Most of her adult life, Sherry was busy doing for others. She was there for her friends, worked long hours when needed, was an endurance runner, and was the backbone of her family.
As she entered her 40s, she still did all these things but found herself irritable and not sleeping as well. Her long runs suffered. Her relationships suffered. And her resentment grew.
What Sherry didn’t realize was her nervous system had been changing from the time she was 30. And if she didn’t do something quick, by the time menopause showed up, she’d be a complete wreck.
I’s not her fault. Sherry never got introduced to her “new” post-40 nervous system. So, if you haven’t either, let’s meet her!
But first, let’s review some nervous system basics.
Autonomic nervous system 101
The central nervous system comprises nerve fibers that carry signals to and from our brain via the spinal cord to the rest of our body.
The autonomic nervous system (ANS) controls the involuntary functioning of the body, including digestion, sleep, breathing, heart and organ function and the ability to stay upright.
The ANS has two branches, including the sympathetic nervous system (SNS) known as the “fight or flight” response and the parasympathetic nervous system (PNS) controlled by the vagus nerve works to calm the body or “rest and digest.”
The SNS and PNS need to be in balance to keep your body in a state of homeostasis. These two opposing roles complement each other and, with optimal functioning, work together like a team.
You have a stressful event and the SNS fires up. But that means the PNS is right there to calm you back down.
Over time–and with aging and hormonal changes–the sympathetic part of the ANS becomes more dominate, throwing this balance off. And it happens sooner than we think.
Changes start after 30
Researchers determine sympathetic flow by measuring muscle sympathetic nerve activity (MSNA) burst frequency. In a group of 658 women and men, at age 20, it was similar in both groups.
Between 20 and 30 it decreased in women, reaching its lowest point 30. Although it climbed in both sexes at 30, the rate was higher for women. For instance, between the ages of 30 and 70 MSNA burst frequency tripled in women, but only increased by 50% in males.
I’m not sure why this is. Women have been found to have larger brain volume loss between the ages of 34-43, which could play a role.
But the key point is this rise in sympathetic activity happens at 30, well before changes in hormones occur, as stated by the authors:
The initial upward inflection in burst frequency was evident in both sexes at age 30. Since the average onset of natural menopause is ≈51 years, such timing excludes diminished endogenous estrogen concentrations as the principal responsible mechanism.
But because it takes time for this to accrue, many women don’t feel the effects until their 40s. Which is also the time perimenopause kicks in.
Along comes perimenopause
Our sex hormones, estrogen and progesterone, also help support vagal tone and the autonomic nervous system. So once they decline, it can be the tipping point for the ANS.
Menopause decreases heart rate variability (HRV), which is a measure of ANS. When your heart rate has a high variability, your ANS is adapting well to stressful events. When it’s low, it’s not recovering as it should.
Yet the effect of aging versus menopause is hard to disentangle, but there are clues that aging may be the more dominant factor.
To study the effects of estradiol on ANS function, researchers studied 41 healthy women (13 post-menopausal and 28 premenopausal). HRV measurements were taken at baseline and in response to an acute stress infusion.
Post-menopausal women had lower HRV compared to premenopausal women during their low estrogen phase of their cycle, but this significance disappeared when BMI and age were taken into account. Only the postmenopausal women exhibited a decrease in HRV in response to an acute stressor.
Yet there was no association between any measure of HRV and estrogen levels in premenopausal women. In fact, high estradiol in this group reduced HRV. The authors conclude:"
The findings of our study suggest that age, but not endogenous estradiol, is primarily responsible for the decrease in measures of HRV and unfavorable response to an acute stressor observed in postmenopausal women compared to premenopausal women.
According to a 2016 review menopausal hormone therapy may be supportive but when estrogen and progestogens are taking together, the effects are no longer seen.
The health impact
Think about what this nervous system imbalance does to the body. More sympathetic tone signals the body to “fight or flee,” redirecting blood to the muscles instead of the gut and other organs, and causing an increase in heart rate and blood pressure.
Chronically, this negatively affects the heart, sleep, and gut function. It also increases anxiety, sensitivity to pain, mast cell activity resulting in rashes and hives and hampers the immune system.
Because the vagus nerve plays a key role in the communication between peripheral organs and the brain, referred to as interoception, it has a substantial effect on emotional states.
For instance, low vagal activity can increase anxiety and depression, and researchers have found that vagal nerve stimulations improve treatment-resistant depression. Vagal interoceptive signals help us sustain emotional health.
And then there’s the risk of constant low-grade inflammation. An intact vagus nerve is vital for keeping inflammation at bay. And when it’s less effective, low-grade inflammation can become an issue.
This increases oxidative stress and lowers nitric oxide. Yes, it’s that One Health Principle again, where inflammation and oxidative stress increase and NO declines.
Vulnerable populations
Some women experience an exaggerated nervous system response. I should know because it happened to me.
Iron deficiency spiraled my anxiety out of control. Having low vitamin B12 does the same thing. Because of low red blood cell formation, these deficiencies stimulate sympathetic outflow, exaggerating a response already on the upswing, and decreasing vagal tone.
READ: Stand up for women: Make ferritin a screening standard
Just another reason we should be carefully monitoring these levels in women as they enter midlife.
Next is a history of trauma, including adverse childhood experiences (ACE). Women with higher ACE scores are at greater risk for an overactive nervous system and may find midlife particularly challenging.
Women experiencing chronic stress from caregiving, personal or financial hardship, or high-stress work environment are at higher risk, too. Chronic stress is like pressing the gas on an already vulnerable nervous system.
But have no doubt about it, all women are at risk. One study found that 67% of postmenopausal women before the age of 65 had ANS dysfunction.
Caring for your new nervous system
This news isn’t all bad. These changes literally force us to slow down and take care of ourselves.
With this new knowledge about her nervous system, Sherry could set new boundaries in her life and relationships and work to lighten her load. She also could try therapy to investigate why she is the person always there for others.
If you are in a vulnerable population, do what you can to get help. Of course, track your biomarkers to stay on top of iron and vitamin B12. But if you have a history of trauma, consider getting help. And if it’s a stressful time, ask for help from friends and family.
Finding ways to stimulate the vagus nerve and activate the parasympathetic nervous system is crucial for all of us. We have the power to reverse this!
One way is to incorporate slow breathing sessions most days. Researchers have found that practicing breathing at a rate of six breaths per minute increases HRV, and regularly practicing slow breathing can increase vagal tone.
HRV increases with other contemplative practices like yoga, time in nature, social connection, meditation, spending time with people you love, and let’s not forget laughing.
Staying hydrated is also important for increasing HRV and may be especially important as women transition through menopause.
Summary
Once we reach the age of 30, our autonomic nervous system starts to gradually increase sympathetic activity while decreasing parasympathetic (vagal) activity.
By the time we reach 40 years old, we usually start experiencing the effects that can lead to irritability, mood problems, difficulty sleeping, and anxiety.
The impact on the autonomic nervous system intensifies as we go through menopause.
Individuals with a deficiency in iron or B12, along with a history of trauma or chronic stress, may experience heightened effects.
This imbalance and decrease in vagal tone can become of source of low-grade inflammation, disrupting the One Health Principle.
Understanding this can help us develop new routines and ways of coping that support a changing nervous system. Examples include slow breathing, staying hydrated, setting boundaries, making sleep a priority and seeking help as needed.
We must consider our new nervous system when creating our midlife health routine. It’s just as important as exercise, diet, and other healthy habits.
It may not be one or two things we do, but the way we work with, instead of against, our new nervous system.
How is your “new” nervous system doing these days?
I am the same, wish I had known this instead of going through this experience blind!
Thank you so much for sharing this information x