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This episode is the 2nd edition of a podcast I did a while back on the menstrual cycle. I review the stages of the cycle, what causes menstruation, what happens if conception occurs, and update you with some new information we’ve learned since the last episode came out.
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00:00:00
Chris Sandel: Welcome to episode 165 of Real Health Radio. You can find the links talked about as part of this episode at the show notes, which is www.seven-health.com/165.
Welcome to Real Health Radio. Health advice that’s more than just about how you look. Here’s your host, Chris Sandel.
Hi everybody, and welcome back to another installment of Real Health Radio. So there’s two bits of housekeeping this week before I get on with the show. The first is to let you all know that transcripts are now available for the podcast. I’d mentioned this in a PS on one of my emails a couple of weeks ago and on a Facebook post, but I haven’t yet mentioned it on the show.
This is something that’s been requested for a long time now and I know personally there are times when I simply want to read rather than listen to an episode. This is especially true if it’s information-dense, if I’ve already listened to the episode and I want to go back and find something that was referenced. So each week when a new episode comes out, the transcript will be available. We’re also setting something up so you can download the transcripts as a PDF.
I’m not sure if that’s going to be done by the time this episode comes out, but it is coming. We’ve also gone back and added transcripts for the more recent episodes, so going back to I think episode 162. That now obviously leaves 161 podcasts that still need to have transcripts created for them. When I check my iTunes, this works out at roughly or over six days of audio. I think it’s around 150 hours, so it’s no small task.
To start with, we’re going to look at the podcasts that have the most amount of downloads and use this as a guide as well as probably preferencing the solo episodes because they’re often more information-dense and often work better to read than the conversation ones. So that’s the plan and it should take a few months for them all to be done.
00:02:30
The second bit of housekeeping is to do with the fact that Weight Watchers or the company formerly known as Weight Watchers, I think they’re just going by WW now, have released a dieting app for children called Kobo. This is for children as young as eight and up to 17 years. I think this is a disaster of an idea and that’s pretty mildly. I have a lot of things to say on this topic, but I think I’m going to save it for a separate episode, but what I do want to make people aware of is there is a petition on change.org that I’ll link to in the show notes.
Let me just quickly quote from that page to give you a tiny sense of why this app is such a bad idea. “Eating disorders have the highest mortality rates of any mental illness. Every 62 minutes at least one person dies as a direct result from an eating disorder. This app will literally kill people. According to doctors, adolescence is a critical period of development and a window of vulnerability during which eating disorders can develop. Pediatric eating disorders are more common than type 2 diabetes. In 2016, the American Academy of Pediatrics advised doctors and families to steer clear of weight talk and instead focus on emphasizing healthy lifestyles.”
As I said, I will put a link to the petition in the show notes. If you are as outraged about this as I am, you could sign up and hopefully, something will come of it. Now on with today’s show. This week’s show is another solo episode and it’s actually a second edition podcast. So this is me doing an update of a podcast that I previously recorded, and the podcast is called The Female Menstrual Cycle, and it was originally released back in the 23rd of June, 2016.
00:04:00
Like my recent edition of the podcast or the recent second edition of the podcast on Understanding Carbohydrates, probably about 50% of this podcast is either new material or sections that had been heavily edited at points, where I’ve added in new chunks of content, or I’ve removed sections of information or make reference to it. I’ll explain why I’ve done this and if it’s just simply adding in or removing a single line, or a single thought, then it’ll just happen without me mentioning it.
Honestly, there is a lot that we don’t know about the menstrual cycle and even reproduction more generally. It’s funny when we look back a hundred years or 200 years and we see what we used to believe and think how naive and incorrect we were in so many ways. Well, we are still in that place. Like in 50 years, in a hundred years, we’ll look back at where we are now and think how backward we were and how wrong we were about certain topics.
Just to demonstrate how true this is, in 2013, two Belgium surgeons found a new ligament in the body that hadn’t been discovered before. It was connected to the knee, and if you think about how long we’ve been looking at the anatomy of the body and how many surgeries has been done on the knee, then if we discover a new body part in 2013, then that says something about our understanding of the body.
It would not surprise me at all if we discover some new hormone or some new receptor or neurotransmitter that is hugely important as part of the female menstrual cycle or that hormones that we already know of, that we don’t associate with menstruation actually turn out to be an important part of it. What I’m going to go through as part of the show is by no means a definitive guide on how menstruation work. Partly, this is because of gaps in what we know, but also because of the audience that this is aimed at. I want you to walk away from this episode understanding enough to help you in your life, not so you can go and teach a physiology lecture on the menstrual cycle to medical students.
That said, this is still probably going to be more on the technical end of things. This episode is mostly about the organs and the hormones and the physiology that is involved throughout the cycle, with a focus on what is happening when it’s working as it should be, with a little bit of a focus on what happens when this is oft. There’s going to be many hormones and organs that are very familiar to me, and I’m used to talking about and hearing about, but that’s not going to be the case for everyone.
While I’m trying to make this as accessible as possible for the lay public, like I imagine some people are still going to find this difficult to follow. If this is the case and it would make it easier than try reading the transcript, and you can find that at www.seven-health.com/165.
As a side note, I actually did a podcast before on the reasons why a woman may be having issues with their cycle. Looking at the causes connected to when things go awry, it’s episode 25 of the podcast, and I’ll link to it in the show notes. It was recorded three and a half years ago. In time, it will also be getting a second edition, but if you’re interested in that now, you can still check it out. I would say I’d still mostly agree with what I included as part of it.
To start with, I’m going to break the menstrual cycle into little small parts so you can understand it and then I will put it all back together and talk about the bigger picture.
00:07:45
To start with, let’s go through the organs that are involved in the menstrual cycle. First off, we have the ovaries, and there’s two of them, and the purpose of the ovary is to produce an egg.
We have the uterus and what is most important for the episode isn’t the uterus per se, but the build-up of the blood, and the nutrients that occur on the uterine wall known as the endometrium. This is where the egg is going to implant itself if it becomes fertilized, and the embryo then starts growing. Around the egg as it is developing, there is a large layer that surrounds it called the follicle. This gets built up during the menstrual cycle. It’s worth keeping in mind the word follicle, as when we get onto the hormones, one of them is called follicle-stimulating hormone, and then you can remember that this is what it’s stimulating, like it’s stimulating the production of the egg.
As a side note, it is the same in male reproduction, where the sperm is known as the follicle and men produce follicle-stimulating hormone just like women do. The final organ isn’t really an organ, but is a tissue called the corpus luteum. It’s produced after ovulation. As the follicle ovulates the egg is released into the fallopian tube and what remains is now called the corpus luteum. This doesn’t appear until the latter part of the menstrual cycle or the second half of the menstrual cycle, and is the sac-like organ that used to hold the egg. The follicle that used to hold the egg before the egg came out of it.
00:09:25
Now moving on to the hormones that are involved as part of the menstrual cycle. For each, I’ll give a bit of a description of what they’ll do and then I’ll pull this together more when we look at the big picture of how things work and how things change through the cycle. The first hormone is called gonadotropin-releasing hormone. This is produced in the hypothalamus, which is a section of the brain and is released in a pulsating fashion.
One of the hypothalamus’ job is to monitor the level of certain hormones and certain substances in the blood, and then make changes that lead to other hormones going up or down depending on what is needed. While this podcast is about the menstrual cycle, the hypothalamus isn’t just about reproduction, so it deals with many facets of physiology. One of the big roles that hypothalamus plays is regulating how much food you eat, and the kinds of foods you crave, as well as things like body temperature, sleep, thirst, so hugely important. When those other things are off, this can have an impact on what happens with the menstrual cycle.
The hypothalamus releases gonadotropin-releasing hormone, which is recognized by the pituitary. This is another gland also located in the brain. The gonadotropin-releasing hormone stimulates the pituitary to produce two hormones in relation to reproduction. These two hormones are follicle-stimulating hormone, also known as FSH, and luteinizing hormone, also known as LH.
Follicle-stimulating hormone helps the follicle in the ovary to grow as the name would suggest, and luteinizing hormone aids the egg in maturing and then it’s also needed to trigger ovulation and the release of the egg from the ovary.
But luteinizing hormone and follicle-stimulating hormone also play a role in stimulating other hormones that are important to reproduction. The luteinizing hormone and follicle-stimulating hormone go into the bloodstream and they go down to their target organ in the hormone system, which is the ovaries. This then stimulates the ovaries to produce two more hormones. One of these is estrogen and the other one is progesterone.
Estrogen has many roles in the body, both for reproduction and outside of reproduction. For today, I’m just going to focus on its reproductive qualities. Estrogen is involved in the onset of puberty, playing a role in the development of so-called secondary sex characteristics, so things like breast and pubic and armpit hair. Once a woman is getting her cycle, estrogen helps build the growth of the uterine lining especially in the follicular stage, which is the first half of the cycle.
Estrogen is also important for ovulation, which I’m going to talk about in a minute. Progesterone like estrogen has many reproductive and non-reproductive functions. So when looking at the reproductive side of things, progesterone helps with the growth of the uterine lining, especially in the luteal phase or the second half of the cycle. It prepares the uterus for implantation by causing changes to the endometrium.
If we go through the flow of hormones again, you’ve got gonadotropin-releasing hormone that is released from the hypothalamus, which then stimulates the pituitary, the pituitary then produces two hormones; follicle stimulating hormone and luteinizing hormone. These hormones then travel in the blood down to the ovary and stimulate two more hormones, estrogen and progesterone. There are other hormones that are involved in this process that we know of and probably others that we are yet to learn about, but these other hormones I’m going to focus on for today.
00:13:20
When talking about the menstrual cycle, there are three main stages. The first is the follicular stage, the second is ovulation, and then the third is the luteal phase. Let’s start with a very stripped back explanation of each of these and then we can get into more detail. On average, the menstrual cycle takes about 28 days. It can be shorter or it can be longer, but for this example, let’s just assume that it is 28 days.
So day zero or day one through two 14 is known as the follicular stage. It’s called this because this is the stage that’s really concerned with developing the follicle. The follicle includes the egg and the outer sac that is housing the egg both of which grow over this time. At around day 14 on average, the follicle ovulates, it ruptures and outcomes the egg into the fallopian tube. Then this leaves behind the remanent or sac, which is known as the corpus luteum, and we now enter then the luteal phase, which is from day 14 through to day 28.
This phase is really about building up the uterine lining in preparation for implantation if conception actually occurs. If conception doesn’t happen, then menstruation occurs and we go back to day one of the cycle, so start of the follicular phase. That’s an overview. Let me just add in more details and then explain how the different hormones work and are doing different things at different times. I would say that this would probably be easier if there was a visual aid that you could look at while I’m talking about this stuff, but we’re on a podcast, so that’s not going to happen. So I’ll just do my best so you can understand it.
00:15:00
From day zero to day 14 is the follicular stage. Just so you know, like day one is the first day of a woman’s period and then goes on from there. While a woman is having a period, the body’s already underway with preparation for the next egg. The egg in the follicle is getting bigger and bigger and growing from day one onwards. I really should say follicles and eggs because it’s not just one, like the ovary actually produces many follicles in the first part of the month, and then typically around day five, day seven there, it has become like a dominant follicle known as a Graafian follicle. This one will then continue to develop to the point of your ovulation while the others get reabsorbed and they disappear.
Actually, the development of the follicles takes much longer than this. This is something new to this episode that I’m adding in. Follicles go through this very long development process. Starting out, you have what is known as a primordial follicle, and it actually takes at least 270 days to go from a primordial follicle to develop and change to what is known as a preantral follicle.
This preantral follicle then continues to grow and this takes place over about 75 days. This then takes you up to the start of that follicular phase, so day one of the cycle. Then over the next 10 or so days, a follicle will continue to develop, and then finally around the midpoint, it will actually ovulate.
All of these figures I’ve stated here come from a paper that I will link to in the show notes. It was from 1986, so maybe our understanding has changed somewhat and these figures have now been adjusted. But even if there has been some changes, I would imagine that the general idea is the same.
The reason why this is important is to show how long this process really is. It takes over a year to go from primordial follicle to being ovulated. So what you were doing over a year ago can be impacting on your cycle now. And considering I work with many women who have lost their period, this is especially important. Because even when your period comes back, there’s still a backlog of about a year from what you are doing today from where it’s going to be affecting the primordial follicle until the point it reaches ovulation.
During this process, I should also add, there’s this huge attrition. I don’t know what the exact figure is, but the estimate that I’ve seen bandied around is that at the point of a woman reaching puberty, they have around 400,000 ovarian follicles. How many time a woman ovulates throughout her life would be dependent on many factors. It’s hard to give an exact figure on this, but it’s somewhere in the realm of 900 to 1,000 primordial follicles to have one that then reaches ovulation.
Now back to the hormones. The reason for the development of the follicle is really follicle stimulating hormone. Over the first 10 or so days, it’s slowly increasing, therefore stimulating the follicle to also grow. During this time, luteinizing hormone is being produced, but its production for the first 10 to 12 days is fairly constant. So it’s helping with egg maturation, but a much more reduced way during this time.
But it’s then around day 12 that we have something interesting happen. Luteinizing hormone has been traveling at that constant level, but suddenly you get this large spike. This spike can last anywhere from 24 to 48 hours, and this spike causes the egg to completely mature and for the membrane of the follicle to become thinner before it finally ruptures with the egg coming free, and making its way into the fallopian tube.
Now, what has caused, this is probably only partly understood, but what we do know is that an increase in estrogen is part of it. At day one of the cycle, estrogen is basically at its lowest point of any time during the 28 days, and during a woman’s period, estrogen is still pretty low, but it’s starting to come up. But once the old uterine lining has been shed, the body has to then get back to making a new one just in case this is then going to be the month that conception happens.
From about day four to day six, estrogen starts to climb, and this increase starts to build up the new endometrium. Part of the reason that this estrogen is rising is that is produced by the developing follicle. As the follicle is increasing in size because of the follicle stimulating hormone, so is the level of estrogen that is being produced. This is part of the reason why women who aren’t ovulating, say with hypothalamic amenorrhea or HA, may have lower levels of estrogen.
Yes, estrogen is produced from the ovaries, but a lot of this is connected to the follicles that have been developed on the ovaries. So when this isn’t happening then estrogen is going to be lower or could potentially be lower. But when things are working as they should be, estrogen continues to increase as the follicle develops. Then estrogen hits some decisive point, roughly around day 12 or so. This almost turns on a switch with the luteinizing hormone. We then see that it peaks sharply as I’ve already mentioned, which then causes ovulation.
So you have an increase in estrogen that leads to an increase in luteinizing hormone, which then leads to ovulation. In fact, there’s a peak in all the hormones prior to ovulation. There is a peak in follicle stimulating hormone and there’s also a peak or an increase in progesterone, although in real terms, the progesterone increase is fairly minimal, but it does appear that the increase in progesterone seems to be necessary for ovulation. So really it is a combined effort of all these hormones working together.
As I mentioned earlier, the follicle turns into the corpus luteum after ovulation. For the first couple of days after ovulation, the corpus luteum actually grows quite quickly and increases in size. While the follicle was under the influence of follicle stimulating hormone in the first half of the cycle, during the second half when it has now become the corpus luteum, its growth is largely influenced by the luteinizing hormone. That rise in luteinizing hormone that then creates the ovulation isn’t only important for ovulation, but also for the couple of days following because it then increases the size of the corpus luteum.
00:22:15
Why this is important is due to progesterone production, the one hormone that I really haven’t talked that much about so far. Progesterone is very much a hormone concerned with the luteal phase or the second half of the cycle if we’re talking about it as a reproductive hormone.
I know earlier I mentioned that the ovaries produce both estrogen and progesterone, which is true. But the production of this progesterone for the cycle is mostly down to the corpus luteum, which is attached to the ovary. Progesterone’s rise in the second half of the cycle is almost entirely down to the corpus luteum and because of ovulation.
If ovulation doesn’t occur for some reason, an increase in progesterone doesn’t happen to the same degree in the second half of the cycle. After ovulation and in the couple of days just immediately after, the corpus luteum is rapidly increasing and progesterone production is also rapidly increasing. Part of the reason for this increase is to continue the production and the maintenance of the endometrium. Because if we look at the endometrium wall during the cycle, estrogen helps to build it up in the first half of the cycle. But after ovulation, estrogen levels drop down fairly rapidly almost to the level at the start of the cycle. Then it takes another four or five days before they start to increase again.
If the endometrium was solely being nourished and protected by estrogen, then this could be enough to trigger menstruation at the midpoint of the cycle. But it doesn’t. This is because, after ovulation, the corpus luteum takes over and starts producing progesterone, and the progesterone continues to produce and increase the uterine wall.
Interestingly, this could be a possible explanation for why some women get mid-cycle spotting or bleeding. If estrogen drops down and then progesterone is still too low and is taking longer to increase, then this could lead to the shedding of some of the uterine lining, but once the progesterone levels increase enough, then this stops.
00:24:30
After dropping down at the midpoint, estrogen starts to increase again in the second half of the cycle. This is somewhere around day 18 or 19, if we’re using the 28-day cycle as an example. The reason for this increase, again, is the corpus luteum. Just like the follicle was producing estrogen in the first half of the cycle, the corpus luteum is producing estrogen in the second half of the cycle. The corpus luteum produces not just progesterone but also estrogen as well.
After a couple of days in the luteal phase, so the second half, luteinizing hormone drops rapidly, and the corpus luteum slows its growth and then it stops. At this point, things can then go one of two ways. One is menstruation, and then two is conception. Let’s look at menstruation first.
00:25:15
Now that luteinizing hormone production has stopped, the corpus luteum stops growing, and despite this, it continues to still produce progesterone and estrogen and continues to maintain the endometrium wall. But after about 10 days, if conception hasn’t occurred, the corpus luteum starts to degenerate and to decay. It then degenerates into the corpus albicans, which is a tiny, massive, like fibrous scar tissue.
With this degrading and then the disappearing of the corpus luteum, progesterone production starts to sharply decline. This happens around day 23. Estrogen levels also start to decline, this is maybe a little later around day 24 or day 25. Because estrogen and progesterone were the hormones that were maintaining the endometrium, there is now nothing left to stimulate the support to the structure. When these hormones then drop lower and then reach some baseline level, say around day 28, the endometrium begins to break down and we get menstruation, which is the shedding of the endometrium.
00:26:30
Now, if conception had actually occurred, this process would have gone down a different direction. If a sperm comes in contact and then fertilizes the egg, we now start to see a new hormone that I haven’t mentioned before now, and this hormone is called HCG, which stands for human chorionic gonadotropin, much easier to just call it HCG. This is the hormone, the little dipstick or the pregnancy tests test for. When you’re on it, this is what they’re looking for. The purpose of this hormone is that it takes over the role of luteinizing hormone, and it maintains the corpus luteum.
HCG is a luteinizing hormone analog, meaning it binds to the same receptors and then it does a similar thing. It then stimulates the corpus luteum to continue to grow to persist to increase the progesterone so that you then maintain that endometrium wall. The fertilized egg then hopefully continues down the fallopian tube and makes its way into the uterus and then can implant onto that endometrium wall.
The corpus luteum does the role of stimulating that progesterone production for roughly the first trimester. After this, its role is taken over by the placenta. But this is often the reason why you can have a miscarriage around this time because the corpus luteum starts to degrade, but the placenta hasn’t taken over properly. It can also be part of the reason why women start to feel better from the second trimester onwards because that placenta can be able to produce more progesterone or just that switch tends to make or can make women feel better. So there it is. That is the very basic stripped back version of how the menstrual cycle works. You probably now know more than the general population.
00:28:30
Let me add some further points. The first thing I want to mention is actually a correction from the original episode that I did. Let me just read out what I had originally stated. “The menstrual cycle is not always 28 days as it should be. For some it can be every three weeks, for others it can be five or six weeks, and while the number of days can fluctuate, the second half of the cycle is normally constant. So meaning from the point of ovulation to when someone gets their period, it’s fairly consistently 14 days plus or minus a day or two. This means that if someone is having a three-week cycle, they are typically having a shorter follicular phase or first half of the cycle with minor changes to the second half. If someone is having a five-week cycle, then they’re typically having a longer follicular or first half of the cycle with only minor changes to the luteal or second phase. So it’s normally that luteal phase or the second half that is more constant and the follicular phase or the first half is what gets shorter and longer.”
That is the gist of what I said in the original show. This information or that information had come from Dr. John Lee. I’d read a number of his books at the time. He is, or was, I’m not sure if he’s still alive, a gynecologist in the U.S., he was a big proponent of progesterone therapy, so using bioidentical hormones, and he’s probably a pioneer in this field. I originally came across him because of my interest in Ray Peat and Ray Peat making reference to him, and given Peat’s rather contrarian views, Lee may be thought more as a rogue doctor than a pioneer. I’m not really sure. It’s been a while since I’ve read his material.
But the reason I’m wanting to make this correction is because for the women that I often see in practice, who’ve had their periods stop through underrating and through over-training, whether that be because of an eating disorder or whether that be because of disordered eating, or read as, when it does come back, they will often have a shorter second half of the cycle or luteal phase. This has a rather unflattering name of luteal phase defect.
For the women that I see, when they are getting their cycles back, even if they are having long cycles, it can be that from the point at which they ovulate, there’s like seven or eight or nine days before they then get their period. When I am working with these clients, and they’re paying attention to their cycles, we’re looking at what is happening with this second half and seeing how long it is. Like, “Is it roughly 14 days? If it is shorter than this, like what is happening then cycle on cycle. Is this luteal phase increasing? Is it going from eight days to nine days to 11 days and so on?”
Because it can take quite a few cycles for this to improve, so we’re seeing, “Is this going in the right direction?” Now, I’m unsure of how much of an issue this is within the general population. I know for fertility issues or infertility issues where couples are failing to get pregnant or having miscarriages, luteal phase defect is talked about as an issue. So it’s obviously not just people getting their period back, but I’m just unsure about how true Dr. Lee’s comments are. Is it the case that in most women who are having regular cycles that the second half of the cycle is mostly set in stone and is around 14 days, or is it that what he said is just incorrect?
Honestly, I do not know, but I want to mention this and make this correction from the original episode, especially because of my audience and knowing that many will fall into the category where having a shorter luteal phase is likely.
00:32:30
Another point that I want to make, and this was in the original episode, but I’m going to greatly expand on it here, is that just because a woman gets her period doesn’t mean that she’s ovulated. Unless follicle stimulating hormone is doing what it should do, and then there’s this surge of estrogen and luteinizing hormone and ovulation, if those things don’t happen, ovulation doesn’t occur. When these things fail to happen, but a period happens, it’s known as an anovulatory cycle.
I actually wrote an article about this recently on my blog, which I will link to in the show notes. Now, an anovulatory cycle can be something that is happening on its own, or they can be part of some other issues. Say with polycystic ovary syndrome, where these other combinations of factors are at play. If we’re thinking of the hormones that are talked about or that I talked about earlier, there are a couple of things that could be going on that lead to anovulatory cycles.
What I’m going to outline here is more from what I’ve seen in clinical practice and from my understanding of how these various hormones work. I don’t have any papers to support this, so if you want to think of this as speculation, you can. If someone is in their 20s or their early 30s, and this is happening, you possibly see low levels of luteinizing hormone and estrogen and potentially follicle stimulating hormone, and this is going to lead to the endometrium being built up but thinner and lighter, follicles developed, but again, probably at the lesser end of things, so more immature follicles.
Then when there is the spike of hormones that should produce ovulation, the amounts just don’t get high enough. So it follows the usual pattern, but the peak isn’t high enough and so ovulation doesn’t occur. This then means that in the second half of the cycle, progesterone is much lower because there isn’t the corpus luteum that greatly increases that production. Then at some point, because conception hasn’t occurred, the progesterone and the estrogen drop down to levels that menstruation occurs.
This is what I would think would be most likely happening if anovulatory cycles are occurring for someone at a younger age. Now, if someone who is older especially as they’re approaching menopause, it could be more likely that you’re going to have luteinizing hormone and follicle stimulating hormone that are higher in the first half of the cycle. So the baseline numbers are higher. The reason that this is happening is because these hormones aren’t having the effect that they should.
Luteinizing hormone and follicle stimulating hormone are part of a feedback loop. The body produces them to stimulate the growth of the follicles, but it wants to do this in the right amount. If it takes a certain amount to do this job, the body doesn’t want to be producing double or triple of this amount. There’s a feedback that goes on to tell the body that it’s producing enough of these hormones, that these hormones are increasing follicle production. And then because of that feedback the follicle production is happening, the body tells these hormones to stay at the levels that they’re at, that it doesn’t need to go any higher.
But as somebody’s reaching menopause, the luteinizing hormone and follicle stimulating hormone stop being so effective. The feedback that these hormones then get is that, “We need more of you to do the job.” So their baseline levels start to increase. It’s like if someone has a hearing impairment and it’s getting worse with age, if they’re watching television, they have to turn the volume higher to be able to hear it. Luteinizing hormone and follicle stimulating hormone in this instance is like the volume.
In this scenario, estrogen might be normal but it’s potentially low because if the luteinizing hormone and the follicle stimulating hormone isn’t doing what it used to be able to do, then the estrogen, which is largely produced by the developing follicle is also going to probably be reduced. Then everything else is the same as how I talked about in the first example. Like there’s the spike at the midpoint, but not enough to trigger ovulation. Then there’s low amounts of estrogen in the second half of the cycle because there’s no corpus luteum to produce it. Then at some point you get the period.
That’s the two potential options for how this could work. Anovulatory cycles aren’t the only reason for short or long or irregular cycles, but they’re just something to keep in mind. A clue of this could be having light periods because without the ovulation and with the potential lower estrogen and progesterone production, the endometrium hasn’t built up as much as it ordinarily would.
I should say also that my comments in this episode are in regards to someone who is not on some form of hormonal contraception. If someone is on hormonal contraception, like the pill, the whole point is to create anovulatory cycles. Like, they work by creating high levels of estrogen and/or progesterone or whatever hormone is in the pill. In a sense, the body thinks that it is already pregnant. Because of this, it prevents the luteinizing hormone spike that then stimulates ovulation.
For someone on the pill, when they are bleeding at the end of the cycle, this can be more thought about as a pill-bleed rather than menstruation. The bleed happens because for a handful of days, the pill that is being taken doesn’t have any hormone in it. For the first 21 days, the pills contained whatever hormones are being used, whether that be estrogen, and/or progesterone, and then there is a week of inert placebo pills. When the hormone stop coming in, the levels drop and then there’s nothing to support the uterine lining, and so menstruation occurs.
00:38:30
Something I haven’t mentioned is around the levels of various hormones. I mentioned earlier about an article I wrote recently about anovulatory cycles. During that article, I made reference to some research that looked at this, which I’ll link to in the show notes. The figures used in the article are based on research that was done in 2006. The study used a sample of 20 females, aged between 20 and 36 years old, with normal cycles and no use of hormonal contraceptive.
As part of the study, hormone samples were taken every day during the cycle. This 2006 paper was then reanalyzed in 2014. As these figures that were then created they were then based on what I’m going to be linking to in the show notes and what I’m making reference to here. What they’ve done when looking at this is to look at the four main hormones; estrogen, progesterone, luteinizing hormone, and follicle stimulating hormone, and to plot it out across each day of the cycle.
You can see the pattern that each of these hormones follows across a cycle, so when they go up, when they go down, when they spike, et cetera. But what’s great about this is how they’ve then been separated out to take into consideration variability. There is a line that tracks the average throughout the cycle, so when they look at all the women, what is the average on each day, but then they also include these much wider areas, which are above and below the average line to show different bands of ranges.
One of these is looking at how things differ because of biological stage. For example, one person may ovulate on day 12 and another may ovulate on day 15. This means that on each of these days these individuals are going to be affecting different hormone levels. This graph has to make sense for both of these situations and all the different options.
You have this wider band that includes biological stage. Then there’s a band that looks at inter-cycle variability, also known as within-woman variability. This is looking at, “If we followed the same woman cycle after cycle, how much would her hormones change between cycles?” Then finally there is an inter-woman variability, which is the variability when we compare one woman to another woman and do this across multiple cycles. How much variability is there in the population or at least the population of 20 women?
These extra bits of information are really helpful because it allows you to see how much variability naturally occurs. Because if there was just this one average line and then someone was above it or below it, you wouldn’t know if this was completely normal to expect, or if this was something that needed attention and worth investigating.
One thing I would say about this research in terms of leaning on the numbers too heavily is due to the small sample size. This only included 20 women. I’m currently reading The Undoing Project by Michael Lewis. You may know Michael Lewis from other books he’s done that had been turned into movies, so things like Moneyball and The Big Short. The Undoing Project is about the work of Amos Tversky and Danny Kahneman. They’re two psychologists who looked at how humans make decisions and the biases and the heuristics that lead to human errors.
Even if you don’t know their names, you’ve undoubtedly been exposed to or even read books that wouldn’t have been written if it wasn’t for work of these guys. Kahneman actually won the Nobel prize for economics in 2002 because of this work. If Tversky hadn’t died already, they would have won it jointly.
One of the others that they identify is using a small number to make big predictions. It talks about how psychologists used to use a sample of around 40 people, but actually, this would only give about a 50% chance of accurately reflecting the population. To have a 90% chance of capturing the traits of the larger population, the sample size would need to be at least 130.
Making too big an assumption based on 20 people could mean that these results aren’t representative of the population or even representative of the population that we’re trying to study, which is women who are having normal cycles, who aren’t on oral contraceptive pill, between the ages of 20 and 36. Statistics definitely aren’t my strong point, so I could be wrong on this, but if I’m not, it is just something to keep in mind.
I need to thank Nicola Rinaldi for pointing me towards this piece of research from 2014. She originally did a blog post about it back in 2017. I’m going to quote Nicola’s article about how this can be helpful.
“One example of when I might refer to these figures is if someone tells me that they’ve just had blood drawn, but they don’t know what cycle day they’re on, so e.g. if they’ve not yet had their first post-hypothalamic amenorrhea period or their first postpartum period. If we say luteinizing hormone was measured at 17, and estradiol, so estrogen was at 215, I can check these figures and see that this is most likely corresponds to just before ovulation. If luteinizing hormone is 17 and estrogen is 85, that might mean that ovulation has just occurred. If luteinizing hormone is 17 and estrogen is 30, then I might suggest inducing bleed and testing a hormone panel to determine if PCOS might be at play. I think what is unique and particularly helpful in these figures, is an inclusion of variability, so one has an idea of the typical range for these hormones.”
I also should say that I’ve used Nicola’s book, No Period. Now What? to update some of the bits of information in the earlier sections. When I went through the various hormones and when I did the original episode, I wasn’t aware of Nicola, so in this episode, because I have her book and it is such a wonderful resource, I wanted to see what areas needed updating and use that book. If you’re listening, Nicola, thank you for all that you do.
00:45:00
That is it for this week’s episode. I know that I mentioned lots of different hormones and organs you may not have heard before. Even if that was the case, I hope I was able to explain it in a way that you’re able to follow along and that you now have a better understanding of the menstrual cycle. If it was a little technical, you can go and read the transcript and see if that helps.
Next Thursday, I’m going to go away, and I’m away for a week. So there will be no new podcast next week, but there will be a rebroadcast episode. I will be back with a new episode shortly. Until then, take care of yourself.
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