Recently, I came across an article in the academic research literature that made me happy: “Sympathetic-parasympathetic system deregulation theory of aging.” Why, you may ask? Because it took all the biological processes that drive aging – the so-called Hallmarks of Aging – and tied them together them in a framework that in essence is what I’ve been advocating for most of my medical career. Namely, that to really understand the body – how it stays healthy, how it gets sick, how it ages – you must try to understand how all the pieces fit together in an integrated whole. 

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In the traditional medical systems I’ve studied, the concept of balance is key. Traditional Chinese philosophy, for instance, talks about the balance of opposing energies, the yin or receptive force, and the yang, the active one. Well, in the article I just mentioned, these sophisticated Western scientists make a persuasive case that the aging process can best be understood in terms of the progressive unbalancing of opposing but complementary forces. 

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There’s the sympathetic nervous system that puts the body in high alert mode – raises body temperature, heart rate, blood pressure, blood sugar, respiration, the works -- and primes us for action. And then the parasympathetic system cools everything down, letting the body reset and repair. Together they make up our “autonomic nervous system” that either controls or at least strongly influences the physiology that operates below the level of conscious awareness. 

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If we’re young and healthy, the sympathetic and parasympathetic systems toggle back and forth almost effortlessly, responding to the day’s challenges and recharging at night. But as we get older, we tend to get stuck in high gear – the sympathetic system dominates – and we pay a price for that. The parts wear out; we generate more metabolic waste. We can’t sleep properly, compounding the damage. Net result: we age faster. 

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What I really like about this new conception is that it puts us – that is, our conscious selves – right at the center of it. No, we can’t say “Heart rate and blood sugar, go down!” and they will. But we can, and we must, develop healthy lifestyle habits and stress-calming practices that will help boost the “chilling out” power of the parasympathetic system, re-balancing the entire autonomic system. I’ve been pushing my “must-do’s” for years, but it’s nice to have a schema that explains their benefits in the context of the big picture, the biggest picture – how well we age! 

Handling the Hallmarks of Aging 

The “hallmarks of aging” explain a lot of complicated biology: mitochondrial dysfunction, DNA mutations, telomere shortening, just to name a few. It’s real. Aging is real. No one is going to mistake a 60-year-old for a 20-year-old. But the easy-to-grasp take-away of looking at aging through the prism of nervous system regulation is: how we help regulate our nervous system plays a big role in determining how soon those Hallmark processes pull us down. If that 60-year-old can find the right balance right between gearing up and gearing down, there’s an excellent chance she’ll be free of the chronic “diseases of aging” that would otherwise lead her towards disability and frailty. 

What’s revving up the over-revving nervous system...

In the morning, the adrenal glands secrete our primary energy hormone, cortisol. It’s what gets us up in the morning. But when cortisol stays elevated after the day’s challenges have been dispatched, it turns into our nemesis, our chief stress hormone that jacks up our entire physiology. 

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Another part of the adrenals secretes epinephrine and norepinephrine (or, to use the lay term, “adrenaline”), the so-called “flight or fight” hormones which we call on for short bursts of energy. They too can spike too high, too often and for too long, essentially burning out the nervous system. If we stay trapped in over-drive, we may simply wind up exhausted, or to use another “F” word, we “freeze.” 

“Inflammaging” – connecting the aging dots.

The primary way an overactive sympathetic nervous system ages us, turbocharging those Hallmarks, is summed up in a word you’ve undoubtedly heard me use before – inflammation, or what some researchers call “inflammaging.”  Let’s connect a few of the dots. The body’s “high alert” state triggers the release of inflammatory molecules or cytokines. This is part of the immune system’s first response to trauma or infection but when these troops are called out too often and don’t return to base, the inflammation becomes a chronic low-grade drain on the body’s resources. That’s why elders can be so susceptible to life-threating infections they would have shaken off a few decades earlier. 

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The high-stress state also interferes with the immune system’s ability to get rid of cells that have grown old or “senescent,” or to strip them for parts to make new cells, a process called autophagy. What happens is, these senescent cells stop doing their assigned jobs and instead devote themselves to spitting out their own cocktail of inflammatory molecules that travel the bloodstream doing damage wherever they feel like it. 

Running out of metaphorical gas.

The body is not an engine (metaphors like “over-revving” notwithstanding) but it does run on fuel, in this case, ATP molecules produced by combusting oxygen, glucose and fatty acids inside the mitochondria, the cells’ power plants, But, aided and abetted by an imbalanced autonomic nervous system, inflammaging contributes to oxidative stress at the molecular level (those free radicals) which are particularly damaging to vulnerable mitochondrial DNA. 

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That can translate to fewer mitochondria to produce energy and more mutations in the DNA which can increase the risk of any number of diseases of aging, including cancer. No surprise, mitochondrial dysfunction is one of the most feared aging Hallmarks. As we age into our elder years, we literally start to run out of gas. Running a cooler engine (sorry, no more car metaphors) is the way to go.  

Unsympathetic waste, running amok.

Generating metabolic energy also generates a lot of waste products, a process that becomes more harmful when the nervous system speeds up the metabolic pace. Oxidative stress also has an inflammatory effect at the organ levels. For instance, LDL cholesterol in the coronary arteries is mostly harmless, until inflammation “arms” them, and they grow into vessel-blocking plaque. Something similar happens in the smaller vessels of the brain. As well, damaged proteins can form the amyloid plaque and tau tangles that are associated with Alzheimer’s disease. 

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High cortisol levels plays its own role in the metabolic damage. It promotes insulin resistance which raises blood sugar levels and left unchecked can lead to type 2 diabetes, what doctors sometimes call “accelerated aging.” Just to add insult to injury, when a stressed-out nervous system makes sleep difficult, we lose out on the “deep sleep” phase when hormones like growth hormone and testosterone are secreted, responsible for cellular repair and muscle growth and maintenance. 

What happens in the vagus nerve doesn’t stay in the vagus nerve.

The nervous system connects a lot of biology. But it’s got its own dedicated system as well, the vagus nerve, the body’s largest, which connects the brain with the internal organs and just about everything in between. When the sympathetic system stands down, it’s the vagus nerve that delivers the parasympathetic’s relaxation message to the immune system, the cardiovascular system, the digestive system and throughout the body. You can easily feel the vagus nerve at work in the gut – not surprising since a core responsibility of the parasympathetic system is to ensure the body has the respite it needs to digest food – “rest and digest” as the saying goes.

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 If the parasympathetic system gets pushed aside by the stressful sympathetic, you may well feel digestive upset, or perhaps “butterflies in the stomach.” The vagus also links gut and brain, the bi-directional gut-brain axis. There’s been interesting new research that links gastrointestinal disorders with “brain fog.” Certainly, the microbiome plays a role here, as we depend on it produce the neurochemicals inside the gut that help govern gut function and very possibly help us to manage our moods at the brain level, courtesy of the vagus nerve. 

Measuring the parasympathetic nervous system.

You may or may not know about HRV but it’s an excellent measure of the parasympathetic response, and it can be easily monitored using an Apple Watch or just about any fitness tracker. When the nervous system is calm – and the nervous systems of fitter people generally calm down faster – heart rate variability goes up. Which means, the more responsive it is to the external environment. 

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Let’s say you need to break into a sprint -- heart rate goes up, the time between beats shrink. Race over, heart rates slows quickly. For the unfit or the stressed-out, or both, the heart rate tends to stay elevated. In which case, bring an HRV tracker to your work-out and monitor both fitness and parasympathetic response. 

Hormesis is your parasympathetic ally.

Paradoxically, one excellent way to improve your parasympathetic “tone” is to stress the body with short challenges that build up resilience and promote deeper relaxation once the challenge has been met, versus the never-ending stress that breaks us down. Exercise – or any kind of vigorous movement like walking briskly up a hill – is a textbook example. Avoiding exercise means smaller, weaker muscles, not what you want for graceful aging. And overdoing hard-care exercise, for instance multiple HIIT (high-intensity interval training) sessions a week, is a great way to exhaust yourself and wash out your immune system. We’re looking for the Goldilocks golden mean here. Relatively brief exposure to very cold temps (ice baths, cryotherapy) or hot (saunas – I’m a big fan of infra-red saunas) can also provide a healthful hormetic shock to the system. Ditto hot and cold showers. Change temperatures during a single shower. 

Breath work is the dream work.

No surprise, mind-body work gives us a direct line into the parasympathetic nervous system. And nothing is stronger medicine than breath work. Slow, regular breathing triggers our “relaxation response.” It’s an important feature of any mindfulness-enhancing practice – sitting meditation, walking meditation, yoga, tai chi, qigong – and I strongly endorse all of it. Here’s one technique that gets to the heart of the calming project – 4-7-8 breathing, derived from traditional yogic breathing. The emphasis is on exhaling for longer than you inhale which is thought to elicit a strong parasympathetic system response. How to do it:

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1. Inhale through the nose for 4 counts

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2. Hold the breath for 7 counts

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3. Exhale slowly through the mouth for 8 counts. 

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Typically, repeat for 4 cycles. 

Find your own “happy space” .

No need to follow anyone else’s rule book here, explore what makes you feel relaxed and centered. But I’ll generalize anyway. Spend regular, unstructured time in nature. Make time for social connection– few things beat a hug when you need one (or even if you think you don’t). And if your sleep habits need a boost here are a few tips on how to upgrade yours.

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