Is it your understanding that only hormone levels fluctuate throughout the menstrual cycle? Well, I have news that might change your mind. Hormones aren’t the only bodily component that follows a monthly rhythm.
In October 2023, a research study out of the University of California, Santa Barbara (UCSB) found that the entirety of womens’ brain structure actually fluctuates throughout the menstrual cycle as well. As an undergraduate student attending UCSB, I had the privilege of interviewing Elizabeth Rizor, a dedicated PhD student who worked on this study.
As we sat down amidst the hum of UCSB's bustling campus, Elizabeth shared a rare glimpse into this relationship between hormonal health and brain structure. We also discussed how this research could redefine our current understanding of womens’ health in areas like menstrual symptoms and exercise.
To start, I asked Elizabeth to help us understand the body parts and processes that were tracked — specifically brain matter and the female hormonal cycle.
There’s lots of gray area in our brains — but even more white area.
The building blocks of our brains are gray and white matter. Gray matter is typically where most of the focus goes, since it's responsible for daily functions like controlling movement, memory, and emotions. Gray matter is the outer layer of the brain, and as Elizabeth described,
“is like a cortical ribbon that goes along the edge of the brain. Gray matter is where functional activation is happening. It’s where the cell bodies [of brain cells or neurons] are really clustered.”
About 40% of the brain is gray matter, while the other 60% is white matter.
If white matter makes up over half of our brain, then it must also have a pretty important role.
Why is white matter white?. Myelin wraps around the axons of brain cells which are the long cable-like connections between cell bodies. Myelin helps speed up the rate that electrical signals travel across the brain. When white matter is compromised, this can affect sensory, motor, and cognitive functions (basically the ability to sense, move, and think).
Elizabeth described white matter to be
“fatty tissue underneath the outer layer of gray matter that consists of bundles of axons. You can think of it kind of like bundles of straws, or highways that transmit information between the different brain regions in the gray matter. It can perform this long range cross-communication between different areas in the brain.”
It seems that white matter is the vital medium for messages to be sent across different parts of the brain. If these areas are changing, this could imply changes in communication. The potential impact of this on womens’ cognition, emotion, and overall brain function is still being investigated.
What has been observed is that white matter changes across hormonal transition phases like puberty, taking birth control, menopausal treatment, and gender transition treatment — however, there is a lack of research exploring standard, baseline hormonal and brain changes across a natural menstrual cycle.
Elizabeth Rizor and her colleagues noticed this lack of research in naturally cycling young women. Women make up half of the population, and nearly all women naturally cycle for decades of their lives.
Discoveries related to this brain-hormone connection have implications for a drastic portion of the population.
So, what are the study details?
The study included thirty women ranging between 18 to 29 years old (21 being the average). The average length of these womens’ cycles was 31 days.
The hormones they tracked are a part of the HPG axis — HPG standing for Hypothalamic - Pituitary - Gonadal, and axis refers to how these organs span across the body. Brain scans and hormone levels were analyzed at three time points throughout the menstrual cycle: Menses, Ovulation, and Mid-Luteal.
So, what did they find?
After all of the brain scans and blood tests collected, the researchers found that follicle stimulating hormone (FSH) and progesterone had a see-saw relationship. FSH had moderate levels during menses and was high during ovulation. Progesterone was higher during the luteal phase, which is the other end of the cycle. This didn’t surprise the researchers.
However the big shocker, as Elizabeth explained, was that
“both white matter and gray matter had an opposing tension between the two hormones. Where one [hormone] was correlated with change in white matter, and the other correlated with the opposite. The same occurred in the gray matter and cortical thickness [width of gray matter cortical ribbon] as well.”
What's the impact of this?
While this study didn’t explore brain structure impact on cognition across the cycle, the cyclical changes in brain matter may infer cognitive advantages for one phase versus another. Phase-dependent brain changes could also provide explanation for differences in emotional processing, cognitive performance, and motivation throughout the menstrual cycle that are worth future investigation.
More and more research has found differences in attention, memory, and verbal and spatial skills throughout the cycle. However, studies on PMS and PMDD have only looked into changes in executive function and attention.
This work can be used as a baseline in furthering our understanding of menstrual disorders such as premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD). Some women with these disorders have reported "difficulty concentrating and impaired work productivity" during the late luteal phase.
More and more research has found differences in attention, memory, and verbal and spatial skills throughout the cycle. However, studies on PMS and PMDD have only looked into changes in executive function and attention.
Executive function is how thoughts, emotions, and actions are managed and controlled. This aspect of the brain allows for planning, achieving, and problem solving. If there is a change in these functions, the ability to perform daily activities could be affected.
Brains, Bleeding, and Bloating — How can women use this knowledge of brain and hormonal changes to understand menstrual symptoms?
I asked Elizabeth if there were findings from the study that surprised her.
“For some of the individual findings, you can see some people trend opposite of the group.”
This observation reveals that biometrics and symptoms don’t always align with what is considered “normal”. As Elizabeth said,
“Everyone has different emotional and cognitive experiences. There’s a lot of individual differences throughout your experience of the cycle and hormone fluctuation.”
However, if you think you might have PMDD (Premenstrual Dysphoric Disorder) or other menstrual difficulties, the consultation of healthcare professionals is advised to evaluate whether you are suffering from deeper brain or hormonal imbalances. The symptoms you experience are worth paying attention to, not just ignoring or suppressing.
Rizor shared personally about her own experience as a naturally cycling woman and the pressure she felt from herself and others to ignore her cycle symptoms:
“Throughout my life, I didn’t think critically often enough about my menstrual cycle, just that it was a kind of nuisance I had to deal with. I also felt pressure to stay normal and perform the same every single day. What I think our study does well, as do some other studies, is that it literally shows there are baseline anatomical changes that are fairly consistent across a group of around 30 women.”
And, these changes do not exist in isolation.
“These hormones are circulating in the blood throughout your entire body, so they’re not just going to be affecting your reproductive organs, or your abdomen. These hormones cross the blood brain barrier, going into the brain. There could be other effects on other organs as well — so it’s really a whole body process.”
There is reassurance remembering we don’t have to feel alone in our experiences — tuning in and recognizing our symptoms can provide opportunities to connect with others. There is no shame in experiencing these symptoms. Our task is to figure out how to understand these changes to figure out what our bodies are telling us.
“We can all experience our own symptoms and be used to having them in our day-to-day lives. On certain days during my PMS phase, I get more moody and bloated. But I think we often feel that we’re so individual and alone in our experiences. But you don’t actually know if — if you don’t talk about it — what other people are also experiencing. You might not make the link that these things are happening because of baseline biological processes.”
Brains, Bleeding, and Bench Press — How can women apply this knowledge of brain and hormonal changes to exercise routines?
Because brain and hormone changes could affect the whole body, one might consider how these changes inform other health areas. Changes in executive functioning and other menstrual symptoms may influence the daily activities and health goals we have — including exercise.
Cycle dependent exercise routines are a trendy topic on social media. The impact of brain changes and hormonal changes on motivation, visual, and spatial perception, social media accounts and exercise programs may recommend specific exercises for certain cycle phases.
Here’s what Elizabeth had to say on the subject:
“There are recommendations out there to do certain exercises during certain phases of your cycle, but there’s no one answer for everyone. It’s more about what works for you — except for the health basics, like drink water and sleep. But when it comes to exercise, it’s definitely more nuanced.”
Instead, Elizabeth recommended pairing baseline knowledge of your biology with tuning in to your body’s signals. This can help you gauge what movement you’re actually craving, instead of disconnecting more by adhering to strict and generalized fitness routines:
“If you have this understanding of the cycle as a rhythm and pulse cascading throughout your whole body, affecting your brain and many different areas, then you can be more understanding and kind to yourself that you might want to tweak your routine.”
Elizabeth instead recommended pairing this baseline knowledge with tuning in to your body’s signals. This can help you gauge what kind of movement your body is craving, instead of further disconnecting by adhering to strict and generalized fitness routines:
“If you have this understanding of the cycle as you know, a rhythm and a pulse that’s cascading throughout your whole body and affecting your brain and affecting all these different areas, then you could be more understanding and kind to yourself that you might be up for or you might want to tweak your routine.”
Conclusion
With all of the conflicting health information available online — it’s easy to get lost and confused about what to do. What Elizabeth and her fellow researchers at UCSB are discovering, is that women have natural biological fluctuations. These fluctuations may correlate with differences in how our bodies feel throughout the month. Instead of continuing to disconnect and place generalized expectations on ourselves, let’s tune back in and give our bodies what they actually need — a listening ear and response to its signals.
