生物与医学2020journals.plos.org
冷水淋浴对健康与工作的影响（2016）
The Effect of Cold Showering on Health and Work (2016)
进阶 · 约 35 分钟读完前置知识：随机对照试验基础、基础统计推断、应激生理学
导读
一项随机对照试验研究持续一个月冷水淋浴对健康和工作的影响，发现冷水组自报病假少于对照组，若同时规律运动降幅更大；但两组自报生病天数相近，免疫机制尚不清楚。
HN 关注点：冷水淋浴是否真有健康收益，讨论焦点是自报病假与真实生病天数的差别、选择偏差以及棕色脂肪等机制证据。
HN 评论精选
这几条评论里：质疑 2 补充 1 亲历 1
亲历11年冷水澡亲历：靠不留温水选项养成习惯，前7年未生病但不认为神奇。
我坚持只洗冷水澡已经11年。它不会变得更容易，但你会迷上洗完后那种很棒的感觉，就像跑步或锻炼：过程难受，但收益远大于暂时的不适。我的诀窍是再也不洗温水澡、绝不妥协，只算最冷的水，早上第一件事。因为一旦体验过温水的舒适，就得反复和它斗争，所以我不信 James Bond shower 之类的做法。直到去年我才在深夜想快点睡觉时洗温水澡（至今约4次）。要养成这个习惯，对我来说关键是别给自己留别的选项。前7年我完全没生病。同时我不认为它对健康是奇迹；如果经常暴露在生病风险中，你照样会病。早期我会在浴室拖延，好办法是给洗澡计时：设5分钟计时器，拿纸记录，尽量5分钟内洗完。不到几周就成了习惯，我享受了大约8年。除了健康、精力和意志力，我怀疑它还有扎实的心理益处。
michalu查看英文原文
I've been taking cold showers exclusively for 11 years now. It doesn't get much easier but you'll get addicted to the great feeling after. It's similar to running or exercise, it sucks to do but you do it anyway because the benefits far outweigh the temporary discomfort. The trick for me was to never use warm shower again and never compromise ... only coldest water available counts. First thing in the morning. It makes everything easier as once you experience that comfort of warmer water you'll have to fight with it again and again. That's why I don't believe in James Bond showers and similar stuff. Only last year I started to take warmer showers if I need to take one late at night and want to get a good sleep fast (I took about 4 so far) ... to build this habit, for me personally, it was paramount to leave no other option. For the first 7 years I haven't been sick at all. At the same time, I don't think it's a miracle practice for your health. You will get sick if you expose yourself to risks of getting sick often enough - it's simple. In the early days, I used to procrastinate in the bathroom ... a good trick was to start timing my showers. I would leave a timer set for 5 min and paper to log time, I tried to get in and out beating 5 min time-frame. In less than couple of weeks it became a habit that I enjoy for some 8 years now. Other than health, energy and willpower, I suspect it has some solid psychological benefits ... you get out in the morning you feel like a superhuman, imagine starting your day in such way and how that compounds over the years. It's great habit to start.
质疑完成试验者可能有毅力选择偏差，需做组内前后比较。
另一种假说：能完成试验的79%的人本身就已经筛选出了“毅力”，或者说他们本来就不会因为小病小痛请假。要检验这一点，不能只把试验组和对照组相比，还需要把试验组自身在冷水淋浴前和淋浴期间进行前后比较。
dardie查看英文原文
Alternative hypothesis: The 79% who were able to complete the trial had already selected for 'grit', or folks who wouldn't skip a day's work for a minor ailment. To check, instead of just comparing the test group to the control group you would need to compare the test group to itself, before and during the cold shower period.
补充补充作者访谈：病假减少但生病天数不少，机制涉及应激反应和棕色脂肪。
这是首个显示冷水澡可能有益健康的高水平证据。连续一个月每次至少30秒冷水澡的人，请病假比对照组少29%；如果还规律锻炼，少54%。参与者自报生病天数平均与正常淋浴者相同，但症状更轻或更有精力，所以更能带病工作。对免疫系统的确切影响不清楚，但知道通路：低温让人发抖，神经内分泌和应激反应使皮质醇升高等，随后转向放松反应；冷还会激活棕色脂肪。棕色脂肪与免疫没有已证实联系，但影响体温调节，燃烧卡路里，可能提高能量代谢、帮助控制血糖，从而降低肥胖和糖尿病风险。
jph查看英文原文
https://hbr.org/2018/03/cold-showers-lead-to-fewer-sick-days The link is an interview with the study author, and excerpts are below. This is the first high-level evidence showing that cold showers can benefit your health. People who took them for at least 30 seconds for one month called in sick 29% less than our control group — and 54% less if they also engaged in regular physical exercise. Participants who took the cold showers actually reported feeling ill just as many days, on average, as the people who showered normally. But either their symptoms were less severe or they felt more energetic, so they were better able to push through the sickness and function anyway. The exact effect on the immune system is unclear, but we do have some knowledge of the pathway through which it works. Cold temperatures make you shiver — an autonomous response to keep your body temperature up. It involves a neuroendocrine effect and triggers our fight-or-flight response, causing hormones like cortisol to increase, shortly before we shift to a relaxation response. Moreover, cold temperatures activate the brown — or good — fat in the body. Brown fat doesn’t have any proven connection to immunity, but it does affect the body’s thermoregulation. When activated, it keeps the body warm by burning calories. It may also increase your energy and metabolism and help control your blood sugar. That could reduce your risk of obesity and diabetes.
质疑质疑结论：自报病假不等于真实生病，存在确认偏误，棕色脂肪证据不匹配。
研究说冷水澡减少了自报病假，但没有减少生病天数，所以不能定论有真实益处。我猜很多 HNer 洗冷水澡，喜欢听它有潜在好处来自我感觉良好，这里确认偏误很多。最高票评论根本没讨论论文，只说冷水澡多棒。研究中一名90秒受试者死亡，很可能不是冷水澡造成，但谁知道；没有实验他/她可能还活着，家属可能会怪冷水澡。David Sinclair 提倡冷水澡，说增加棕色脂肪，但他引用的证据（Lifespan 第110页）里短期冷暴露是4小时、温度可能比冷水澡低得多，所以30/90秒冷水澡能否帮助长棕色脂肪值得怀疑。
wensheng查看英文原文
It says old showering reduced self-reported sick leaves but not illness days. So it's not conclusive it has real benefits. I guess lots of HNers shower cold, they like hearing it having potential benefit so they can feel good about themselves. Lots of confirmation bias here. The top voted comment doesn't discuss TFA, but just how great cold showering is. In the study, a 90-seconds subject died, most likely not because of cold shower, but you never know, without the the experiment, he/she probably would have lived. His/her family members probably blamed cold-shower for it. Dr. David Sinclair advocates cold-showering, said it increase brown fat. But the evidence he cited[1] (Lifespan page 110), the short term cold exposure is 4 hours, the temperature is probably lot colder than cold shower, so it's doubtful a 30/90 second cold shower help growing brown fat. [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5558157/
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