Want better health, less anxiety, more sleep? You’ve got a nerve

The neurosurgeon Kevin Tracey

MATTHEW V LIBASSI

One of his “holy shit!” discoveries (they don’t say “eureka” in the lab any more) was that the vagus nerve is linked to the immune system and controls inflammation. And that it’s therefore possible to “turn off inflammation”. He says this understanding has been “a game changer”. His experiments led to a new class of anti-inflammatory drug used to treat conditions such as rheumatoid arthritis and inflammatory bowel disease (IBD). The drug is anti-TNF.

The paper Tracey wrote in the journal Nature in 1987 was the first to indicate that anti-TNF mAbs (monoclonal antibodies) have anti-inflammatory effects. Several years later, Marc Feldmann and Ravinder Maini successfully used anti-TNF in a clinical trial to treat patients with rheumatoid arthritis. Now, brand names of these biologics include Humira and Remicade, which are widely used in the UK and elsewhere.

So how does this “great nerve” have such capacity to transform our health? It extends from the brainstem, through the neck, chest and abdomen, and connects to organs including the heart, lungs and digestive tract. As Tracey notes: “You have two vagus nerves, one on each side of your neck. Each one contains 100,000 fibres.”

Through these fibres, “the vagus nerve carries signals back and forth from the brain to the body” and “each of those fibres has a specific job”. Largely through mice studies, scientists have been able to examine them “one at a time, and work out: this one seems to go to the stomach and seems to control acid secretion, this fibre goes to the liver and seems to control glucose balance, and this one — my colleagues and I discovered — goes to the spleen and can turn off inflammation.”

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Eighty per cent of the signals go from the body into the brain. You eat lunch or step into a hot bath and “these changes in the body are instantly transmitted through the vagus nerve to the brain, almost like an electrical reporting mechanism, like a text message. Boom! The temperature went up! Boom! The stomach is full!” (Imagine that one day soon, instead of GLP-1 drugs, a computer chip to the relevant vagus nerve fibres could tweak your hunger signals.)

As Tracey explains in his new book, The Great Nerve — The New Science of the Vagus Nerve and How to Harness Its Healing Reflexes: “The brain listens to the body through the vagus nerve and then talks back.” He says: “These incoming signals activate the brain and vagus nerve to send signals back to the body to maintain balance.” This is its critical role.

As data-driven fitness fans will know, you can gauge your vagal tone — the activity of your vagus nerve — by measuring your heart rate variability (HRV) on your wearable. “What you’re looking at with HRV is the average time between heartbeats,” Tracey says. “Every time the vagal nerve fires, it prolongs the time to the next heartbeat.”

It’s variable because the strength of the vagal nerve signal fluctuates, and because opposing forces (the sympathetic nerves, part of the fight-or-flight system) speed up the heart, he says. Part of the fight-or-flight system is norepinephrine, which hurries you up, and the vagus nerve — chief operating officer of the rest-and-digest system — releases acetylcholine, to slow you down.

Broadly, when your vagus nerve is healthy, so are you. If not (for example, if you’re chronically stressed, and less able to rest and digest), consequences can range from poor sleep to low mood and illness.

But as Tracey says, when you stimulate the vagus nerve, you can modify the signals travelling down into the body — or up into the brain. A quarter of a million people with drug-resistant epilepsy have vagus nerve stimulators implanted in their neck. “And the signals going up into the brain seem to suppress the amount of seizure activity in the brain,” Tracey says.

His research has shown that vagus nerve stimulation — either with an electrical implant or focused ultrasound, not a vibrating bracelet — has the potential to reverse inflammation-linked diseases including rheumatoid arthritis, IBD, multiple sclerosis, diabetes, obesity, depression, Alzheimer’s and Parkinson’s.

Is it worth paying for a vagus nerve stimulating (VNS) device that you clamp to your ears and that claims to alleviate stress, anxiety and burnout? Some devices are approved by the US Food and Drug Administration and the European Medicines Agency for specific ailments, such as headache, but it’s best to read the small print, Tracey says. Some VNS devices are authorised for use in the UK for specific conditions. These include LivaNova for drug-resistant epilepsy treatment and gammaCore for episodic cluster headache and pain associated with migraine.

Small studies have shown that “stimulation with a Tens [transcutaneous electrical nerve stimulation] unit, which puts a very gentle electrical current into the cartilage of the ear, can reduce inflammatory markers in the bloodstream”, for example. But while there is a branch of the vagus nerve to the ear, there are other nerves too, he says — so who knows what you’re stimulating.

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However, unless the vagus nerve has been damaged (by Covid, for example, with research suggesting that “the Sars-CoV-2 virus infects the vagus nerve, which damages the fibres directly” and causes inflammation in the nerve itself, according to Tracey), we can increase vagus nerve activity through lifestyle habits. How do we know if we’re increasing it? Broadly, if we succeed in slowing our resting heart rate.

By doing so, we’ll lower our risk of diseases, and possibly even lengthen our life. “Human populations with slower heartbeats tend to live longer than human populations with faster heartbeats,” Tracey says.

It all comes back to inflammation. And Tracey’s decades of pioneering research point to the same thing. “The vagus nerve has a very important role in turning off inflammation. Just like brakes in your car have a very important role in stopping your car.

“Primarily because I believe my own data,” he says. “I looked critically at things in my life which would increase the vagal tone or the vagal nerve activity in my own body.”

Here is what he does.

He meditates daily

“Everybody agrees meditation is good for you,” Tracey says. “I try to do it every day — sometimes twice a day.” When the meditating brain is observed on a functional magnetic resonance imaging scanner, “you see very interesting parts of the brain light up associated with relaxation or concentration. There’s evidence for enhanced learning and memory even.” He can’t explain as a neurosurgeon how it works, he notes. But he believes it contributes to lessening anxiety, shown to reduce inflammation. To meditate, Tracey sits comfortably, focuses on his breath, or an intention. “[Then] I simply note the emotions, thoughts and sensations that arise.” He’s aware but not reactive, allowing them to pass.

I tell Tracey that my husband and his identical twin had similar HRVs, shared on their Whoop wearables. His twin left corporate life and trained as a meditation teacher. His HRV is now nearly three times as high as my husband’s. “As a scientist I find those things fascinating,” Tracey says, noncommittally. Some studies find meditation enhances vagal tone, but a review of 19 randomised clinical trials indicated that it didn’t, he reports. But, regarding meditation’s potential to reduce inflammation “the evidence is more promising”, he says, and that in turn is good for blood vessels, organs, heart and brain.

He does a range of regular exercise

“I do some treadmill or elliptical training for cardiovascular toning, I do some stretch bands or weights for strength training, and I do some yoga or balance for proprioception training,” Tracey says. He adds: “As a general guiding principle, the things that keep you healthy tend to increase your vagal tone and decrease your inflammation and lengthen health span. The things that tend to give you a higher HRV and a lower resting heart rate are the things that your grandmother and your physician tell you to do. Eat a balanced diet, get enough sleep, try not to have too much stress in your life, exercise regularly.

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He practises cyclic sighing most days

A happy alternative to hyperventilation is slow deep breathing. It stimulates the vagus nerve and can also reduce inflammation, Tracey says. Research from Harvard Medical School and Beijing Normal University has shown that “deep, diaphragmatic inhalations followed by prolonged, slow exhalations decrease your heart rate and increase your vagal tone”. And Stanford researchers studied breathwork exercises, including cyclic sighing (long exhalations) and box breathing (inhale, hold breath, exhale for equal duration). Cyclic sighing showed the most significant effects on alleviating stress. “Most days I do several minutes of cyclical breathing,” Tracey says. He takes one big inhale, a short further inhale — “like a big sniff” totalling three seconds — then a long slow exhale totalling seven seconds.

He turns the shower to cold

“One way of stimulating the vagus nerve is through cold exposure,” Tracey says. “You can do it by putting your face in a bowl of cold water. The cold activates the trigeminal nerves, which send signals into your brain, and the brain — through the vagus nerve reflexes — sends signals to slow the heart.” But that’s very different from taking an ice bath or turning the shower to freezing cold (“just try it”), where the immersive exposure to the cold creates a massive stress response. “It feels like all the air’s been sucked out of your body. And then when you do get your breath back, there’s a massive fight-or-flight response”. He adds: “As it turns out, a massive fight-or-flight response turns off inflammation.”

Even more interesting, he says, is that “if you stay in the cold until you adapt to the cold” — you can tell by feeling your pulse — “your body starts to relax, and in that relaxation state, your heartbeat slows. Now you’re stimulating your vagus nerve.” Tracey has been turning his shower to cold several times a week for years. “Every time that water hits you, it feels like the worst thing in the world,” he says, but “I don’t mind it any more”. Tracey stresses that there’s no long-term health guarantee. “But it’s a Pascal’s Wager for me. I don’t mind doing it, and if it helps me, great, and if it doesn’t?” He grins. “I may never know.”

The Great Nerve — The New Science of the Vagus Nerve and How to Harness Its Healing Reflexes by Kevin Tracey is out on Thursday (Penguin Life, £22)