William James, a philosopher and one of the first educators in psychology said that the ANS “forms a sort of sounding-board, which every change of our consciousness, however slight, may make reverberate” (James 1884, p. 191; Ellis & Thayer 2010).

Short Version

Our bodies are responsible for so many different activities at any given moment, and we do not have the physical ability (nor the attention span 😄) to regulate all of them. The jobs which we (for the most part) cannot consciously undertake are controlled by the autonomic nervous system (the ANS). The ANS is made up of the parasympathetic (PNS-rest and digest) and sympathetic nervous systems (SNS-fight or flight). When the SNS is activated it slows down or stops some of our bodies’ vital functions to focus on what is urgently needed in that moment. Whereas the PNS allows for relaxation and the storage of energy.

When people live with excessive SNS activation it can lead to a host of major health problems, but luckily there are very easy ways to ensure you have a healthy autonomic balance.

Exercise, diet, sleep, breathing, meditation, and cold exposure to name a few!

See the long version for a more in depth exploration of these concepts…

Long Version

Even if we are not aware of it, every moment of every day, our body is working to ensure that we stay living. We breathe, digest food, combat illness, and our hearts work to pump blood throughout our bodies. Those important functions would not be possible without the control of the autonomic nervous system (ANS) (Auto meaning self and nomic meaning governance), our bodies’ self governing nervous system. The ANS has two subdivisions; the sympathetic and parasympathetic nervous systems (SNS and PNS respectively). When predominant, each system has a unique impact on our bodies, but our lifestyle choices can impact which is more active and when.

The SNS, is most commonly known as the ‘fight or flight’ function, and it is activated in times of intense stress. Examples would include, if we were being chased by a wild animal, in a fight with another person, or potentially even stressed about school or work. Other factors such as diet and exercise play a part, but we will discuss that later.

So what do higher levels of SNS activity mean for the human body?

In order to help performance under high stress situations, the body increases lung capacity and sends high concentrations of oxygenated blood to the places where it is needed most (Alshak 2019). Obviously, this function is essential for us to survive but our bodies are not meant to exist in such a state for prolonged amounts of time. Because the body is hyper focused on the most essential functions for survival (i.e. heart rate, breath, oxygen distribution) it stops other less important but nonetheless vital functions. With increased activation of the SNS there can be lessened ability to digest, worse sexual function, and if excessively activated due to chronic stressors it can in the long run lead to hypertension, heart failure and potentially lead to or worsen obesity (Alshak 2019; Hamilton & Meston 2013; Harvard Medical School 2020; Lee 2009). And in fact, the reverse is thought to be true as well, that obesity is a cause of further SNS activation due to the extra stress the body has to handle (DiBona 2013; Hall 2010). At this point you may be thinking that our SNS does more harm than good for our bodies, but it is important to emphasize, that is not necessarily the case! The negative long term effects come when we have prolonged and excessive sympathetic activation. As mentioned earlier, the SNS is essential to our survival and wellbeing. Besides being an innate life saving tool, it allows us to have fast reaction times, it can cool our body down by managing our sweat, increase performance in sport, and more (Alshak 2019; Matsumura 2021). It has even been claimed that the SNS can be consciously activated and utilized to voluntarily combat sickness (Wim Hof Method).

The parasympathetic nervous system, also referred to as the rest and digest mechanism, is in control while the body and mind are at rest (Russo 2017). While it is predominant, it helps digestion, blood flow (via vasodilation), increases sexual function, decreases inflammation, senses attacks on the body, and allows for the storage of energy (Tindle 2021; Waxenbaum 2019; Hamilton & Meston 2013; Liu 2017). In addition to being useful on a day to day basis the energy storage that happens due to the PNS serves as a restorative mechanism before or after SNS predomination. In other words, the PNS is helpful to proactively counterbalance the energy expenditure that arises because of the SNS (Liu 2017).

So how can we decrease sympathetic and increase parasympathetic activation on a day to day basis so our bodies’ vital functions continue and we optimize our healthy lifestyles?

This is certainly a field that requires more research but there are some techniques that are thought to lead to the ability to actually regulate our ANS. The logic behind some of the techniques are supported by the idea that low levels of oxygen in the human body cause increased sympathetic activation, so increasing, or maintaining high oxygen levels helps to achieve the desired goal (Hansen 2003).

The below recommendations are not replacements for advice by medical professionals…

Exercise

Exercise is a prime example. When we engage in physical activity our lungs take in oxygen at a faster rate because our body needs to replace what it is losing. But exercise does not cause permanent oxygen depletion (hypoxia), our bodies recover from the work done and our lung capacity increases. Furthermore, with frequent exercise, the body requires less and less oxygen for any given activity (Breathe 2016).

Also, passive stretching routines have also been shown to increase parasympathetic activity, both during and after the practice (Inami et al. 2014; Healthline 2020).

Diet

Diet is another important lifestyle factor that influences ANS activity. Eating foods that cause inflammation in the body (such as: refined carbs, fried foods, soda, red meat, margarine, lard (Harvard Medical School 2021)) can then increase sympathetic activity because inflammatory conditions are commonly associated with hypoxia (Bartels 2013; Minihane 2015). On the other hand if you take care to include foods that promote a highly oxygenated environment in your body, sympathetic activity can see a decline. There are a number of examples of nutrients to help decrease sympathetic activity…

Hemoglobin, an oxygen carrying protein, is responsible for moving oxygen from our lungs into our bloodstream (UCSF Health). And healthy levels of this protein can be achieved with the right amount of iron intake (Abbaspour 2014). Foods with a high iron content can include… (Health Direct 2021)

• Red meat (makes an appearance here and on the inflammation list, so make sure to get iron from a variety of sources)

• Liver

• Eggs

• Nuts

• Legumes

• Leafy green veggies

• Oats

• Tofu

(As with most things, consume in moderation. High iron levels can be responsible for the creation of free radicals (Abbaspour 2014))

C vitamins as well as B vitamins 9 & 12 help the function of Iron in the body, and can be found in… (Health Direct 2021; Mount Sinai; Harvard T.H Chan School of Public Health, Folate; Harvard T.H. Chan School of Public Health, Vitamin B12)

• Citrus fruits (C)

• Tomatoes (C)

• Berries (C)

• Leafy green veggies (C,B9)

• Beans (B9)

• Liver (B9,B12)

• Eggs (B9,B12)

• Fresh fruits (B9)

• Whole grains (B9)

• Milk, cheese, yogurt (B12)

• Nutritional yeast (B12)

While there are certainly other ways diet can impact the ANS, one more that is particularly worth noting is through the consumption of antioxidants. Antioxidants counter the destructive activity of free radicals (molecules that steal electrons, creating cellular damage) (Lobo 2010). Free radicals are a whole different topic to explore, but essentially, when free radical creation is greater than the defense capacity of antioxidants, the body goes into a state known as oxidative stress, which then increases sympathetic activity (Lobo 2010; Campese 2004). The best part is that antioxidants are not hard to come by (see High-ORAC foods)! You can find them in many fruits and vegetables (McBride 1999).

• Prunes

• Raisins

• Blueberries

• Blackberries

• Kale

• Strawberries

• Spinach

• Raspberries

• Brussel Sprouts

• And more!

Sleep

Sleep is key for maintaining a healthy, balanced autonomic nervous system. When we get a good night sleep (this includes continuity and duration) our heart beats with greater variability (Castro-Diehl et al. 2016). It would seem logical that having a heart that beats at regular intervals would be a sign of health. But that is actually not the case. Our body needs both the SNS and PNS to be in tip top shape if we are going to be functioning at our best, so it is constantly managing signals from both divisions. If the heart is beating at regular intervals it could mean that one system is not properly functioning. If it were receiving signals from both, then there would likely be a quicker heart rate at one moment when dealing with increased SNS activity, and a slower heart rate during another moment when dealing with more PNS activity (Whoop 2021). This would cause greater variability in the heart beating. The measurement of the difference between beats is called your Heart Rate Variability (HRV), and it can actually be found with your Apple Watch, Whoop, or other smart watch/ring you may already have (Harvard Health 2021).

In addition to potentially decreasing your HRV, a bad night's sleep can further hypoxic conditions in the body which would only exacerbate the excessive SNS activity already happening (Taylor et al. 2016).

If you do decide to start paying attention to your HRV don't let it be an absolute determinant of your health. See how lifestyle changes make you feel and if they coincide with a change in your HRV. As always, I am not a medical professional, nor an expert in any field, so what I write here does not substitute for medical advice, I merely put what I have found from reading research in the relevant areas.

Breathing

The easiest of the possibilities to promote parasympathetic activity is consciously breathing (deeply and slowly). The clear benefit of deep breathing is that you are taking in more oxygen than you would if you were breathing without intention. Deep breathing is also able to lower your heart rate and decrease stress which can be a sign of increased parasympathetic activity (Princing 2021; Russo 2017).

Meditation

Practices that require relaxation of the mind and body, as one may intuit, are responsible for reducing brain activity related to anxiety, but when it comes to the ANS there is not absolute consensus. There are some studies that suggest meditation is responsible for quieting sympathetic activity in the body (Kiran 2011; Bahrshankar 2015), and there are other studies that could not provide conclusive answers (Ganguly 2020; Telles 1993).

That being said, it is important to remember to do what works for you and makes you feel healthy, and at peace throughout your day, so do not let a couple inconclusive studies prevent you from exploring meditation (:

And obviously one big component of many meditative practices is a focus on the breath so there will also be that benefit should the meditation you do be a breath heavy practice.

Cold Exposure

This may be counterintuitive to some, as people typically associate cold with discomfort and stress. But with habituation to the cold, it is now being shown that the body is able to adapt; sympathetic activity can decline and parasympathetic activity can increase (Harinath 2005; Wim Hof Method Vagus Nerve Stimulation). If you are focusing on your breath and/or mindset in the cold you can calm yourself down, your body can begin to more efficiently regulate body temperature and even enter a state of relaxation. If cold exposure is a practice that is of interest then I would highly recommend checking out the Wim Hof Method (links to videos and resources will be down below), and starting by taking cold showers with a focus on relaxing the body and controlling your breath.

If you want to continue your exploration of these topics, check these out!

Oxygen levels and food

https://www.healthifyme.com/blog/foods-oxygen-levels/

Free radicals and antioxidants; simplified + easy to understand video: https://www.youtube.com/watch?v=HtF61dxP1zs

Wim Hof consciously activating sympathetic nervous system to combat sickness in supervised study:

https://www.youtube.com/watch?v=A6jqaALpEFM&t=5s