回想一下你曾经历过或正在经历的中学时代，你和身边的同学们是不是总觉得自己睡不够？当你打着哈欠谈起自己的疲惫，老师和家长们可能会将其归因于熬夜刷手机和繁重的学业负担。《美国医学会杂志》（JAMA）上的一项调查显示，对于很大一部分儿童和年轻人，体内缺铁可能才是引发疲劳的“罪魁祸首”。月经会使人体流失大量的铁，是育龄期女性出现铁减少（iron deficiency）的最常见原因和重大风险因素，而这一问题的严重性远超许多医生的认知。
在了解缺铁对人体的影响之前，我们首先需要知道贫血是什么、正确诊断缺铁性贫血（iron deficiency anemia）的重要性，以及缺铁和贫血的关系。美国密歇根大学安娜堡分校医学院（University of Michigan Medical School in Ann Arbor）的儿科血液学专家、临床副教授安吉拉·韦安德（Angela Weyand）是这项研究的领导者。
贫血是指人体内的红细胞数量减少，血红蛋白水平偏低，缺铁性贫血是最常见的贫血类型，由铁缺乏引起，没有足量的铁，身体就无法在红细胞内产生足量的血红蛋白，从而无法运送氧气。一旦出现贫血，血液输送氧气的能力减弱，就可能引发多种问题，比如，疲劳。
很多人将缺铁与贫血混为一谈，但它们是两个不同的概念。缺铁是一个渐进的过程，人体会在相当长的一段时间内仅表现为轻度缺铁（铁缺乏症），但如果不重视这一问题并及时补铁的话，就会发展到严重阶段，患上缺铁性贫血。即使没有被确诊为缺铁性贫血，程度相对较轻的铁减少和铁缺乏症也会对人体产生多方面的影响，其中既包括身体能量水平的下滑，还会损害心理健康。
为了更精确地调查美国12~21岁女性的铁缺乏症患病率，韦安德团队研究了美国健康和营养检查调查（NHANES）的数据。这项美国疾病控制与预防中心（CDC）开展的全国性调查收集了一般人群的健康数据，包括人口统计数据、身体指标检测数据和病史数据等。
在排除患有其他疾病或存在其他共病情况的患者，以减少疾病对铁缺乏的影响后，研究人员从数据库筛选出近3500名12~21岁的未怀孕青少年女性，因为月经是导致铁缺乏和贫血的一大风险因素，这一过程会导致人体铁元素流失。研究人员以铁蛋白水平低于25μg/L作为患有铁缺乏症的指标，以世界卫生组织定义的血红蛋白在12.5~13mg/dL之间、同时铁蛋白水平低于25μg/L作为患有缺铁性贫血的指标，对她们的铁缺乏情况进行了分析。结果显示，38.6%的青少年女性存在缺铁问题，6%已经发展为缺铁性贫血。
早在2004年进行的一项中国孕妇、育龄妇女铁缺乏症患病率调查同样显示，全国20-29岁的育龄妇女铁减少、缺铁性贫血和铁缺乏症（铁减少+缺铁性贫血）患病率分别为34.4%、15.1%、49.5%，即近半数的中国青年女性存在缺铁问题。
更值得担忧的是，由于这些研究主要关注的都是年轻群体，如果她们尚未接受准确诊断，缺铁问题并不会自行好转。随着年龄增长，这一比例可能还会更高。谈到开展这项研究的初衷，韦安德表示，作为一名儿科血液病专家，她在临床工作中经常会接触到同时患有严重月经过多症（HMB）和重度缺铁性贫血的女孩，这是导致女性严重贫血的重要因素之一，但往往得不到应有的重视和正确的诊断。她由此开始怀疑，是否还有许多症状相对较轻的铁缺乏症和缺铁性贫血病例没有得到识别和确诊。
根据WHO标准，在全球范围内，缺铁性贫血的主要患病群体包括5岁以下儿童，特别是婴儿和2岁以下儿童、经期少女、育龄期女性及孕产妇。据估计，全世界约有5亿15~49岁育龄期女性和2.69亿6~59月龄儿童患有贫血。
既然缺铁问题如此普遍，医生们为何会经常忽视患者身上的缺铁和贫血迹象呢？韦安德认为，这一方面出于铁缺乏症引发的症状特异性不足，确实难以诊断。俗话说，“头痛医头，脚痛医脚”，症状往往与病灶密切相关，但缺铁和贫血的许多症状并不直接指向这一病因，甚至更像某种“现代病”：睡眠困难、易疲劳、抑郁、焦虑、脱发……
在当今这个时代，忙碌是人们的常态，这些症状普遍在许多人中广泛存在，既可能与缺铁相关，也可能确实是由其他因素引起的。比如睡眠困难和疲劳，很多人会将其归因于生活习惯问题。有些感到疲劳的人可能真的是因为睡不够、抽不出时间锻炼，或来不及为自己准备健康的饮食，即使是来找韦安德看诊的青少年群体，他们感受到的疲倦也可能会被归结为没有好好睡觉或学习压力过大。
还有一个原因是，这些症状都属于主观感受，因此会让人们轻视问题的严重性。比如脱发与缺铁相关，但人们往往对正常的脱发量缺乏清晰的认识。疲劳也是如此，每个人对疲劳的感知都不太一样，我们难以客观地评估疲劳程度。很多人会抱怨自己好累，但不知道累到什么程度才是值得被重视的？我们可能须要尝试将其视为一种疾病的症状，而不是简单地认为这只是一个在周末好好多睡一会就能解决的小问题。
Could Menstruation Be Causing Low Iron Levels?
Rachel Feltman: Picture the teens in your life. Are they getting enough sleep? If not, you might assume they’re just falling prey to late nights on social media and school-related stress. But research suggests that for a huge percentage of kids and young adults, low iron levels may be to blame for their fatigue. It turns out that menstruation poses a bigger risk to iron levels than many doctors realize.
For Scientific American’s Science Quickly, I’m Rachel Feltman. My guest today is Angela Weyand, a pediatric hematologist and clinical associate professor at the University of Michigan Medical School in Ann Arbor. She’s here to explain how iron deficiency can affect everything from energy levels to mental health—regardless of whether it leads to full-blown anemia—and why doctors so often miss it, especially in adolescents.
Thanks so much for coming on to chat today.
Angela Weyand: Thanks for having me.
Feltman: So let’s start with a pretty basic question: What is anemia, and why is it important that it’s properly diagnosed?
Weyand: Sure, so anemia is when your hemoglobin is low or kind of—we think about that as, like, the number of red blood cells, which are important cells that carry oxygen to all of your tissues. It’s incredibly prevalent and can cause a lot of problems; as you can imagine, it’s important that we get adequate oxygen to all of our tissues, and so when we’re anemic and it impairs our ability to do that, we can have a lot of different symptoms. Probably the most common that people think of is fatigue.
Feltman: So, when did you start to suspect that some cases of anemia were flying under the radar?
Weyand: Yeah, so I mentioned I’m a pediatric hematologist, and I see a lot of adolescents and young women who have heavy menstrual bleeding, and that is one way that you can become quite anemic. So I see at—I work at a large academic medical center, so I see pretty severe cases but was thinking that if I’m seeing as many patients as I’m seeing with pretty severe anemia that there’s probably a lot of people out there that have less severe anemia that aren’t necessarily being identified.
Most of that is iron-deficiency anemia, which I think is a whole ’nother issue that is very undiagnosed and often dismissed. And iron deficiency—actually, a lot of people conflate iron deficiency with anemia, but they’re actually two different things. And iron deficiency, even when you’re not anemic, also matters and can cause a lot of symptoms and problems.
Feltman: Yeah, so how did you go about investigating that?
Weyand: Yeah, so we did a big study that [Centers for Disease Control and Prevention] has, kind of national study that they do called NHANES [National Health and Nutrition Examination Survey], where they collect data on kind of the general population and they get a lot of demographic data, medical history data; they get labs from them; and then it’s available to researchers to use for free.
And so we just took that database and looked at adolescents between 12 and 21 years of age that were female because a big risk factor for iron deficiency and anemia is menstruation ’cause that’s how you lose iron. And so we looked at that and kind of tried to weed out a number of patients who had other diseases or kind of other co-morbidities that would affect our prevalence to try to really get at what we would consider a healthy population to determine the rate of both iron deficiency and then also iron-deficiency anemia.
Feltman: Yeah. Well, what exactly has your research found?
Weyand: Yeah, so overall we found that about—it was 38.6 percent, so almost 40 percent of those 12- to 21-year-old females who were kind of otherwise healthy were iron-deficient ...
Feltman: Wow, yeah.
Weyand: And a smaller proportion, around 6 percent, were iron-deficient and anemic, because iron deficiency is kind of a spectrum, where you can be iron-deficient for quite some time and then kind of the severe end of iron deficiency, you become anemic.
Feltman: So how is it that doctors are, you know, so routinely missing these signs of iron deficiency and anemia in patients?
Weyand: I think it’s just really tough because the symptoms are so nonspecific, right? So if you think about other medical conditions: people talk about if you have chest pain, like, you’re having a heart attack, right? But a lot of the symptoms of iron deficiency and anemia are things like trouble sleeping—okay, well, there’s lots of causes for not sleeping well. Fatigue—there’s lots of reasons for people to be fatigued, especially in today’s day and age, where people are so busy and not necessarily getting adequate sleep or have time to exercise or eat healthy. So fatigue is—you know, can be caused by lots of things, and I think most of the people I see, even though I’m seeing adolescents, they’re all tired, right, so ...
Feltman: Mm-hmm.
Weyand: That doesn’t necessarily point you in a specific direction. Other things that it’s associated with, like depression and anxiety, are also really common and can be associated,or due to other things outside of iron deficiency.
It can also cause things like hair loss, which also, you know, people don’t necessarily have a good sense of, like, how much hair you should be losing. Or even, like, fatigue—like, how do we rate fatigue? Like, if you talk to a lot of people, they’re like, “Yeah, I’m tired,” but when is it actually a problem versus just, “Okay, maybe you need to, like, sleep a little later on the weekend”?
Feltman: Yeah. I understand that anemia or iron deficiency were more prevalent in certain groups; is that correct?
Weyand: Yes, that’s correct. So the most affected kind of worldwide are women of reproductive age, or, you know, people who menstruate or can get pregnant, as well as kind of toddlers is another kind of age group where it can be more prevalent as well.
Feltman: And what are sort of the, the main takeaways...[full transcript]
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