Every day, your hormones are orchestrating a silent symphony in your body. Insulin, which regulates blood sugar, constantly adjusts to your diet and energy needs. The stress hormone cortisol peaks in the morning and declines with the sunset; melatonin does the opposite and lulls you to sleep.
For those who menstruate, another concert is tacked on top. Each of the four phases of the menstrual cycle is dictated by a spike or fall of hormones like estrogen, follicle-stimulating hormone (also known as FSH), luteinizing hormone (or LH), and progesterone. While reproduction is the primary focus of this monthly chemical crescendo, we know the menstrual cycle influences and is crucial for various physiological processes, from bone health to mood regulation.
But there’s a lingering question often overlooked when we consider the menstrual cycle’s intricate chemical web: How exactly does it affect the brain? This may feel like a question straight out of the bygone era of female hysteria and biased cultural notions surrounding menstruation and behavior. However, emerging research suggests our brains could be reshaped by the menstrual cycle, such as getting bigger during parts of it or gaining a cognitive boost during ovulation.
A study released last week on the preprint server bioRxiv is fleshing out this hormonal dance quietly shaping the brain. Looking at the brains of 30 young, healthy people during different stages of their menstrual cycle, researchers at the University of California, Santa Barbara (UCSB), found that levels of certain hormones matched changes in the brain’s white and gray matter. For example, ovulation’s characteristic surge of estrogen and LH coincided with potentially beneficial changes in white matter, the communication highways of the brain. Peaking levels of FSH between menstruation and ovulation appeared tied to the thickness of neural tissue making up the cerebral cortex, called gray matter.
“With this study, we’re providing further evidence that these [reproductive] hormones… are not only at the core of understanding processes like stress and health but also — at the risk of sounding cheesy — what makes us us every day of our lives,” Viktoriya Babenko, one of the study’s first authors formerly of UCSB, tells Inverse. “The details of those ways are yet to be solidified because there’s so little research, but they could have implications not only for hormonal treatments like contraceptives” but other health disorders and conditions affected by reproductive hormones as well.
Fluctuations reshaping the brain
Scientists have been studying the menstrual cycle and its effects on physiology and behavior since the 1930s, not purely for its own sake but to understand what makes women biologically different from men.
“The majority of the present-day scientific knowledge and clinical practices have been attempting to mold female biology into a male framework,” says Babenko. “The consequences to [those who menstruate] have really been extensive, including a higher likelihood to be misdiagnosed, given an inappropriate dosage of medication, or experience adverse side effects from those medications.”
While it’s recognized that the ovaries, uterus, and brain share a neurological connection, there have been far more studies examining the effects of reproductive hormones on cognitive and brain function, not nearly enough looking at how these hormones directly affect brain anatomy in real-time, says Babenko and Elizabeth Rizor, one of the study’s first authors and a graduate student in UCSB’s Psychological and Brain Sciences Department.
“Our lab specializes in employing advanced neuroimaging or MRI methods,” Rizor tells Inverse. “We thought we could expand upon this research by really focusing rigorously, bringing in people and taking blood draws to [measure] their hormone concentrations and doing these structural MRIs that we think can provide a clearer look at white and gray matter structure than before.”
For their study, the researchers recruited 30 college-aged individuals between the ages of 18 and 29 who, by their account, had normal, regular menstrual cycles.
The participants came into the lab three times during the early, mid-, and late stages of their menstrual cycle. Before entering an MRI machine, the researchers checked their levels of four hormones: 17-beta-estradiol (the main form of estrogen in the human body, which regulates the menstrual cycle, supports reproductive tissues, and influences bone health, mood, and various metabolic processes); progesterone (prepares and maintains the uterine lining for a fertilized egg to implant and supports early pregnancy); FSH (stimulates the growth and maturation of eggs in females, as well as sperm production in males); and LH (triggers ovulation in females, but testosterone production in males).
“The majority of the present-day scientific knowledge and clinical practices have been attempting to mold female biology into a male framework.”
Babenko, Rizor, and their colleagues saw that as the hormones fluxed throughout the menstrual cycle, different structural changes materialized. When estrogen, LH, and FSH peaked during ovulation — the period when a mature egg is released from the ovary typically two weeks after the first day of a person’s menstrual cycle — there were changes in the participants’ white matter, potentially indicating better communication between neurons, although it’s hard to say.
“We’re looking at measures that some people consider to represent white matter connectivity or integrity, but they basically just tell us that there are changes happening within the white matter of the brain,” explains Rizor.
The gray matter at the cortex of the brain also got thicker, particularly in response to FSH, which peaks and plummets right before ovulation. Progesterone, which is secreted by a mass of cells that form in the ovary called the corpus luteum right after ovulation, seemed to encourage thicker gray matter in some parts of the brain but decreased in others.
What’s next?
Whether these changes indicated a boon or hindrance to the brain isn’t yet clear, say Babenko and Rizor. This study is part of a much larger project examining the menstrual cycle’s influence on stress, cognitive behavior, and other aspects of well-being, and we may get answers as that research progresses. But these changes aren’t likely to be harmful in any way and potentially temporary, says Babenko, ebbing and flowing with the cyclic nature that is the menstrual cycle.
It’s also not easy to say whether these changes are a result of a single or the entire ensemble of hormones — that is to say, if it’s solely estrogen instigating white matter changes, only LH, only FSH, or any number of combinations.
“We’re just saying there’s a correlation with this hormone; there’s no way that in this type of study, we can extract that being in combination with other hormones,” says Babenko. “I think it comes down to different concentrations can have all sorts of different effects on the body, and you can’t just distinguish them apart from each other when you’re looking at a human being as a whole.”
Such research might be possible in the future and could lend powerfully important insight into revolutionizing or improving contraceptive methods, which remain predominantly hormonal. It could also lend insight into a slew of gynecological conditions like dysmenorrhea or painful periods. (Rizor says some studies have found gray matter changes associated with experiencing more pain during periods for some individuals.) Estrogen has been show to increase seizures, so further research could also help in the area as well.
Editor’s Note: An earlier version of this story misspelled Elizabeth Rizor’s last name in two instances. In both, it was spelled as Rizvor, when it is, in fact, Rizor. The earlier version also referred to Rizor as a graduate student in UCSB’s Neuroscience Department when she is actually a graduate student in UCSB’s Psychological and Brain Sciences Department.
