How the Vagus Nerve Affects the Immune System

Does stress ever feel like a real, physical threat to you? Nothing has actually happened, no danger is in the room, yet your body acts like something is about to attack you.

As strange as it may seem, to your nervous system, that reaction makes sense because, to your nervous system, the threat is real.

Your brain scans for danger all the time. A small almond-shaped part of the brain called the amygdala flags anything that might be a threat. It then signals another region, the hypothalamus, to get the body ready to respond. The hypothalamus turns on two stress systems at once. The first is the sympathetic nervous system, which releases adrenaline. The second is the HPA axis, which releases cortisol.

This is the fight-or-flight response. Your heart speeds up, blood pressure rises, muscles tense up, digestion slows, and focus sharpens.

The body runs this same response whether the trigger is a wild animal, an injury, or a short message from your boss.

Research suggests physical and psychological threats activate the same two stress pathways — the sympathetic nervous system and the HPA axis — releasing the same core hormones, even though the brain processes each kind of threat a little differently.

Physical threats are handled quickly by lower brain regions. Psychological threats involve higher-thinking areas — the prefrontal cortex, amygdala, and hippocampus. That's because they need to be interpreted. A deadline is only taken to be dangerous once you’ve decided it is. Your body then reacts to it as if it had teeth.

Why modern life confuses your stress system

Fight-or-flight evolved for one kind of problem: short, physical, and over quite quickly. A predator shows up, you run, fight, or freeze, and within minutes the threat ends. If you survive, your body powers down and gets back to normal.

The scientist Robert Sapolsky explains this in his book Why Zebras Don't Get Ulcers. A zebra escapes a lion and returns to grazing within minutes. It does not sit under a tree worrying about the next attack.

Humans do. We ruminate. Cows are called ruminants because they chew cud. We chew the cud of our minds — endlessly replaying past mistakes or worrying about the future.

We can create a threat just by thinking about one. A deadline three weeks away, a text someone hasn't replied to, a meeting tomorrow, a vague message that could mean two things. Your nervous system treats each of these like real danger, but unlike a predator, they do not go away … they stretch out for hours, days, weeks.

Scientists call this an evolutionary mismatch. Your ancient threat system has not caught up to the modern world it is running in.

Why notifications, meetings, and deadlines feel so heavy

Modern stress has three features that make it especially hard on the nervous system.

It is anticipated.

Your body reacts to threats that have not happened yet. The dread before a meeting can feel as physical as the meeting itself.

It is social.

Conflict at work, feeling left out, or unclear messages can activate the same circuits as physical danger. Research suggests social pain and physical pain use some of the same brain pathways.

It is always-on.

Notifications, group chats, open inboxes, and constant availability mean your nervous system rarely gets the all-clear signal. The threat never fully ends.

A predator encounter ends, an inbox doesn’t.

What this does to your body over time

When the sympathetic nervous system and HPA axis stay active for too long, the body builds up what researchers call allostatic load — the wear and tear from being on alert too often.

Long-term cortisol dysfunction affects heart health, immune function, sleep, memory, and metabolism. Sapolsky’s research shows that chronic stress also weakens the parasympathetic nervous system, the part that calms the body down. Over time, the body has a harder time switching off even after the stress is gone.

How to read your stress response differently

Understanding the biology gives you new options.

If a tight chest before opening an email is a flaw, the only fix is to try harder, care less, or push through. None of those work, because none of them deal with the system causing the reaction.

But if a tight chest is your amygdala doing its job in the wrong environment, the question changes. How do you help your system finish the response and return to a calm state?

This is what nervous system regulation means. There’s no need to suppress your stress response when you can support your rest and recovery response.

Slow exhales activate your vagus nerve, which calms your body. Short pauses between stressful moments let your system register safety more often. Sleep, movement, and steady recovery habits train your nervous system to settle down more easily over time.

Evidence indicates regulation is trainable. Vagal tone — a measure of how well your parasympathetic nervous system works, often tracked through heart rate variability (HRV) — improves with steady, repeated practice. The goal is to handle stress by giving your body the signal that the threat has passed.

Vagus nerve stimulation is a precision-engineered and convenient way to do that every day.

The takeaway

When your body reacts to an email like it is a predator, don’t think of it as overreacting. It is a survival response, largely out of your hands. Your nervous system is doing exactly what it evolved to do: spot a threat, ready reserves for action, protect you.

The mismatch is in the environment, not in you.

What do you think of when you think of yoga? Really supple people bending themselves into impossible shapes? Incense-filled rooms with rows of people lying down with their eyes closed? A gong? Is yoga slow and stretchy to you, or hot and hard? Plain and simple, or a complex mix of movement and Sanskrit?

The point is, yoga isn’t really one thing. It consists of multiple styles. Each instructor brings their own flair, wisdom, and understanding to each class. And it takes place in every imaginable setting.

Whatever you think yoga is, there will be an example out there to prove you right. But if you say “yoga is not for me”, you are almost certainly wrong.

While yoga is an ancient practice, it has many practical applications and benefits for the modern world. There are three ways yoga can support your daily life.

Yoga is a good exercise

Yoga’s physical exercises are called asanas. Asanas help develop strength, muscular and cardiovascular endurance, stability, and flexibility. Regular practise develops power, speed, agility, coordination, and balance. As a result, yoga can improve your heart and musculoskeletal health, protect against injury, and improve sports performance.

Like all forms of exercise, yoga boosts endorphins (feel-good hormones) and reduces cortisol and adrenaline (stress hormones). It also improves brain function by promoting the growth of new brain cells (neurogenesis), increasing blood flow, and boosting connections between neural networks in your nervous system (neural connectivity).

Yoga promotes healthy breathing

In yoga, movement is linked with breath (pranayama), and deep breathing is encouraged. Deeper breathing brings more oxygen to your muscles, enabling them to work more effectively. It also fuels your brain, helping to maintain focus. Controlled deep breathing also activates the rest-and-digest part of your nervous system (parasympathetic nervous system), shifting your body into calm mode and promoting better nervous system regulation.

The breathing you practice during yoga sessions can move into your everyday life. Deeper, more efficient breathing becomes second nature, and, when feeling overwhelmed, you are more likely to turn to breathing to restore calm and regain a sense of control.

Yoga is relaxing

While many types of yoga are far from relaxing, savasana (relaxation) is a core principle in yoga because the ability to rest and recover is essential to living a balanced life.

Rest is necessary for our brains and bodies to repair and rebuild. Resting refills our batteries and calms our minds, enabling us to refocus on what’s important and giving us the energy to achieve our goals.

In today’s fast-paced world of constant stimulation and pressure to achieve, many of us need to learn how to relax. Regardless of style or purpose, most yoga classes will end with a period of savasana, whether it’s just a couple of minutes of quiet time or a longer period of guided meditation.

This often feels strange or difficult to begin with, especially if you have ADHD, are a fidgeter, or tend towards constant busyness. But like all skills, we improve with practice. And savasana is not about clearing or ignoring our thoughts; its purpose is physical rest, nervous system rejuvenation, and the observation of thoughts without dwelling on them.

Yoga can be a space for simply being present, without the pressure to ‘do’.

Finding the right style

First, look for a class, in person or online, that fits your goals and personality.

If you like challenges and want to make big fitness gains, try Vinyasa, Flow, Ashtanga, or Power yoga. These classes will include exercises such as push-ups, arm balances, and explosive movement to build strength and power, and allow only minimal rest to increase your heart rate and build stamina. These classes can be as physically challenging as CrossFit or HIIT.

If you want to learn the fundamentals of yoga and get an all-round workout, plus some relaxation, look for Hatha yoga. Hatha classes are accessible to all levels and usually include strength, balance, and flexibility.

If you are a bit of a perfectionist or like to delve deep into the technical aspects of things, try Iyengar classes, where the focus is on alignment, with lots of detailed cueing and props to help you achieve the best version of each position. Iyengar can also be helpful if you have an injury or chronic condition, as it’s unlikely you will push too hard and make it worse.

If you love to sweat, Hot or Bikram yoga is done in a heated room. This style warms the muscles and connective tissues for deeper stretches. It also increases your heart rate, bringing great cardiovascular benefits.

If you’re looking to focus on activating your parasympathetic nervous system, seek out restorative classes. Restorative yoga encourages passivity and stillness, relying on soft props (bolsters and blankets) to reduce the physical exertion needed to achieve poses.

Finally, Yin yoga is a slow-paced class where poses are held for several minutes. This targets deep connective tissues, improving flexibility and circulation. The challenge of Yin yoga is both physical and mental: holding yourself at the edge of discomfort while avoiding fidgeting or distraction.

Giving it a go

Yoga is for you. You only have to spend some time finding the style, teacher, and community that appeal to you.

Do you want a relaxed atmosphere where students and teachers interact during class, or do you prefer a silent practice to allow you to focus only on yourself? Are you open to the spiritual side of yoga, or is it all about the science of the exercises?

Before joining a class, check out the instructor or studio’s website and social media, and don’t be afraid to contact them for clarity on what’s on offer. Online classes and apps are a great way to explore different styles, and they give you the flexibility of practicing when and for how long you want.

yōjō offers simple movement activities on our app. They only take a few minutes, are mostly drawn from yoga, and can be the perfect way to start experiencing its benefits.

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A few days ago, we passed the 12,500 VNS sessions mark. That’s 12,500 pre-session face scans, 12,500 VNS sessions, and 12,500 post-session face scans. That is a lot of data. And here’s what it’s telling us so far.

30 minutes of yōjō = 90 minutes of meditation

A single yōjō vagus nerve stimulation (VNS) session lifts heart rate variability (HRV) by 3.76 ms on average. In a study published in 2025, 90 minutes of meditation lifted participants’ heart rate variability by 4.68 ms.

Both practices produce real physiological change. They share the same target: parasympathetic activation and increased vagal tone. We’re comparing them with sustainability in mind. For most working professionals, 30 minutes of hands-free VNS might be easier to manage than 90 minutes of meditation.

HRV improvement compounds

On average, yōjōers see a 1.5% improvement in HRV from established baselines after 1 month. That doesn’t sound like much, but the rate of change increases over time.

Month 1 — HRV up 1.5% from baselineMonth 3 — HRV up 4.7% from the baseline set in Month 2Month 6 — HRV up 16.5% from the baseline set in Month 5

Nervous systems respond better the more you train them.

yōjōers have a favorite mode

Of all these thousands of sessions, 49% were done in the Stress Mode. Sleep Mode came in second with 27%.

We’ve also seen a healthy spirit of exploration. Most of our members try all modes before eventually settling on one.

Why this matters

This shows that daily vagus nerve stimulation effectively supports nervous system health. It also proves that technology that was only a few years ago confined to the clinical setting can, in fact, fit into real life.

And it proves that yōjō’s device + human coaching + gentle data tracking boosts adherence, helping people stimulate their vagus nerve every day (more than once a day on average, based on the data).

Everything we’re learning — how our members yōjō, why they yōjō, what yōjōers need from their device, coach, or platform — is going into yōjō experience and making a bigger positive impact.

Much of it has already helped refine the yōjō Stone, our latest device, launching towards the end of the year.

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