一杯咖啡，比熬夜更伤脑？Nature子刊：熟睡时，咖啡因仍在扰乱脑电波，“偷走”深度睡眠修复力；且还搅动激素平衡，引爆代谢危机Is a cup of coffee more brain damaging than staying up late? Nature Journal: Caffeine still disrupts brain waves during deep sleep, stealing the ability to repair deep sleep; And it also disrupts hormone balance, triggering metabolic crisis

每个工作日的下午，总有一种神奇的「催睡魔力」。大脑像是生了锈，无论怎么使劲都转不动。强打精神想认真搬砖，却偏偏心有余而力不足，思绪早就不知道飘到哪里去了。再看看堆积如山的工作，安心「摸鱼」的念头也顿时消散了一大半。

于是，「牛马」们也别无他法。反正「磨刀不误砍柴工」，不如喝杯咖啡再接着开工。不得不说，这招很多时候确实管用。咖啡下肚，昏昏沉沉的脑袋很快又「盘活」了，原本卡住的思路也慢慢接了回来。

一杯咖啡下肚，睡眠「遭殃」

大脑连夜进入「工作模式」

可咖啡因把人从下午的困倦里「拽」出来之后，这股「精神劲儿」会随着夜幕降临而消失吗？

来自蒙特利尔大学等机构的研究团队发表于Communications Biology的一项研究[1]就发现，「炫」完咖啡后，即使已进入睡眠状态，大脑也没有完全安静下来。相反，脑电信号的复杂度和活跃度明显提高，大脑表现出一种更接近清醒状态的信息处理模式，削弱了深睡眠原本应该承担的修复作用。

夜间睡眠期间，研究者用脑电图全程记录了志愿者的脑电信号，随后将数据划分为非快速眼动睡眠（NREM，深度睡眠期）和快速眼动睡眠（REM，梦境多发阶段）。

数据收集完成后，他们又计算了样本熵和Lempel-Ziv复杂度（LZc）这两项核心指标。样本熵主要衡量脑电信号的「不可预测性」，信号越复杂、越不规则，熵值就越高。LZc评估信号中包含的「新信息」量，信号越丰富、越少重复，复杂度也越高。

结果显示，摄入咖啡因之后，样本熵和LZc这两项指标都出现了显著攀升。这也意味着，就算人已经睡熟了，大脑的脑电信号依然比正常情况下更复杂和活跃。

不仅如此，咖啡因在让大脑变「热闹」的同时，还在推动它向「临界态」的方向偏移。

通俗点说，「临界态」是大脑介于过度沉寂和过度混乱之间的那个「最佳工作区间」。当然，对需要集中精力，迅速作出反应的白天来说，大脑处于「临界态」是好事。此时的大脑既能灵活应对外界变化，又不会因为过度兴奋而陷入无序，信息处理效率最高。

可「甲之蜜糖，乙之砒霜」，到了晚上，接受了咖啡因「洗礼」的大脑却没有没有安安稳稳地休息，向着「临界态」靠拢，仍维持着一种本该属于白天的活跃状态。

研究者还用了「DFA标度指数」和「脑电1/f非周期活动斜率」这两个指标来验证这一判断。前者衡量大脑信号在时间上的持久性，指数越高，信号越拖沓、越不愿意切换状态；指数降低，则意味着信号变得更灵活。后者反映脑电背景噪声的陡峭程度，斜率越平缓，大脑的兴奋性就越高。

而这两个指标在咖啡因作用下都出现了显著下降。可见，咖啡因正在把睡眠中的大脑从深度休息时对外界「爱答不理」的状态，推向一个更加兴奋、灵活、随时准备响应的模式。

不过，咖啡因对不同年龄的人影响也不一样。尤其到了REM睡眠阶段，咖啡因对年轻人大脑的影响要显著强于中年人。

研究者又比较了两组人在没有摄入咖啡因，只服用安慰剂的情况下，原本的脑电状态。结果发现，中年人的脑电本身就已经呈现出更高的复杂度、更低的DFA标度指数，以及更平缓的1/f斜率。但年轻人摄入咖啡因之后，才出现相似的变化。

所以研究者推测，随着年龄增长，大脑在自然老化的过程中，提前「模拟」了咖啡因的作用，逐渐形成了一种类似咖啡因作用后的活动模式。既然大脑本身就已经处在这样一种状态中，咖啡因再来推一把，能推的余地自然就小了。

那咖啡因为何会让睡眠「崩坏」呢？

研究者指出，咖啡因直接的作用对象，其实是大脑里的「困意信号」腺苷。白天清醒的时间越长，腺苷就会一点点积累，让大脑逐渐感到疲惫，到了晚上，困意也就越来越强。可咖啡因一来，就先「抢占」了腺苷原本要结合的受体，让这种「该睡觉了」的信号暂时传不过去。于是，人喝完咖啡后不容易犯困，到了晚上，大脑也可能还维持着一股清醒劲儿。

并且，咖啡因还会牵动大脑里多套神经递质系统，影响多巴胺、去甲肾上腺素和乙酰胆碱等物质的活动，同时干扰GABA和谷氨酸之间的平衡。深睡眠阶段本该是大脑抑制活动占主导的黄金时间，大脑安静下来，才能好好清理代谢废物、巩固白天的记忆。咖啡因这一通操作，把本该沉寂下来的大脑重新「拽」回了一个更兴奋的状态。

咖啡因，或搅乱激素平衡

事实上，摄入咖啡因之后的麻烦，还不止影响睡眠这一桩。

一项发表于Frontiers in Nutrition的研究利用美国国家健康与营养调查（NHANES）的数据，分析了咖啡因代谢与性激素水平之间的关系。研究团队发现，咖啡因竟还牵动着体内性激素的平衡。

具体而言，PC2所代表的咖啡因代谢通路与男性雌二醇（E2）水平呈显著负相关。对男性来说，E2参与骨密度和心血管功能的调节，水平过低可能增加骨折以及心血管问题的风险。

而把男性和女性放在一起分析后，咖啡因代谢产物整体与性激素结合球蛋白（SHBG）和总睾酮（TT）呈显著负相关。SHBG水平下降可能进一步改变血液中睾酮和E2的可利用状态；TT水平降低，可能影响男性的肌肉量和性功能，对女性则可能牵动骨骼健康和整体代谢。

总体而言，上述研究揭示了，摄入咖啡因或显著提升睡眠中大脑的复杂度和活跃度，将其推向一种本该属于白天的「临界态」高效运作模式，削弱了深度睡眠应有的修复功能，且这种干扰在年轻人身上表现得更加明显。不仅如此，咖啡因代谢产物还会在暗中搅动激素平衡，在骨密度、心血管健康、及肌肉量等方面埋下隐患。

巴尔扎克曾说，咖啡在他的生活中举足轻重，其作用可以史诗级来论之。对如今忙碌的「牛马」们来说，这话一点都不夸张。想要把工作效率拉满，扛过工作日下午的困意，一杯咖啡确实是不二之选。但要是我们发现自个儿喝完咖啡之后，晚上容易翻来覆去睡不踏实，第二天醒来脑子还是像蒙了一层雾，那这杯「续命水」就得重新掂量掂量了。

注：研究[1]样本量有限，且200mg咖啡因摄入为急性干预，不能直接等同于长期慢性咖啡因摄入；研究[2]基于横断面分析，无法直接推断因果关系。

参考资料：

[1]Thölke, P., Arcand‑Lavigne, M., Lajnef, T., Frenette, S., Carrier, J., &Jerbi, K. (2025). Caffeine induces age‑dependent increases in brain complexity and criticality during sleep. Communications Biology, 8(1), 685.

[2]Zhou J, Qin L. Associations of urinary caffeine metabolites with sex hormones: comparison of three statistical models[J]. Frontiers in Nutrition, 2025, 11:1497483.撰文 | 木白

编辑 | 木白

Every weekday afternoon, there is always a magical 'sleep inducing magic'. The brain seems to have rusted, no matter how hard you try, it can't move. I tried my best to move the bricks seriously, but unfortunately, my heart was full of energy but my strength was insufficient. My thoughts had already drifted somewhere. Looking at the pile of work, the thought of "slacking off" with peace of mind dissipated halfway.

So, the 'cows and horses' had no other choice. Anyway, as the saying goes, 'sharpening a knife doesn't make a mistake for chopping wood.' It's better to have a cup of coffee before resuming work. It has to be said that this trick often works. After drinking coffee, the drowsy mind quickly regained its vitality, and the previously stuck train of thought slowly came back in.

A cup of coffee, sleep 'suffers'

Brain enters' working mode 'overnight

After caffeine pulls people out of the afternoon drowsiness, will this "mental energy" disappear as night falls?

A research team from the University of Montreal and other institutions published a study in Communications Biology [1] that found that after "showing off" coffee, even if the brain has entered a sleep state, it has not completely calmed down. On the contrary, the complexity and activity of EEG signals have significantly increased, and the brain exhibits an information processing mode closer to wakefulness, weakening the repair function that deep sleep should have undertaken.

During nighttime sleep, researchers recorded the volunteers' EEG signals using electroencephalography, and then divided the data into non rapid eye movement sleep (NREM, deep sleep phase) and rapid eye movement sleep (REM, dream phase).

After the data collection was completed, they calculated two core metrics, sample entropy and Lempel Ziv complexity (LZc). Sample entropy mainly measures the "unpredictability" of EEG signals. The more complex and irregular the signal, the higher the entropy value. LZc evaluates the amount of "new information" contained in the signal, and the richer and less repetitive the signal, the higher the complexity.

The results showed that after consuming caffeine, both sample entropy and LZc indicators showed significant increases. This also means that even if a person is already asleep, the brain's electrical signals are still more complex and active than normal.

Not only that, caffeine not only makes the brain "lively", but also pushes it towards the "critical state" direction.

Simply put, the "critical state" is the "optimal working range" of the brain between excessive silence and excessive chaos. Of course, for daytime activities that require concentration and quick response, the brain being in a "critical state" is a good thing. At this point, the brain is able to flexibly respond to external changes without getting too excited and falling into disorder, resulting in the highest efficiency of information processing.

The honey of A, the arsenic of B ", at night, the brain that has been" baptized "with caffeine does not rest steadily, approaching the" critical state "and still maintaining an active state that should belong to the daytime.

The researchers also used two indicators, the "DFA scaling index" and the "EEG 1/f non periodic activity slope," to verify this judgment. The former measures the persistence of brain signals over time, with higher indices indicating more sluggish signals and less willingness to switch states; If the index decreases, it means that the signal becomes more flexible. The latter reflects the steepness of EEG background noise, with a flatter slope indicating higher brain excitability.

And both indicators showed a significant decrease under the action of caffeine. It can be seen that caffeine is pushing the sleeping brain from a state of "unresponsive" to the outside world during deep rest to a more excited, flexible, and ready to respond mode.

However, caffeine has different effects on people of different ages. Especially during REM sleep, caffeine has a significantly stronger impact on the brain of young people than middle-aged people.

The researchers compared the original EEG states of two groups of people who did not consume caffeine and only took a placebo. As a result, it was found that the EEG of middle-aged individuals already exhibited higher complexity, lower DFA scaling index, and smoother 1/f slope. But similar changes only occur after young people consume caffeine.

So researchers speculate that as age increases, the brain "simulates" the effects of caffeine in advance during natural aging, gradually forming an activity pattern similar to that of caffeine. Since the brain itself is already in such a state, if caffeine is pushed again, there is naturally less room for it to be pushed.

Why does caffeine disrupt sleep?

Researchers point out that the direct target of caffeine is actually adenosine, the "drowsiness signal" in the brain. The longer you stay awake during the day, the more adenosine accumulates, causing the brain to gradually feel tired. At night, the drowsiness becomes stronger. But when caffeine comes, it first "seizes" the receptors that adenosine was supposed to bind to, temporarily preventing the signal that "it's time to sleep" from being transmitted. So, after drinking coffee, people are less likely to feel sleepy, and at night, their brains may still maintain a sense of clarity.

Moreover, caffeine can also affect multiple neurotransmitter systems in the brain, affecting the activity of substances such as dopamine, norepinephrine, and acetylcholine, while disrupting the balance between GABA and glutamate. The deep sleep stage should be the golden time when brain inhibitory activity dominates. Only when the brain quiets down can it properly clear metabolic waste and consolidate daytime memories. The action of caffeine pulls the brain, which should have been dormant, back to a more excited state.

Caffeine, or disrupting hormone balance

In fact, the trouble of consuming caffeine is not just affecting sleep.

A study published in Frontiers in Nutrition analyzed the relationship between caffeine metabolism and sex hormone levels using data from the National Health and Nutrition Examination Survey (NHANES) in the United States. The research team found that caffeine actually affects the balance of sex hormones in the body.

Specifically, the caffeine metabolism pathway represented by PC2 is significantly negatively correlated with male estradiol (E2) levels. For men, E2 is involved in regulating bone density and cardiovascular function, and low levels may increase the risk of fractures and cardiovascular problems.

After analyzing both males and females together, the overall caffeine metabolites showed a significant negative correlation with sex hormone binding globulin (SHBG) and total testosterone (TT). The decrease in SHBG levels may further alter the availability of testosterone and E2 in the blood; A decrease in TT levels may affect male muscle mass and sexual function, while for females it may affect bone health and overall metabolism.

Overall, the above research reveals that consuming caffeine significantly increases the complexity and activity of the brain during sleep, pushing it towards a highly efficient operating mode that should belong to the "critical state" of the daytime, weakening the repair function that deep sleep should have, and this interference is more pronounced in young people. Not only that, caffeine metabolites can also secretly disrupt hormone balance, laying hidden dangers in bone density, cardiovascular health, and muscle mass.

Balzac once said that coffee played a crucial role in his life, and its significance can be discussed on an epic scale. For the busy "cattle and horses" nowadays, this statement is not exaggerated at all. To maximize work efficiency and overcome the drowsiness of weekday afternoons, a cup of coffee is indeed the best choice. But if we find that after drinking coffee, we tend to toss and turn at night and can't sleep soundly, and wake up the next day with a layer of fog in our minds, then this cup of "life-saving water" needs to be re evaluated.

Note: The sample size of study [1] is limited, and 200mg caffeine intake is an acute intervention and cannot be directly equated with long-term chronic caffeine intake; Research [2] is based on cross-sectional analysis and cannot directly infer causal relationships.

reference material:

[1]Thö lke, P., Arcand‑Lavigne, M., Lajnef, T., Frenette, S., Carrier, J., &Jerbi, K. (2025). Caffeine induces age‑dependent increases in brain complexity and criticality during sleep. Communications Biology, 8(1), 685.

[2]Zhou J, Qin L. Associations of urinary caffeine metabolites with sex hormones: comparison of three statistical models[J]. Frontiers in Nutrition, 2025, 11:1497483. Writing | Mu Bai

Editor | Mu Bai