剂当中，有10个品牌的产品所含成份的量高于或低于其标签标示的量。
还有，一分钱也未必就代表着一分货。在检测中，售价折合每日成本不到10美分的一些复合维他命剂的表现要好于每日成本在50美分甚至更高的产品。
代表大多数复合维他命剂和其他膳食补充剂生产商的行业组织诚信保健品协会(Council for Responsible Nutrition)说，消费者实验室每次一说我们的产品与标签所示不符，我们都会十分关注。但报告中并没有显示已经到了会有害于消费者的程度。
复合维他命剂是否确实必要？膳食补充剂行业将它们比作营养保险──当人们的一日三餐没有达到理想的均衡时，复合维他命剂就会填补其中的摄入不足的部分。
这种理论让上世纪40年代兴起的复合维他命剂成为最畅销的膳食补充剂。据《营养商业期刊》(Nutrition Business Journal)报导，2008年复合维他命剂的销售额超过48亿美元。三分之一的美国成年人经常服用复合维他命剂。政府调查显示，女性、儿童、医生、老年人服用的尤其多，此外还有收入高、体重系数低、注重健康饮食习惯的人群。
考虑到上述特色和人口统计资料，最有可能从复合维他命剂中受益的人群同时也是最不可能服用的，原因是他们不健康的习惯。相反，由于服用复合维他命剂的人往往在其他方面也保持着健康的习惯，因此很难证明复合维他命剂对于总体健康状况有何种作用、甚至到底有没有作用。
通过号称确定因果关系黄金标准的随机对照实验，美国国家卫生研究院的一个专家小组在2007年得出结论，认为当前的证据不足以推荐美国公众为预防慢性疾病而服用或不要服用复合维他命剂和矿物质。2003年美国联邦预防医学工作组(Preventive Services Task Force)的一份报告也发现，，对于预防癌症或心血管疾病，是服用还是不要服用复合维他命剂的问题，尚无足够的证据做出判断。
膳食补充剂行业组织宣称，观察性研究已经表明服用复合维他命剂对人体有益，包括降低白内障和结肠癌的风险，以及更少患上感冒。
不过这类研究无法证明其中的因果关系，只是表明二者相关联。而且有几项大规模的观察试验还得出了相反的结论。
《美国流行病学期刊》(American Journal of Epidemiology)今年刊登的一项研究在11年的时间里跟踪了夏威夷和加利福尼亚州的18.2万人，结果发现服用复合维他命剂与癌症、心血管疾病或任何原因引起的死亡之间都不存在相关关系。
相比非处方药和处方药，膳食补充剂没有受到太多监管。生产商并不需要证明它们安全或有效。但生产商宣称其产品能达到何种效果则受到限制。使用“有助于”乳腺健康或头脑清醒这类说法的广告必须注明，这些说法并未经食品和药物管理局评估，同时其产品也并非用于诊断、治疗、治愈或预防任何疾病。
不过，科学界已经有一致的意见，认为一些群体在能从食物中摄入的营养成份之外确实还需要补充特定的营养。可能怀孕的女性应当每日补充400微克的叶酸，以减少胎儿出现严重神经系统问题的风险，这种问题甚至有可能在女性知晓自己已经怀孕之前就会出现。
50岁以上的人应当从补充剂或强化食品中摄入每日推荐的2.4微克维他命B-12，因为随着身体老化，他们从食物中吸收这种成份的能力会减弱。素食主义者也需要额外补充B-12。
母乳喂养的婴幼儿在断奶之前应每日补充400国际单位的维他命D。事实上据美国医学研究院2010年的一份报告，大多数美国人每天都需要600国际单位的维他命D。平时很少晒太阳、也不怎么吃三文鱼或者喝牛奶的人也应当补充维他命D。
另一方面，根据人们的年龄和健康状况，一些人摄入的某些营养成份可能过量，尤其是如果他们以目前维他命产品标签上所列的每日摄入量作为依据的话。比如说，当前的维他命A每日摄入量全都写着5000国际单位，这就超过了美国医学研究院为儿童设定的2000国际单位的安全上限，更是远远高于食品和药物管理局针对1-3岁儿童设定的1000国际单位。过量摄入维他命A可能导致头痛、脱发、视力障碍，并可能加大骨质疏松症的风险。抽烟者应当避免摄入过量的β胡萝卜素，过量摄入已经被证实与肺癌风险升高有关。
消费者权益组织公众营养健康科学中心(Center for Science in the Public Interest)已经要求食品和药物管理局强制规定在复合维他命和其他补充剂产品上为上述一些情况设置警示标签。
膳食补充剂行业组织的官员说，能够证明有必要标示这种警告的证据不足，而且维他命摄入量的上限仍然是安全的。自然疗法医生、诚信保健品协会的副会长达菲?麦基(Duffy MacKay)说，这并不是说一旦你越过这个界限，就会出现致命的情况。
考虑到所有这些复杂情况，与医生、营养师或其他健康专业人士讨论一下个人需求还是有好处的。一些人或许会觉得缺哪样就补哪样的办法最有效。还有的人则可能喜欢针对其年龄和性别的复合维他命所提供的额外“保险”。
美国国家卫生研究院的高特斯说，照最佳证据来看，如果你正在服用复合维他命，没有理由停止服用，而如果你没有服用，也没有必要开始吃。不管怎样你都不太可能会伤到自己。
