译者：有些事，你不经历，不可能深有体会。如果没有过“感觉累”的那一段时光，我也许不会看这篇文章。（不想听我唠叨的，跳过下面的故事。）

我的Covid疫苗卡显示，第三针疫苗是2021年12月8日接种的。记忆力不佳的我，依然能够清清楚楚地记得那一天的事，因为它非同一般。打完疫苗，在Kaiser的休息室呆够n分钟，我去Nijiya market买食品。看到一瓶胖乎乎的生蚝被促销，我买回家用韩国泡菜煮生蚝汤。吃着吃着，感觉不妙（恶心）。以前的两针疫苗，也有反应，尤其是几个小时后；有时第二天依然感觉有低烧。每次都是一个星期后才恢复正常；但是，从来没有影响到食欲。这一次，换了Moderna的（因为专家建议混搭），反应非常不好（我现在依然对生蚝没有兴趣）。一个星期后，应该是“康复”了；但是，我依然感觉累。前所未有的懒：淋浴好像是一种负担。当时，我也没有觉得哪里不对。对自己说：年龄大了，也许就是这种感觉。（但是，许多人一直工作到70岁。难道他们不累？）【注：我不怀疑疫苗的有效。我后来又打了Covid疫苗。还打了带状疱疹疫苗，虽然第一针非常痛；不是我一个人的抱怨。最近一次的Covid疫苗，和流感疫苗一起打，一边一针。错误的选择：晚上不知道睡哪边才不疼。LOL】

一直到2022年初，闺蜜极力推荐BioAstin（虾青素）。这是夏威夷出产的，在Costco常常有促销；我拿了一瓶（12 mg一粒），一天一粒。约3天后，明显感觉自己睡眠质量提高了（睡得非常非常沉），不再感觉累。从此以后，我“迷上了”虾青素。【注：我不是保健品推销员。】当然，我害怕“上瘾”。吃一阵子，停了。然后，感觉有点累，又开始吃。断断续续地持续了将近两年，直到我迷上了“轻呼吸”。

https://blog.sciencenet.cn/blog-306792-1411644.html

不久，我放弃了虾青素。

故事本该到此为止。但是，几天前，我又开始吃虾青素（这次是4  mg一粒）。原因非常简单：我发现晚上不困。（不是因为我感觉累。）如果我取消每天上午的一杯咖啡（其咖啡因约为买的一杯咖啡的一半），我担心下午会困。正好师妹说她吃虾青素有助于睡眠，我也不想浪费冰箱里的虾青素，就开吃。效果出奇的好：睡眠改善了。【注：我推荐朋友吃。有些朋友说：没有感觉。】

 好了，言归正传。

为什么有的人总是感觉累？

对于一些人来说，无论他们睡了多少小时，他们仍然感到疲倦和精力不足。 为什么？

大多数时候，我都坚持有规律地生活，尤其是在睡眠方面。 在开始感到疲倦之前，我就做好了上床睡觉的准备：换上睡衣，刷牙，并进行过于复杂的皮肤护理程序。 我把手机留在餐厅里，然后回到卧室——一间安静、灯光昏暗、温度适宜的卧室——在我的感恩日记中简短地记录（这一天）。 接下来是半小时的小说阅读，然后在晚上 11 点左右关灯。

八个半小时后，我的闹钟响了，我醒来时感觉……很累。 我正值早期的中年，经常锻炼身体，而且据我所知，我很健康（敲一下木头）。 【译者注：敲一下木头是为了“辟邪“， 一种迷信的举止。】那么，为什么尽管睡眠充足，大多数早晨我还是无法保持“精力充沛”呢？【Why, then, does being bright-eyed and bushy-tailed elude me most mornings, despite sufficient sleep?】

事实证明我并不是唯一有这种感觉的。 根据 2023 年对三大洲 91 项研究进行的大数据分析，全球每 5 名成年人中就有 1 人经历过持续长达 6 个月的全身疲劳，尽管没有任何潜在的健康状况。 在美国，国家睡眠基金会 2019 年对 1000 多名成年人进行的调查显示，44% 的人表示，他们每周有2～4天感到困倦。 2022 年 YouGov 对近 1,700 人进行的一项民意调查发现，八分之一的英国成年人“一直”感到疲倦，另外四分之一的人“大部分时间”都疲惫不堪。 女性比男性更容易感到疲劳，无论她们是否有孩子——这一发现在多项研究中出现。

一个模糊的概念

在苏格兰阿伯丁执业十多年的家庭医生罗莎琳德·亚当（Rosalind Adam）表示，疲劳是患者“非常非常普遍”的抱怨。 这种情况如此频繁，以至于国家医疗服务体系甚至有自己的缩写：TATT（Tired All The Time；一直疲倦）。

尽管如此普遍，科学家们对疲劳的理解——它的原因、它如何改变我们的身体和大脑，以及如何最好地治疗它——却非常有限。 即使确定一个定义也是很棘手的。 亚当解释说，疲劳与困倦不同，后者“更多的是入睡的倾向”。 “当然，这两者是相互关联的，但疲劳是多维的，”她说。

西雅图华盛顿大学组织行为与管理学教授克里斯托弗·巴恩斯（Christopher Barnes）研究睡眠不足如何影响工作场所，他说：“这是一种包罗万象的感觉疲倦的概念。” “有很多方式会让我们感到疲倦。”

例如，在长途徒步旅行或在健身房进行特别剧烈的锻炼后，你可能会感到身体疲劳。 “这是正常的生理疲劳，”马里兰州贝塞斯达国立卫生研究院的项目主任维基·惠特莫尔（Vicky Whittemore）解释道，她研究疲劳的生物学。 “这很容易理解，人们长期以来一直在研究肌肉疲劳。”

但疲劳还包括认知和情感方面——这解释了为什么当我们疲倦时，我们可能会出现脑雾，发现做事很困难，或者对周围的人发脾气。 惠特莫尔说，直到过去十年，由于成像技术和生化检测的进步使我们能够研究大脑的实时变化，科学家们才能够更深入地研究疲劳的其他方面。 “我们现在才刚刚开始了解神经生物学以及大脑的哪些部分正在感知疲劳。”

另一个挑战是，疲劳是非常主观的，并且可能因多种原因而出现。 它是许多疾病和慢性病的症状，包括癌症、多发性硬化症、长期新冠肺炎、抑郁症、和肌痛性脑脊髓炎。 然而，它也可能有不太严重的原因。 “区分疾病和非疾病相关的疲劳是绝对重要的，”亚当说，她也在阿伯丁大学任教，她正在领导一项正在进行的研究，研究疲劳如何影响骨髓瘤、心力衰竭和长期新冠患者 。

“我认为，如果我们能够消除不同类型的疲劳，我们也许能够以不同的方式对待它们并提供更量身定制的解决方案，”亚当说。

质量、而不是数量

我们一再称赞充足睡眠的好处：成年人需要的睡眠时间各不相同，但大多数人每晚需要七小时或更长；专家建议睡眠时间在7～9小时之间。 如果没有这段休息时间，我们的身体将无法修复肌肉、增强免疫力、调节情绪、巩固记忆和新信息、以及其他关键功能。 长时间疲劳的人比一般人群死亡的风险更高，焦虑和抑郁的风险也更高。

日常生活中，休息不足会导致头痛和其他身体疼痛，还会导致烦躁、情绪低落和精神不集中。 这些影响往往会蔓延到我们的人际关系中。 巴恩斯说：“我们从有关睡眠和婚姻满意度的文献中得知，当婚姻中的一个人睡眠不足时，这对夫妇之间就会出现更多的冲突。”

疲劳还会对工作场所产生不利影响，对绩效和领导力产生影响。 巴恩斯是第一个研究睡眠不足的老板更有可能通过敌意的言语和非言语行为虐待员工的人：“他们上班时的自控力较差，而且更有可能从事我们所说的‘ 滥用监督’，”他说。 （阅读 BBC Future 的更多内容，了解职业倦怠发生的原因以及应对措施。）

更糟糕的是，疲劳可能会带来毁灭性的后果——在英国，疲劳是主要道路上 20% 的事故的根本原因。 与疲劳或睡眠不足相关的人为错误以及其他因素，也与许多人为灾难有关，包括挑战者号航天飞机事故和埃克森·瓦尔迪兹漏油事件。 工业与系统工程教授兰贾纳·梅塔 (Ranjana Mehta) 表示：“无论是陆上还是海上，石油和天然气 [开采] 的疲劳已经导致了重大灾难、人员伤亡、经济问题和环境问题，而这些问题仍然困扰着我们。” 他在威斯康星大学麦迪逊分校研究职业疲劳。

但充足的睡眠只是其中的一部分。睡眠质量也很重要，甚至更重要。 “深沉睡眠时间即使少，也比时间长但常常中断的睡眠要好，”惠特莫尔说。 “如果你中断了睡眠，你会感觉精神不振。”

部分原因是当我们睡觉时，我们的大脑会关闭那些无关的“活动”。 静止的神经元为脑脊液（通常围绕着大脑）创造空间，会涌入（大脑）并清除（大脑中）积累的碎片，例如通常与阿尔茨海默病相关的粘性β-淀粉样斑块。 这是一种科学家称之为类淋巴系统的废物清除系统。 “如果你的睡眠受到干扰或功能失调，就会破坏整个平衡，”惠特莫尔说。 “导致没有那么多毒素从你的大脑中被清除。”

有趣的是，我们的类淋巴系统每天在同一时间工作得最好，上海纽约大学睡眠心理学家兼研究助理教授 Daniel Jin Blum 说。 “因此，如果你在正常时间获得相同时间的深度睡眠与换一个八小时（非正常时间）的深度睡眠时间相同，那么排除毒素的能力就会受到显着影响。”

这意味着我们什么时候睡觉很重要。 将睡眠与我们的自然昼夜节律（大脑的 24 小时内部时钟，调节警觉和困倦的周期）同步，可以带来最佳质量的休息。 这就解释了为什么轮班工作常常与不良的健康结果相关，从烧胃（胃酸过多）到糖尿病。

“除此之外，如果你得到同样的八小时睡眠，但不是在正常的昼夜节律期间，你几乎没有快速眼动睡眠，你并没有真正获得好处，”布鲁姆说，指的是第四个也是最后一个阶段 我们的睡眠周期的特点是快速的眼球运动，我们通常会在这个过程中做梦、加强神经连接并处理白天的情绪。 快速眼动睡眠太少或失调与抑郁症、痴呆症、帕金森病、和其他认知问题有关。

无数的原因

鉴于睡眠质量差对我们的健康、人际关系和工作造成普遍影响，尝试找出所有这些痛苦的根源非常重要。 当病人抱怨持续疲劳时，亚当做的第一件事就是排除任何医疗健康原因。

血液检查有时有助于查明甲状腺疾病或雌激素和其他激素的不平衡，这些情况通常与疲劳感有关，尤其是女性。

测试还可以揭示你是否缺乏某些营养素，例如维生素 B12、叶酸和 D； 或铁和镁等矿物质。 “营养缺乏在导致疲劳方面发挥着重要作用，”挪威非营利组织营养与环境医学委员会的创始人盖尔·比约克伦德 (Geir Bjørklund) 说。 “必需营养素，包括维生素、矿物质和膳食成分，对于包括能量代谢在内的各种生理过程至关重要，”他说。

但血液测试只能到此为止。 亚当说：“我们在初级保健中看到的 90% 的病例中，它们都表现正常，这就是为什么获取全面的临床病史至关重要”。

“对于健康的个体，我们着眼于运动、睡眠、饮食、心理健康等因素的影响。这实际上是关注个体以及对他们可能重要的因素，”亚当说。 例如，一个人如果有年幼的孩子们），这可能会使他们不间断的睡眠成为一种遥远的奢侈。

尤其是压力，是导致疲劳的一个重要因素。 引人注目的是，2022 年对中国 16,200 多名政府雇员进行的一项研究发现，那些在基线时经历过负面压力生活事件的人，在后续报告中感到疲劳的可能性是其他人的两倍。

当我们感到压力时，我们的身体会产生一种叫做皮质醇的激素（cortisol），它反过来会提高我们的体温和心率，使我们做好应对威胁的准备。 皮质醇水平全天自然波动，但当它持续升高时，你就更难入睡和保持睡眠状态。 惠特莫尔说，这就是那种“疲惫但紧张”的感觉。

布鲁姆说，健康人疲劳的另一个真正常见原因是睡眠障碍或呼吸问题。

这包括打鼾；当气道部分或完全阻塞时就会发生打鼾。 他说：“所有打鼾都是不正常的，可能是睡眠呼吸暂停的征兆。”睡眠呼吸暂停会导致一些睡眠者在整个晚上反复停止和开始呼吸。

布鲁姆说，所有这些都会扰乱自然睡眠模式，使深度睡眠变得难以捉摸。 “所以人们即使得到了7～9小时的睡眠，但质量不够。”

脱水是疲劳的另一个主要原因。 其他典型的罪魁祸首包括咖啡因和酒精。 “我认为大多数人都低估了它们对睡眠质量的影响，”他说。 “例如，咖啡因的半衰期约为五个小时，这意味着即使你在中午喝了一杯咖啡，四分之一的咖啡因也会在午夜残留下来。”

酒精，尤其是临睡前的酒精，还会以多种方式对睡眠质量产生负面影响：加剧呼吸问题、扰乱昼夜节律、阻碍快速眼动睡眠。 “通常情况下，在第一个睡眠周期中，你入睡的速度可能会更快一些，并且睡眠会更深入一些，”布鲁姆解释道。 “但在那之后，它只是让我们在最浅的睡眠阶段反弹，导致更多的觉醒和额外的皮质醇在一夜之间飙升。”

归根结底，比约克伦德解释说，增强能量的秘诀大多是我们理性思维已经知道的：“采用均衡饮食，解决营养缺乏问题，保持良好的睡眠卫生，通过正念（冥想）等技术管理压力，定期参加体育锻炼。 活动，确保适当的水分，考虑认知行为疗法等治疗干预，并建立支持群体。”

当然，如何（真正有效地）实施这些技术完全是另一回事。 看来我需要重新调整我的“日常生活规律”。（Implementing those techniques, of course, is another matter entirely. It looks like a rework of my routine is in order.）

Why do some people feel tired all the time?

25th January 2024, 04:00 HST

By Sandy Ong Features correspondent

https://www.bbc.com/future/article/20240125-why-do-some-people-feel-tired-all-the-time

For some people, no matter how much sleep they get, they still feel tired and low in energy. Why?

On most days, I'm a stickler for routine, especially when it comes to sleep. I get ready for bed well before I begin to feel tired: changing into my pyjamas, cleaning my teeth, and doing an overly elaborate skin care routine. I leave my phone in the dining room where it stays overnight, then retire to my bedroom – one that's quiet, dimly-lit, and of perfect Goldilocks temperature – to scribble briefly in my gratitude journal. A half-hour of fiction reading follows, before turning the lights out at roughly 11pm.

Eight-and-a-half hours later, my alarm rings and I wake up feeling…tired. I am early mid-life, exercise regularly, and am, as far as I know, healthy (knock on wood). Why, then, does being bright-eyed and bushy-tailed elude me most mornings, despite sufficient sleep?

It turns out I'm far from alone. According to a 2023 meta-analysis that examined 91 studies across three continents, one in every five adults worldwide experienced general fatigue lasting up to six months, despite having no underlying medical conditions. In the US, 44% of the more than 1,000 adults surveyed by the National Sleep Foundation in 2019 said they felt sleepy between two to four days every week. While a 2022 YouGov poll of nearly 1,700 people found that one in eight UK adultswere tired "all the time", with another quarter knackered "most of the time". Women were more likely to be fatigued than men, regardless of whether they had children or not — a finding that was echoed across multiple studies.

A fuzzy concept

Tiredness is "a very, very common" complaint among the patients, says Rosalind Adam, a family physician who has been practising in Aberdeen, Scotland, for more than a decade. The condition is so frequent that the National Health Service even has its own acronym for it: TATT (Tired All The Time).

But for all this ubiquity, scientists' understanding of fatigue – what causes it, how it changes our bodies and brains, as well as how best to treat it – is incredibly limited. Even pinning down a definition has been tricky. Tiredness is different from sleepiness, which is "more a propensity to fall asleep", explains Adam. "The two are interrelated, of course, but fatigue is much more multidimensional," she says.

"It's sort of a catch-all concept of feeling tired," says Christopher Barnes, professor of organisational behaviour and management at the University of Washington in Seattle, who studies how sleep deprivation affects the workplace. "And there's lots of ways that we can feel tired."

There's physical fatigue, for instance, the kind you might feel after a long hike or a particularly strenuous session in the gym. "That's normal physiological fatigue," explains Vicky Whittemore, a program director at the National Institutes of Health in Bethesda, Maryland, who studies the biology of fatigue. "It's easy to understand and people have been studying muscle fatigue for a long time."

But fatigue can also encompass a cognitive and emotional aspect – which explains why when we're tired, we might experience brain fog, find it a slog to get things done, or snap at those around us. It's only in the past decade that scientists have been able to dig deeper into these other facets of fatigue, thanks to advances in imaging technology and biochemical assays that allow us to study real-time changes in the brain, says Whittemore. "We're really just beginning to understand the neurobiology now and what parts of the brain are perceiving fatigue."

Another challenge is that fatigue is incredibly subjective, and it can arise for myriad reasons. It's a symptom of many diseases and chronic conditions, including cancer, multiple sclerosis, long Covid, depression, and myalgic encephalomyelitis. However, it can also have much less serious causes. "It's absolutely important to distinguish between illness and non-illness-related tiredness," says Adam, who also teaches at the University of Aberdeen, where she is leading an ongoing study examining how fatigue impacts individuals with myeloma, heart failure, and long Covid.

"I think if we can unpick different types of fatigue, we might be able to treat them differently and offer more tailored solutions," says Adam.

Quality over quantity

The benefits of getting sufficient sleep – the amount that adults need varies, but most people need seven or more hours a night, and experts recommend getting between seven and nine hours – have been extolled upon us time and again. Without this downtime, our bodies wouldn't be able to repair muscles, boost immunity, regulate emotions, consolidate memories and new information, among other critical functions. People who are fatigued for prolonged periods have a higher risk of death than the general population, as well as a higher risk of anxiety and depression.

On a daily basis, getting inadequate rest can result in headaches and other bodily pains, as well as cause feelings of irritability, low mood, and an unfocused mental state. These effects often spill over to our relationships. "We know from the literature on sleep and marital satisfaction that when one person in a marriage is sleep deprived, there's more conflict in that couple," says Barnes.

Fatigue can also adversely affect the workplace, with repercussions on both performance and leadership. Barnes was the first to examine how sleep-deprived bosses are more likely to mistreat their employees through hostile verbal and non-verbal behaviour: "They go into work with less self-control and they're more likely to engage in what we call ‘abusive supervision'," he says. (Read more from BBC Future about why burnout happens and what to do about it.)

Worse still, fatigue can have devastating outcomes — in the UK, tiredness is the root cause of 20% of all accidents on major roads. Human error linked to fatigue or sleep loss has also been implicated, along with other factors, in numerous man-made disasters, including the Challenger Space Shuttle accident and the Exxon Valdez oil spill. "Fatigue in oil and gas [extraction], both onshore and offshore, has resulted in significant catastrophes, the loss of lives, economic issues, and environmental issues that we still suffer from," says Ranjana Mehta, a professor of industrial and systems engineering at the University of Wisconsin-Madison, Madison, who studies occupational fatigue.

But getting sufficient shuteye is only one part of the equation. Quality matters too, if not more. "Getting fewer hours of solid sleep is better than more hours of sleep, but interrupted sleep," says Whittemore. "You feel much less refreshed if you have interrupted sleep."

That's partly because when we sleep, our brains power down extraneous processes. The resting neurons create space for cerebrospinal fluid, which usually surrounds the brain, to flood in and clear out accumulated debris, such as the sticky beta-amyloid plaques that are usually associated with Alzheimer's disease. It's a sort of waste-clearance system scientists call the glymphatic system. "If you have disrupted or dysfunctional sleep, it disrupts that whole balance," says Whittemore. "So there aren't as many toxins being cleared from your brain."

Interestingly, our glymphatic systems work best at the same time every day, says Daniel Jin Blum, a sleep psychologist and research assistant professor at New York University Shanghai. "So if you get the same amount of deep sleep at your regular time versus shifted eight hours later, the ability to flush out toxins is significantly compromised."

This means that when we get our shuteye is important. Syncing sleep with our natural circadian rhythms – the brain's 24-hour internal clock that regulates the cycle of alertness and sleepiness – gives rise to the best-quality rest. This explains why shift work is often associated with poor health outcomes, ranging from heartburn to diabetes.

"Among other things, if you get that same eight hours of sleep, but not during the regular circadian period, you get almost no REM sleep and you're not really reaping the benefits," says Blum, referring to the fourth and final stage of our sleep cycle that's characterised by rapid eye movements, where we typically dream, strengthen neural connections, and process emotions from the day. Too little or dysregulated REM sleep has been linked with depression, dementia, Parkinson's disease, and other cognitive issues.

Myriad reasons

Given the pervasive effects of poor-quality sleep on our health, relationships, and work, it's important to try and unearth the root of all this misery. When patients complain of persistent fatigue, the first thing Adam does is rule out any medical causes.

Blood tests can sometimes be useful in pinpointing thyroid disorders or an imbalance of oestrogen and other hormones – conditions that are frequently linked with feelings of fatigue, especially in women.

Tests can also reveal if you're lacking certain nutrients like vitamin B12, folate, and D; or minerals such as iron and magnesium. "Nutrient deficiency plays a substantial role in contributing to fatigue," says Geir Bjørklund, who founded the Norwegian nonprofit Council for Nutritional and Environmental Medicine. "Essential nutrients, including vitamins, minerals, and dietary components, are crucial for various physiological processes, including energy metabolism," he says.

But blood tests only go so far. "They show up normal in 90% of the cases we see in primary care," says Adam, "which is why taking a comprehensive clinical history is key".

"In healthy individuals, we look at contributing roles of things like exercise, sleep, diet, mental health. It's really about looking at that individual and the factors that might be important to them," says Adam. For instance, a person may have young children, which may make uninterrupted sleep a far-off luxury.

Stress, in particular, is a big contributor to fatigue. Tellingly, a 2022 study of more than 16,200 government employees in China found that those who experienced negative stressful life events at baseline were twice as likely to report feeling fatigued at follow-up.

When we're stressed, our bodies produce a hormone called cortisol, which in turn raises our body temperature and heart rate to gear us up to face a threat. Cortisol levels fluctuate naturally throughout the day, but when they remain elevated, it's harder to fall asleep and stay asleep. It's that "tired but wired" feeling, says Whittemore.

Another really common cause of fatigue in otherwise healthy people is sleep disorders or breathing issues, says Blum.

This includes snoring, which occurs when one's airway is partially or fully blocked. "All snoring is abnormal, and may be a sign of sleep apnoea," he says, referring to the disorder that causes some sleepers to stop and start breathing repeatedly throughout the night.

All this can disrupt natural sleep patterns and make deep sleep elusive, says Blum. "So people get that seven to nine hours of sleep, but it's insufficient quality."

Dehydration is another major cause of fatigue. Other typical culprits include caffeine and alcohol. "I think most people underestimate how much they impact the quality of their sleep," he says. "Caffeine, for instance, has a half-life of roughly five hours, which means even when you have a cup of coffee at noon, a quarter of that caffeine will remain at midnight."

Alcohol, especially close to bedtime, can also negatively affect sleep quality in many ways: aggravating breathing problems, disrupting the circadian cycle, and blocking REM sleep. "Oftentimes you will fall asleep maybe a little faster during that first sleep cycle and get a little more deep-sleep," explains Blum. "But after that, it just kind of bounces us around our lightest stage of sleep, causing more awakening and additional cortisol spikes overnight."

At the end of the day, Bjørklund explains that the tips for boosting energy are mostly what our rational minds already know: "Embrace a balanced diet, address nutrient deficiencies, maintain good sleep hygiene, manage stress through techniques like mindfulness, engage in regular physical activity, ensure proper hydration, consider therapeutic interventional like cognitive behaviour therapy, and build a support network."

Implementing those techniques, of course, is another matter entirely. It looks like a rework of my routine is in order.