It’s the end of November and I’m standing under a freezing cold, outdoor shower in too-short shorts and a sports bra.
I’ve spent 20 minutes sweating it out in a ‘wild sauna’ in a tiny tree-lined space carved out of an industrial estate in Bristol, UK.
And now I’m about to lower myself into frigid water in a tin bath. What am I thinking?
What I’m hoping is that immersing myself in cold water should achieve one of the wellness trends of the moment and stimulate my vagus nerve.
This long, winding and highly branched nerve, which connects our brains to many of our organs and muscles, is part of the ‘rest and digest’ (parasympathetic) part of our nervous systems. It controls vital functions like heart rate, breathing and digestion.
Enthusiasts claim that activating this nerve can help with everything from digestive disorders to long COVID and insomnia.
Across the social media scene, a bevy of high-tech devices, wellness protocols and nervous system ‘resets’ offer us the chance to 'hack' our nervous systems, and get our vagus nerves going. Dousing yourself in cold water is one of those methods.
Personally, I’m sceptical about the hacks and resets. But as psychologist Dr Sylvain Laborde from the German Sport University Cologne in Cologne, Germany, tells me, the vagus nerve does indeed get involved when the body enters cold water.
Initially, it’s actually the sympathetic branch of our nervous system that’s triggered by the shock. This is the ‘fight-or-flight’ response to stress that causes our heart rate to increase as energy is diverted away from digestion and our eyes dilate.
The vagus nerve then comes in to counterbalance this. It acts as a brake, telling our body to relax again and helping us to stabilise our heart rate so we can carry on with normal functions.
Laborde’s own interests lie in training this self-regulatory response so that athletes can improve their abilities to withstand and recover from hard workouts, focusing on simple methods of stimulation such as breathing techniques.
Other researchers, meanwhile, are targeting the vagus nerve with hi-tech nerve stimulators, aiming to treat common conditions like depression, stroke and much more.
What I want to know is: are they overcomplicating things? And is sitting in a cold tub actually going to do me any good?
Deep rooted research
Vagus nerve stimulation (VNS), as a concept, is nothing new. It goes back to the 19th century and early epilepsy treatments.
The American neurologist James Leonard Corning tried to solve the problem with neck braces and fork-like implements that compressed the carotid arteries (the two major blood vessels in the neck) and electrically stimulated the vagus nerve on its way to the head – devices he said reduced epileptic seizures. These early devices looked a little archaic and could cause dizziness and fainting.
But they weren’t that far-removed from some of those on the market today, says Dr Christopher Austelle, a psychiatrist at Stanford University, California, who studies VNS.
“There are modern-day VNS devices that you can hold over your neck,” he says, noting that the GammaCore device, for example, works “very similarly” to the old-fashioned ones.
The GammaCore – a sleek, white, handheld machine that looks not unlike an electric shaver – was approved for treating headaches in 2017 in the US.
Other devices more reminiscent of wired headphones are designed to stimulate fibres of the vagus nerve that branch into the outer ear. Austelle describes this feeling as a mere ‘tingling’.
But these external devices are by no means the first modern vagus nerve stimulators.
A century after Corning, researchers returned to the epilepsy problem, testing surgically implanted nerve stimulators that plug into the branches of the vagus nerve found in the chest.
The implants were approved in the US in 1997, and today hundreds of thousands of people are fitted with them. They don’t work for everyone, but for some people, they can eliminate half their seizures. They’ve also shown promise in treating depression, although larger trials are still ongoing.
Because of the cost, however, not to mention the need for an operation, testing has been limited. And the implants do come with some unwelcome side effects, including voice changes.
However, modern external devices now offer researchers the opportunity to test VNS safely and cheaply for a whole range of new conditions.
“There’s not nearly as much risk with putting electrodes on the ear as compared to a surgery,” Austelle says. “But it also opens a lot of doors for us to understand more about how VNS works.”
Which is huge, because this still isn’t clear. Even in the conditions it’s approved to treat, scientists can't say for certain why stimulating the vagus nerve helps.
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There are theories that it could help improve blood flow or change chemistry in the brain, or cause certain areas of the brain to be stimulated, but no one’s sure. That means the only way to know how to get the best results is to test it.
A trial Austelle is involved in, for example, is currently recruiting over 140 patients with epilepsy and depression to study the effects of their vagus nerve stimulators.
“We know the vagus nerve travels all over the body, and regulates organ function both in the chest and abdomen. So the study will shed a lot of light on the effects of different parameters on those organ systems,” he says. Though he doesn’t expect any results until at least the summer.
Meanwhile, Austelle has been exploring how external devices modify the type of shock response I get by climbing into a cold bath.
In a 2025 study by his team, people put their hands or feet in an ice bath while wearing an earpiece. Those who got VNS through the earpiece saw a smaller rise in heart rate compared to those who only thought they were getting it, suggesting that stimulating the vagus nerve in this way enhances its ability to regulate, or, in Laborde’s terms, act like a brake to our stress system’s accelerator.
Breathe yourself better
Given its commanding role in the nervous system, and the fact that the vagus nerve infiltrates so much of the body, it’s no wonder researchers are testing VNS for an ever-growing list of conditions.
A quick search of academic papers spits out studies on everything from Crohn’s disease and long COVID to irritable bowel syndrome and insomnia.
As someone who often struggles to get enough sleep, I’m certainly interested in the results. But given all this research is still ongoing, I’m not keen to splurge on an expensive earpiece.
Luckily, Laborde has other ideas – and they don’t involve getting into a cold bath or pool.
“I would put the cold swim to the bottom of the list,” he says. “Why? Because it should not be done without supervision. If you have no experience with it and do it alone, we can imagine the consequences.”
I do have a plunge pool pal, but I take his point. What Laborde recommends instead is also cheaper.
According to Laborde, scientific studies show that one of the best things you can do for your vagus nerve response is, wait for it: slow breathing.
“Boring”, he admits, but way more accessible than a nerve stimulator that could cost £600 (approx. $800). And Laborde is so convinced it works, he’s been breathing slowly for 15 minutes a day for over a decade.
He’s been doing the science, too. A recent review he led combed through 223 studies on slow breathing techniques, which generally aim to reduce breaths from between 12–20 per minute to about six.
This seems like a big drop, but when I try it out, I don’t find it that difficult, at least for a couple of minutes.
Overall, Laborde’s review suggests that slow-paced breathing has a positive effect on the parasympathetic regulatory response influenced by the vagus nerve, not only during a breathing exercise, but also after it – and, crucially, with regular practice.
Other studies using brain imaging hint that, over time, this practice could even restructure the brain, including parts involved in processing emotions.
But how do scientists, and the rest of us, keep track of how the vagus nerve is operating? It’s hard to get a full picture of a nerve whose threads are interwoven in tissues across the whole body.
Most of the studies in Laborde’s review only take a snapshot by looking at other vital signs. They focus on the heart, using a metric called heart rate variability (HRV) – something you might be familiar with if, like me, you own a fitness tracker.
HRV gauges the change in spacing between heartbeats, measuring the control the vagus nerve exerts on the heart. You can get measurements from a standard heart rate monitor on a wristwatch.
As far as figures go, the higher the better – higher means more variability. A regular heartbeat might sound like a good thing, but it’s considered better if the intervals fluctuate throughout the day, because it suggests an ability to adapt to stress.
Different strokes
But heart rate variability may not always be the right read-out – hanging everything on heart rate could be too narrow-minded for a nerve that’s such a jack-of-all-trades. And there are some conditions that do seem to benefit from VNS despite having no impact on HRV.
So could the expensive earpiece be worth the investment for some of us, at least?
I talk to Dr Ali Ali, a neurorehabilitation expert at the University of Sheffield who is also an NHS consultant and stroke specialist. He’s currently testing ear-stimulating VNS devices for some of the stroke patients he sees who have been left with arm weakness.
“Arm weakness is one of the big priorities that clinicians feel we need to develop treatments for,” he explains.
“It’s a big barrier for people getting back to work, leisure activities and family activities, and the only real treatment we have that’s accessible to a lot of people is physiotherapy.”
Now, however, early studies suggest that when physiotherapy is combined with VNS, it may have better results.
Based on a 2018 pilot study in 12 people showing positive effects, Ali’s team is currently recruiting around 270 patients for a larger study across 19 different UK centres.
Patients for this ‘TRICEPS’ (Transcutaneous Limb Recovery Post-Stroke) trial will be asked to use a VNS earpiece for one hour a day, five times a week, for 12 weeks, alongside arm exercises.
According to Austelle, stroke is one of the conditions showing “really promising results” with VNS, although until studies like Ali’s are completed, more of the evidence comes from implanted devices.
What we can’t assume is that every stroke survivor will benefit from an earpiece. But that’s hard to tell someone struggling to get back to work, especially when the technology is already available to buy.
“We’ve had maybe 10 or 15 individuals for the TRICEPS study that have finished their treatment and then emailed to say, ‘I want to buy one directly from the company’,” says Ali.
“And we have had to reply really sensitively to say, ‘We’re really pleased you had a good experience, but we still don’t know whether the treatment works.’”
Ali is also concerned about device makers promoting their devices as cures for conditions they haven’t been tested for, or claiming that evidence from trials of similar devices applies to their own. You have to be “a bit sceptical,” he says, particularly of those devices that don’t have the European CE marking signifying it has been assessed for health and safety.
Across most conditions, it seems, research is lagging behind the claims of device makers.
“We still need the bigger, more rigorous trials to definitively show the efficacy, especially of the [external] devices,” says Austelle, who notes that there have also been no head-to-head trials of the external devices versus the implants. But it “seems like” they target the same areas of the brain, he says.
Doubts aside, it’s unsurprising if those suffering from more serious health issues are willing to try it.
Meanwhile, I just want a better night’s sleep and to recover quicker from a hard run. As I ease myself into the freezing cold tub, I visualise the blood retreating from my extremities in shock, assured that the vagus nerve will kick into gear to calm things down.
Whether my cold plunge will have any long-lasting effect remains to be seen.
A 2025 study hints that immersing yourself in cold water can have wide-ranging health benefits, including for the immune system. However, HRV data suggests vagus nerve effects may last no longer than the dip itself.
For people like me, some daily breathing exercises might be enough to keep my vagus nerve in check.
In fact, from the research I’ve been doing, I wonder if I’ve been overthinking it. Wouldn’t anything that relaxes me help? What about yoga? Or going for a nature walk? Or singing?
Laborde is quick to point out that at least some of the benefit from these activities stems from regulating our breathing.
But he does concede that it’s the most obvious things we need to focus on first for optimal functioning: sleep, nutrition and exercise.
“These are the basic ones for every human being,” he says. “First of all, get those three right and then we can talk about stimulating your vagus nerve.”
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