Nick Norwitz breaks down three studies on cold water exposure. One found a 50% metabolic boost but no fat loss over ten days. Another showed dopamine spiked over 250% after one-hour immersions at 14°C. A third identified marisin, a brown-fat hormone that may reduce inflammation independent of weight loss.
Questions this video answers
Better to ask when you should NOT cold plunge: avoid cold plunging 4–6 hours after a workout, especially weight training, because you need the post‑exercise inflammatory response for muscle gains, and avoid plunging right before bed as it can stimulate the nervous system and impair sleep.
Possibly. There is data suggesting a relationship between DHA intake and marisin levels, but the clinical benefit is not definitively proven. Increasing DHA through fish or supplements is generally healthy and may support the pathway.
He has not been regularly cold plunging yet, but he plans to start a self‑experiment assessing daily cold plunges on his lipids, cholesterol, glucose control, and mental health, despite lacking clinical assays for marisin.
Chapters
I've been caught saying I find cold water exposure one of the most unpleasant experiences on the planet. And to be clear, in many respects, I'm not a wimp. I've run 20 miles in silence on a treadmill staring at a wall. I've crutched the 26.2 miles of the Boston Marathon and worked as a professional chew toy for large reptiles at a pet store as a child. They called me the abused animal habituator. But I hate, I hate cold water. I truly abhor it. Still, cold showers and cold plunging are rising as a health trend. And my personal biases aside, I have to ask whether there is solid science to back up this practice. So in this video, I'm going to review 3 papers and explain why I think you shouldn't cold plunge, and also in the end why I think you should. I'll also drop a cool fact about eating fish and cold exposure, and let you know how I may change my personal routine going forward. But let's start with why you shouldn't cold plunge. You shouldn't cold plunge to burn calories or lose body fat. Simply and truthfully stated, it's just not efficient. For example, take a new interventional trial in 15 overweight adults who were exposed to a cold water suit for 10 consecutive days for 1 hour per day. To induce shivering. That's 1 hour of shivering your butt off every single day. To me, that sounds horrible. Now, during the cold exposure, or during cold exposure in general, it's true your body needs to increase energy output, increase thermogenesis, to maintain body temperature. And that did happen in this study. In fact, the cold temperature was individualized per protocol to increase metabolic rate at least 50% above baseline during the cold water exposure. So on that alone, there's going to be a "advantage" of the cold, calorie burning speaking. Sort of. But think about this—you could get more bang for your calorie buck by just walking. Even light walking at 3 mph uses about 3 metabolic equivalents of rest, which is a lot more than the cold exposure in this study. And at the end of the treatment period in this study, a total of 10 hours of cold exposure, so frigid as to cause shivering, fat mass did not change significantly. I will repeat, there was no significant change in fat mass. Kind of demoralizing. That said, I will caveat, this study did report other positive findings, including lower blood glucose and and lower blood triglycerides. Actually, overall, it was a positive results paper, meaning that it did rule, more or less, in favor of the health benefits of cold plunging and cold exposure. However, these benefits were not caused by calorie burning or fat loss per se. So the takeaway from this paper, in my opinion, and as relates to this video, and the balance of other literature as well, is that cold exposure is not efficient for increasing calorie burning and losing fat. Maybe over long durations it could work, but in my opinion, you're better off spending that time lifting weights or just going for a brisk walk. And that's a lot less painful too. But does that mean you shouldn't cold plunge or cold shower? To my own dismay, given my biases and hate of cold water, unfortunately there are other reasons it may be amazing for your health. Darn it. The first major reason you should consider cold plunging relates to a paper you may have heard others talk about, including Dr. Andrew Huberman. It's been doing the rounds. It was a paper published in 2000 by authors whose names I won't even try to pronounce. As a dyslexic, all those accent marks scare the heck out of me. But basically, they immersed subjects in water of different temperatures, 32, 20, and 14 degrees Celsius for 1 hour each in a crossover design. And they found that the cold water exposure at 14 degrees Celsius increased dopamine concentrations by greater than 250%. And importantly, this rise wasn't just a quick spike. This rise was slow and steady, and the dopamine was still elevated well into the recovery period. Now, they only measured up to 1 hour after cold water immersion, but based on the shape of the curve, I'd be surprised if the dopamine rise didn't last for at least several hours after the cold water exposure. I think this is truly impressive and may relate to why some people feel so great after cold plunges. As is commonly reported. Granted, and I'll caveat and clarify, these dopamine levels from the study were measured in the blood, in the plasma, not in the brain, and dopamine doesn't cross the blood-brain barrier. This is a point often overlooked when discussing this study. So to be clear, we don't really know exactly what's going on in the human brain with cold exposure in terms of neurotransmitters, dopamine and other neurotransmitters. However, it is clear that there is a robust activation of the central nervous system with a dramatic change in neurochemicals and commonly reported post-cold high—that giddy, excited, elevated feeling—that is robust and stable for many people. If you've experienced it yourself, you know what I'm talking about. So while there is a lot we still don't know about cold exposure dopamine neurochemicals, I think the mental health boost is one big reason to consider cold plunging or cold showers. Now, for the other reason, and maybe my favorite personal reason, and kind of technical, so bear with me, but reducing inflammation. In particular, I want to talk about a paper that was published in Nature Metabolism where researchers looked at a hormone called marisin. Marisin is a hormone made by brown fat. Brown fat generates heat to protect from the cold. And marisin is made from, wait for it, DHA. DHA omega-3, the same DHA that's in fatty fish like salmon, sardines, or mackerel. Now, what they found in the study was that cold, via activation of the sympathetic fight-or-flight branch of the autonomic nervous system and activation of beta-3 adrenergic receptors, caused brown fat tissue to release more marisin, which decreased inflammation in the liver and the whole body. Now, while most of these experiments were done in animals, in mice, to prove causality, including brown fat transplants, where they transplanted brown fat from cold-exposed animals to other animals to transfer the metabolic benefits, which is pretty cool, right? And did you catch that pun? They also looked in humans to see if activation of this pathway, activation of brown fat, increased mauricin levels. And indeed, it did. So there's probable human relevance here with respect to marisin, brown fat, and anti-inflammatory properties. But in high-level summary of this paper, they find data suggesting that cold exposure, cold plunging for example, increases expression of genes in brown fat that convert the long-chain omega-3 fatty acid DHA into the hormone marisin, which is released from brown fat signaling to the liver and whole body to reduce inflammation, reducing levels of inflammatory cytokines, inflammatory molecules like TNF-alpha, and independent of any weight loss. That's pretty interesting if you ask me, and speaks to how cold exposure may change the hormonal landscape of our bodies by altering how fat tissue and also other tissues like muscle tissue secrete different hormones. I think it's a really exciting and new frontier. Now, rapid question and answer. Question 1: When should you cold plunge? Answer 1: The better question in my opinion is actually when should you not cold plunge? You shouldn't cold plunge in the 4 to 6 hours after a workout, since in the post-workout period, especially after weight training, you actually want an inflammatory response, and cold exposure might actually dampen muscle gains. And you probably shouldn't cold plunge shortly before bed, since it will ramp up your nervous system and may make sleep difficult. Question 2: Can eating fatty fish with DHA omega-3 increase mauricin levels and enhance the anti-inflammatory effects of cold exposure or cold plunging? Answer 2: Possibly. There's data suggesting a relationship between DHA intake and mauricin levels. Now, I don't give this a hard yes because it's not clear what the actual clinical benefit of consuming more DHA would be via increasing mauricin levels. However, if you're a person who doesn't get a lot of long-chain omega-3 in general in your diet, my opinion is it's overall very healthy to do so. So if believing in this mechanism will get you to eat more sardines, salmon, or have some krill oil or something, then I say do it. No harm, potential benefit. Question 3: Do you, meaning me, Nick, cold plunge? Answer 3: I haven't. As I've said, I really am poor at it, but I'm convinced to start. I bit the bullet and got myself a plunge, and I'm going to start with an experiment where I assess the impact of daily cold plunging on my lipids and cholesterol, glucose control, and mental health. Unfortunately, metrics like myricin levels aren't easy to access clinically, and I don't have my own mass spectrometer, otherwise I'd go full on and do exploratory metabolomics. Alas, maybe in future when I have more resources. But it should still be interesting. And while this isn't a sponsored video, I can provide you with a discount code, NICKNORWITZ, if you want to start cold plunging and get a plunge yourself. No pressure from me, but when I mention specific products, I like to have something to offer you, so you can try to do what I'm doing if you're so inclined. And if you have experience with cold exposure, be it cold showers, cold plunging, or just standing out in the snow in Boston in the winter, let me know. I'm really curious about what your experiences are. They inform my research. Anyway, as always, I hope you enjoyed this free metabolic health education. Stay curious, and I'll see you in the next one. Get shivering.
