# Menstruation and the Moon **URL:** \ **Category:** Factual Questions\ **Created:** [February 17, 2006, 10:23pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021 "2006-02-17T22:23:02Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [February 18, 2006, 10:57pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/21 "2006-02-18T22:57:42Z")
> [@smartie](#): > > And what “we” are all agreeing on is that there can be no connection between the moon and the body? Even for some women particularly prone to certain things? do i hear a yesyes? No, we can’t say there is “no connection” because we have no evidence of that. Proving the negative is a known impossibility of logic; you can only prove positive assertions. What you hear people saying is that there’s no evidence to support that this isn’t a coincidence while there’s plenty of evidence suggesting that it is coincidence. Further we are agreeing that humans are prone to spotting causation where none exists, that it’s been this way for thousands of years, and that it still happens today. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [February 18, 2006, 11:00pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/22 "2006-02-18T23:00:07Z")
> [@smartie](#): > > Okay dudes… okay… it is just coincidence that i menstruate on the full moon. okay. my little coincidence. let’s examine what other people have to say on this: > “Women’s periods have been tied to the moon and the lunar cycle for literally thousands of years. Before modern science came along to explain that a woman menstruates because of her changing hormones, it was generally accepted that a woman’s periods followed the lunar cycle.” [Menstruation: Your Menstrual Cyle and the Lunar Phase Fertility](http://www.epigee.org/menstruation_lunar_fertility.html) > > “It has been shown that calendar consciousness developed first in women because their natural body rhythms corresponded to observations of the moon. Chinese women established a lunar calendar 3000 years ago. Mayan women understood the great Maya calendar was based on menstrual cycles. Romans called the calculation of time menstruation, meaning knowledge of the menses. In Gaelic, menstruation and calendar are the same word.” [http://www.fwhc.org/health/moon.htm](http://www.fwhc.org/health/moon.htm) > > It is thought that perhaps moonlight had something to do with these cycles and since we’re less exposed today to moonlight, women are less in synch with the moon. Of course, there is or was no way every woman is always going to be in synch with the moon. It won’t happen. Too many variables. And what “we” are all agreeing on is that there can be no connection between the moon and the body? Even for some women particularly prone to certain things? do i hear a yesyes? Smartie, neither of those sources is a viable scientific source, and BOTH acknowledge that their “theories” are unproven. I understand that it’s a romantic notion that appeals to you, but the scientific fact is that 28 days just happens to be the place along the length-of-cycle scale that _Homo sapiens_ fell on. If a monthly cycle were more universal–hell, even more common–among other mammals–hell, just among other primates–the idea of their being a connection might make more sense. But such is not the case. The cycle had to be of SOME length, right? the fact that it happened to work itself out to 28/29 days is not in any way proof that it’s connected to lunar cycles. It’s only proof that the lunar cycle does not DISRUPT the cycle. We look for patterns. Often we find them when they’re not there. Else whence Las Vegas? ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [February 19, 2006, 12:30am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/23 "2006-02-19T00:30:08Z")
Why do I always shit in the morning? Is there something magical about the daylight cycle that causes my body to defacate at first light? I think it’s the sun’s mystical properties! Maybe if I rub my crystal, the postivie energy will rush into my brain and bless me with the answer… There must be something going on there. I mean, I shit EXACTLY every MORNING. And only sometimes do I not shit in the morning. So that’s undeniable proof right there! ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [February 19, 2006, 1:49am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/24 "2006-02-19T01:49:27Z")
> [@Brain Wreck](#): > > Proving the negative is a known impossibility of logic; you can only prove positive assertions. Ah, er, I don’t think so. It’s possible to prove quite easily that there cannot be two integers a and b such that a/b = √2. The method in that proof is to assume that it is true and then show that leads to a contradiction, a common method in proving negatives. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [February 19, 2006, 2:27am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/25 "2006-02-19T02:27:04Z")
> **[Menstruation: Your Menstrual Cyle and the Lunar Phase Fertility](http://www.epigee.org/menstruation_lunar_fertility.html)** > > An examination of how women's periods are linked to the cycles of the moon. From that same link: > [@](#): > > To the Moon > The theory of lunar phase fertility is generally credited to Dr. Eugene Jonas. In the 1950s, Dr. Jonas tried to find an explanation as to why so many women became pregnant despite faithfully practicing the rhythm method. The fact that these women were becoming pregnant at a time when they weren’t suppose to be fertile lead Dr. Jonas to reason that maybe women had more than one fertile period during a month. Since Dr. Jonas was very much into astrology, and since the original ways of charting a woman’s period were based on the lunar cycles, he turned his attention heaven ward. > > Not surprisingly, Dr. Jonas was met with quite a bit of skepticism from the medical and scientific world. Since his theory cannot be proven by modern-day scientific reasoning, many choose to dismiss the idea of having two fertile times as nonsense. As do I, **smartie** , as do I. > [@](#): > > Before modern science came along to explain that a woman menstruates because of her changing hormones, it was generally accepted that a woman’s periods followed the lunar cycle. After all, the moon controls the ocean, why not women’s bodies? Why not? And hey, while we’re why notting, why not have the eggs swirl clockwise above the equator and counterclockwise below the equator? After all, don’t toilets flush that way? So why not women’s bodies? From your other link: [Menstrual Cycles: What Really Happens in those 28 Days?!](http://www.fwhc.org/health/moon.htm) > [@](#): > > Have you ever wondered about the connection between your body’s 28 day cycle and the cycle of the moon? Here’s the theory. In the days before electricity, women’s bodies were influenced by the amount of moonlight we saw. Just as sunlight and moonlight affect plants and animals, our hormones were triggered by levels of moonlight. And, all women cycled together. Today, with artificial light everywhere, day and night, our cycles no longer correspond to the moon. How convenient. But wait: doesn’t that mean that tribes where women don’t use electricity should still be affected? Ta da! Something we can test scientifically! Except they don’t bother. > [@](#): > > Every woman’s cycle is or should be 28 days long. > Every woman will or should bleed every month. > Every woman will or should ovulate every cycle. > If a woman bleeds, she is not pregnant. > A woman cannot ovulate or get pregnant while she is menstruating. > The above statements are myths. Every woman is different. But if cycles aren’t 28 days long, how can they correspond to the moon? In short, even your own cites show that tying menstrual cycles to the moon is romantic astrology, and are not susceptible to science. Or to reality. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [February 19, 2006, 2:40am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/26 "2006-02-19T02:40:56Z")
> [@RM Mentock](#): > > The moon revolves around the Earth, on average, every 27 1/3- days–it goes through the complete zodiacal cycle each time. However, the time between full moons is on average 29 1/2+ days, as others have pointed out, because of the earth/moon revolution around the sun. > > (The length of the year divided by the full moon cycle is 365.256 / 29.531 = 12.369, so there are a little over 12 moon cycles per year. We lose a cycle because of the revolution of the earth/moon around the sun, which is why 365.256 / 27.322 is 13.369, exactly one more.) This post proves, at least to my satisfaction, that the supposed connection between the moon and menstrual cycles is folklore. 1. The average mentrual interval reported by Cecil is 28 days. 2. The period of the moon as seen from the earth’s surface is the thing that would influence menstual intervals. 3. The period of the moon as seen from the earth is 29½+ days. In light of 2) and given that Cecil is correct, statements 1) and 3) are incompatible with the idea that the moon influences the menstrual cycle. ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [February 19, 2006, 3:36pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/27 "2006-02-19T15:36:12Z")
> [@David Simmons](#): > > Ah, er, I don’t think so. It’s possible to prove quite easily that there cannot be two integers a and b such that a/b = √2. The method in that proof is to assume that it is true and then show that leads to a contradiction, a common method in proving negatives. OK, maybe my way of stating the principle needs some refinement. How would you use that method to prove conclusively that you aren’t a member of the communist party or that the Invisible Pink Unicorn doesn’t exist? That’s the kind of thing I’m talking about. Maybe my way of stating the principle needs some refinement. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [February 19, 2006, 5:19pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/28 "2006-02-19T17:19:33Z")
> [@Brain Wreck](#): > > How would you use that method to prove conclusively that you aren’t a member of the communist party or that the Invisible Pink Unicorn doesn’t exist? That’s the kind of thing I’m talking about. Maybe my way of stating the principle needs some refinement. It’s difficult to prove that you didn’t do something, but not always impossible. For example you can demonstrate that it is highly unlikely that you were robbing a gas station in Podunk on 15 February at 11:00 AM by gathering witnesses to your having at that time been in Cornstalk 50 miles away giving a speech to the Rotary Club. However it is difficult to prove that you didn’t do something, such as join the Communist Party, which is why the burden of proof is not on you but rather on the person or group making that claim that you did. And your statement was “Proving the negative is a known impossibility of logic” and your examples here are about matters of fact, not logic. **smartie’s** claim is about a matter of fact. Are or are not her mentrual cycles exactly coincident with the full moon? She can demonstrate that to herself and us by keeping a log for long enough that the statistics of the sample are representive of her whole menstrual history. However, even that wouldn’t prove causation because, all together now and not too loud - Correlation does not prove causation. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [February 19, 2006, 9:25pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/29 "2006-02-19T21:25:54Z")
> [@](#): > > For 30 years my cycles have been regular as clockwork - on a 32 day cycle. So I never match a lunar cycle. For 30 years. Well, you sometimes match a lunar cycle. Once every few years, if your cycle is that regular, you’re guaranteed to menstruate on the same day as the full moon. ---
**Author:** ![irishgirl](https://avatars.discourse-cdn.com/v4/letter/i/8edcca/32.png) [@irishgirl](https://boards.straightdope.com/u/irishgirl)\ **Post date:** [February 19, 2006, 10:03pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/30 "2006-02-19T22:03:49Z")
If you have a perfectly regular 29 day cycle you have a 1 in 29 chance of the first day of menstruation co-inciding with the full moon…or the new moon, or in, fact, any other point in the lunar cycle. If you actually want to be _properly_ romantic about the whole thing, your _ovulation_ would coincide with the full moon, since that is the point when you are most fertile and the uterine lining is thickest, your period would co-incide with the new moon, when the uterine lining is thinnest. Then the waxing and waning of the moon would exactly co-incide with the waxing and waning of your endometrium. **smartie** , for future reference, when one of the Mods links to a Cecil Adams article that disagrees with you, you aren’t going to find a lot of people on these boards willing to back your point of view. ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [February 19, 2006, 10:18pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/31 "2006-02-19T22:18:19Z")
**smartie** , you are [Kate Bush](http://www.alwaysontherun.net/kate.htm#ac) and I claim my £5. > [@](#): > > Soon it will be the phase of the moon > When people tune in. > Every girl knows about the punctual blues, > But who’s to know the power behind our moves? ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [February 19, 2006, 11:14pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/32 "2006-02-19T23:14:15Z")
> [@jjimm](#): > > **smartie** , you are [Kate Bush](http://www.alwaysontherun.net/kate.htm#ac) and I claim my £5. But even KaTe stops short of making a direct link between the moon and menses. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [February 20, 2006, 8:48am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/33 "2006-02-20T08:48:21Z")
> [@Chronos](#): > > Well, you sometimes match a lunar cycle. Once every few years, if your cycle is that regular, you’re guaranteed to menstruate on the same day as the full moon. I wouldn’t call that matching a lunar cycle, though. It’s being at the same point of the cycle–but that can happen every cycle, just at another different point of the cycle. The other monkeywrench is that the time between full moons is not constant. The 29 1/2+ days is an average. For instance, I see that the last full moon was 04:44 UT Feb. 13, and the next is 23:35 UT Mar. 14, which is 29.785 days. So someone with a perfect 32 day cycle might be able to avoid even that match. ---
**Author:** ![FlyingRamenMonster](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@FlyingRamenMonster](https://boards.straightdope.com/u/FlyingRamenMonster)\ **Post date:** [February 20, 2006, 1:15pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/34 "2006-02-20T13:15:18Z")
It seems you already know what you want to know. So why are you asking us? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [February 20, 2006, 7:09pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/35 "2006-02-20T19:09:59Z")
Maybe this has already been said in one form or another, but I didn’t feel like re-reading all the posts. But this would be like saying that my wrist watch is effected by the earths rotation. Or that the rotation of the earth is effected by my clock. Not the case, just becuase they have the same period (hehe) doesn’t mean they are influenced by each other. ---
**Author:** ![Youbetcha](https://avatars.discourse-cdn.com/v4/letter/y/b19c9b/32.png) [@Youbetcha](https://boards.straightdope.com/u/Youbetcha)\ **Post date:** [February 20, 2006, 7:47pm UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/36 "2006-02-20T19:47:20Z")
A little experiment… When my wife was my long time girlfriend and she was living with 6 other women she and her roomates did several experiments to test a bunch of theories about their cycles. I was asked to be the impartial data collector, though being a man I was told by one roommate that I couldn’t possibly be impartial and I had a vested interest in how this all turned out so I was watched very closely. The two main ones were that women living together tend to get their periods in sync with each other over time (because of the hormones they can smell on each other?), and that their cycles were related to the moon cycle somehow. We gathered data for almost two years. There were two strong believers of both moon and roommate theories and I think the rest were ambivalent. They had all definitely at least heard the theories previously. There were two women on the pill who had fairly regular 28 day cycles. Unfortunately the moon’s cycle in 29+ as discussed previously so they weren’t much good for the experiment. One of them was a strong believer in the moon cycle even though she was on the pill. Now with 7 women in the house many of their periods overlapped and they had cycles ranging from 26 days to 34 days for the non pill users. The non pill users had fairly regular cycles though they could be out by a day or two of their average each month. For short periods of time some of their cycles would ‘sync up’ but obviously go out of sync again. Their periods would occassionaly sync up with the moon cycles as well but not for long. What they gathered was that they all noticed when they did sync up (with each other or the moon) but they didn’t really pay much attention when they weren’t synced. Sort of a self fullfilling theory. Oddly enough even though she was part of the test one of the women still believes both theories! She saw it with her own eyes on paper with the moon cycles and how she wasn’t syncing with the moon or her roommates but didn’t believe it for various reasons. She was blaming the other two roomates taking the pill for all of them not syncing up! It has definitely been romanticized and unfortunately theories like this can be hurtful. If a woman strongly believes the theory but is not in sync at all they can get depressed about it for example. anyhow…just 2 cents + of personal experiment ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 24, 2006, 3:43am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/37 "2006-02-24T03:43:12Z")
> [@Youbetcha](#): > > A little experiment… > > When my wife was my long time girlfriend and she was living with 6 other women she and her roomates did several experiments to test a bunch of theories about their cycles. [Do the menstrual cycles of women living together tend to synchronize?](http://www.straightdope.com/classics/a2_306.html) ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [February 24, 2006, 4:15am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/38 "2006-02-24T04:15:54Z")
> [@Cecil Adams](#): > > The corresponding estrus cycles of some other mammals are 28 days for opossums, 11 days for guinea pigs, 16 to 17 days for sheep, 20 to 22 days for sows, 21 days for cows and mares, 24 to 26 days for macaque monkeys, 37 days for chimpanzees, and only 5 days for rats and mice Look, maybe it’s just me, but I am thunderstruck. It is reasonable to expect that an animal with a **5 day estrus cycle** such as a rat should be a difficult animal to be around. No? Imagine it. A 5 day cycle. Damn. No wonder rats like chocolate so much. ( ducks, runs, leaves Hershey bars behind ) A reasonable hijack is to ask if any female astronauts have been in long-term orbit long enough to have had their cycles altered? If lunar pull has nothing to do with cycles, does gravity? Cartooniverse ---
**Author:** ![outlierrn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/outlierrn/32/3005_2.png) [@outlierrn](https://boards.straightdope.com/u/outlierrn)\ **Post date:** [February 24, 2006, 4:54am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/39 "2006-02-24T04:54:04Z")
I was asked to be the impartial data collector, though being a man I was told by one roommate that I couldn’t possibly be impartial and I had a vested interest in how this all turned out so I was watched very closely. [/QUOTE] seems to me you could make a case for being the most impartial person in the house. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [February 24, 2006, 6:17am UTC](https://boards.straightdope.com/t/menstruation-and-the-moon/345021/40 "2006-02-24T06:17:44Z")
On the concept of women sychronizing their menstruation, I have some **anecdotal** data. At the end I’ll try to weigh the pros and cons. For a few years, I was the restroom janitor for an office building attached to a factory. There were separate trash cans in each women’s restroom for used feminine products, and I’m pretty sure I was the only one who emptied them. There were over a hundred women working in there. The entire building shared a single forced air heating-cooling system. The menstrual trash, collected daily, was always greatest in the week before a full moon, and scarce in other times. On the pro side: Not only did all the women share the ventilation, but they all used the same restrooms, where the menstrual by-products were thrown away. Consciously or not, they all got a whiff of the heavy week. All the women shared the same air for 8 hours a day, 5 or 6 days a week. The women were unaware anybody was observing the evidence of their cycles. On the con side: Some of the women were surely post-menopausal, so they were not in the sample. Some of the women were probably on BC pills, which would lock in a 28 day cycle. Statistically, the sample was fairly small. Only the one data point was observed. None of the women was interviewed about age or hormone use. So, is this a useful set of data? Maybe, maybe not. [Previous page](https://boards.straightdope.com/t/menstruation-and-the-moon/345021.md?page=1) [Next page](https://boards.straightdope.com/t/menstruation-and-the-moon/345021.md?page=3)