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Progesterone and Vagal Tone


I remember being told in one of my women’s yoga trainings that progesterone impacts vagal tone, and I was curious because I’d never heard this before, so, me being me, naturally I decided to do some research!

 

This is what I learned about the complex relationship between stress, the vagus nerve, and progesterone.

 

First, what is the vagus nerve and 'vagal tone'?

 

The vagus nerve is the longest nerve in the body (also known as cranial nerve 10), connecting the brain to the gut (as well as other organs). It’s like a superhighway, sending signals to and from the brain throughout the body, and is a key part of the parasympathetic nervous system. We now understand that the vagus nerve can become ‘dysregulated’ (often due to trauma or chronic stress) leading to ‘poor (or low) vagal tone’. Vagal ‘toning’ essentially means helping to regulate or support our nervous system, and to become more resilient to stress. High or increased tone means better resilience and nervous system regulation.

 

Progesterone is one of the main sex hormones, responsible for maintaining a pregnancy (by maintaining the uterine lining). You might have heard of progesterone referred to as the ‘calming hormone’. This is because progesterone is metabolised into allopregnanolone, which in turn enhances the effects of GABA – a neurotransmitter known for its calming effect on the body, essentially acting like a brake pedal to slow down neuronal activity, reducing anxiety and promoting relaxation (and therefore better sleep).

 

Yet, interestingly, progesterone also decreases vagal tone. This means less parasympathetic (rest and digest) activity and more sympathetic activity (fight or flight response). This could theoretically cause more anxiety or mood changes, and could make it harder to get into the parasympathetic state (i.e. make it harder to relax).

 

In other words, our bodies are extremely complex! And, often, hormones (and other health topics!) don’t fit into neat little boxes that make for a good social media sound bite!

 

But, what does all of this mean for you and your cycle?


Shortly after ovulation, when progesterone is at its highest in your cycle, you might find that you’re sleeping better and have less anxiety. At the same time, however, since progesterone reduces vagal tone, you might notice that your resting heart rate is higher than usual, and your heart rate variability (HRV) is lower (if you usually measure these with an apple watch or Oura ring, for example, it would be interesting to note for yourself if you see these changes!). For some women, this might also mean that it’s harder to relax or switch off.

 

In the 2nd half of the luteal phase (the week before your period is due), when progesterone decreases, you might find that your sleep quality worsens or anxiety heightens (this is when many women experience PMS symptoms, including mood swings and poor sleep). While low progesterone means that it’s not there to lower vagal tone, unfortunately, oestrogen is also low in this phase (and oestrogen tends to increase vagal tone). So, this is when it’s especially important to rely on other tools to help tone the vagus nerve (such as singing, humming, diaphragmatic breathing, and so on).

 

It seems that ultimately, progesterone’s effect on vagal tone doesn’t detract from its separate action on GABA, so overall it can still be said to be a ‘calming hormone’. But, now you know why progesterone might also be lowering HRV and raising your heart rate (both of which are sometimes associated with stress or lower resilience).

 

If you’d like to know more about hormones, women’s wellness and nutrition, check out my free webinar, and make sure you're following on social media for more nutrition and hormone health content.

 

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