Okay, let's have a look at the paper I posted the other week
, which claims to have shown that "Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the Moon
Introduction and 'facts'
1. “In many marine species and some terrestrial species, reproductive behavior is synchronized with a particular phase of the lunar cycle (often full or new moon).”
Seems reasonable. Nine references cited. Though I notice the ninth one is a study I’ve come across before claiming a connection between the lunar cycle and birth rate in cows
. It used a very small sample size (428 cases) whereas a much larger study involving a few million births
showed no pattern. I wrote to one of the authors of this study a year or two ago and pointed out the flaws in their methodology and conclusion, but they stuck to what they believed their own data showed them rather than the data from the largescale study (understandably).
2. “It is of interest that the human menstrual cycle has a period close to that of the lunar cycle.”
I mean, not really. Number one “the human menstrual cycle” has a ‘normal’ period of between 21 and 38-40 days, whereas the lunar cycle is much less variable (+/- ~0.3 days) so there’s not really a similarity. The average menstrual cycle is around 29 days, which is close to the average lunar cycle of 29.53 days – but so what? If the average human male is 5 feet 9 and the average horse is 5 feet 10, does that suggest the two are somehow related?
3. “Several older studies report a relation between the [two] cycles.”
Some bad studies
do report a relation. As discussed above, Cutler’s studies being the prime example, and these are cited repeatedly throughout the paper. When I messaged Helfrich-Förster about these studies she admitted that she hadn’t looked into them closely, which – when coupled with the dubious citation noted in point 1 – doesn’t bode well for the other references used. Cutler’s studies are excellent examples of terrible science and, to her credit, Helfrich-Förster agreed with the issues we raised here.
Furthermore, the biggest and best studies – the Clue study
, for example – find zero relation.
4. “In these studies, about 28% of reproductively mature women showed a cycle length of 29.5 ± 1 days. Among populations of women selected for a cycle length of 29.5 ± 1 days, a significant pattern of menses onset at full moon emerged. Each of these studies comprised >300 women, and the tests were performed in different years and seasons.”
Figures from Cutler, therefore irrelevant and not a good way to start your paper. “>300 women” is an insignificant number and it’s surprising that academics with a good understanding of statistical analysis wouldn't pick up on that. Far too small a sample size to detect a “significant pattern” – which there wasn’t in those studies in any case.
5. “Significant correlations also appear to exist between birth rate and moon phase.”
Absolutely untrue. Again, some small scale and methodologically dubious studies are cited, whereas the two largest studies – that of Caton and Wheatley (2002)
and the one I did here
(together comprising 155 million births) – found no correlation whatsoever.
(This paper seems to have primarily taken as ‘proof’ for the “significant correlations” the three studies done by Menaker and Menaker from the 50s and 60s. None of the studies agree with one another, and the deviation from the mean was tiny
(1-3%) – which, of course, is about what we would expect given the randomness of nature.)
6. “Effects of gravity might account for the fact that synchrony of sleep onset and sleep duration with the lunar cycle has been observed in college students living in the light-polluted city of Seattle, where the Moon’s luminance cycle is scarcely perceivable.” (from later on in the paper)
Maybe. Not sure. https://advances.sciencemag.org/content/7/5/eabe0465
7. “Bipolar mood cycles have been reported to oscillate in synchrony with either the full moon phase or the new moon phase of the Moon’s luminance cycle.”
An interesting paper here related to that: https://www.nature.com/articles/mp2016263
. But I haven't looked into it, and it's probably too new an idea with too little research done to confirm or deny.
8. “Several studies including ours have shown that night light shortens the length of the menstrual cycle.”
I don’t know about the reliability of this claim. FatPhil above posted a link to a study that claimed to show that night light regulated
the length of the menstrual cycle (though for some it lengthened). Very possible that the light was applied in a different manner, though.
9. “The scientific community generally remains skeptical of reports of lunar influence on human biology.”
I believe the scientific community – or, at least, those who have an interest and have looked into it properly – would go further than that, and state with confidence that there is no reason
to believe that the moon has an influence on human biology, and that all evidence points to this not being the case.
Still, it’s always good to be open to the possibility of being proven wrong in something like this – but, unfortunately, this has not been a good opening for the paper.
1. “We examined the course of menstrual cycles in 22 individuals who kept long-term records of menses onsets. This approach allowed for the possibilities that lunar influence might be present intermittently and in different forms over the females’ life. Furthermore, in our study, we tested the Moon’s gravitational influences on menses onsets, in addition to its nocturnal light effects. To our knowledge, this approach to the evaluation of such long-term data has not been used previously.”
Yes. Excellent idea. An unfortunately small sample size, but it was difficult for them to find sufficient women who had kept long-term records.
2. “[Some basic facts about the lunar cycle; and] when the Moon is at its perigee and simultaneously in Moon-Sun-Earth syzygy, the gravitational forces on Earth are very high.”
The gravitational forces exerted on an individual human, however, are tiny: my laptop is probably applying more gravity to my body than the moon is, no matter where it might be situated in relation to Earth.
3. "We found that all three lunar cycles—the synodic, the anomalistic, and, to a lesser degree, the tropical month—affect menses onset.”
Steady on. That seems a bit like jumping to conclusions – especially with such a small sample size, and with such a shaky beginning. Let’s look at the data first…
4. “Nocturnal moonlight appears to be the strongest zeitgeber through which the Moon exerts its influence. We hypothesize that in ancient times, human reproductive behavior was synchronous with the Moon but that our modern lifestyle, notably our increasing exposure to artificial light, has changed this relation.”
Interestingly, that’s the get-out clause that moon-loving women use when I point out that their belief in the menstruation-lunar connection is flawed (even, usually, by their own data and experience). But Strassmann’s studies showed no lunar connection in people who lived as “in ancient times” and had no exposure to artificial light (Strassmann curiously not cited here).
5. “To determine whether menses onsets were ever synchronous with the lunar cycle, we analyzed the relation of menses onsets to the full moon and the new moon, to minimum and maximum lunar standstills, and to lunar perigees and apogees for each individual.”
Cool. Now we’re getting to the data. And I do like their approach: take the onset dates over the course of a long period of time and plot them against what the actual moon was actually doing. It’s a novel approach that should reveal something other larger scale studies potentially miss in bunching huge numbers of women of all ages together.
What I find most interesting to look at are the charts that show exactly when
a woman began her period plotted against what the moon was doing at the time. For example, for 6 of their 22 subjects:
This shows, for example, that Subject 1 had prolonged timespans where her menstrual cycles were approximately 29.5 days in length several times in her life: in 1979/80 (aged ~22); in 1998 (~41); and between 1999 and 2003 (aged ~42-46). These are designated by the yellow and blue arrows (there are also occurrences in 1991, 1996, and 2010, but these seems a little short).
The apparent significance here is that not only were these incidences of regular cycle lengths of the same duration as the lunar cycle, but that they only occurred on the full or new moon, and at no other times in the lunar cycle - ie, the vertical straightish lines formed by the black dots are uniquely aligned to either the full or new moon.
Looking at four of the other five subjects, the same is also claimed. Subjects 2 and 3 have long periods of being 'aligned' with the full moon (ages 19-27 and 27-31 respectively), and a few proposed shorter periods in later life, while Subjects 4 and 5 have less clear 'patterns' and shorter timespans of 'alignment' - though what clusters they do have, again, seem only in alignment with the full/new moon and don't occur in other parts of the synodic lunar month. Subject 6, however, doesn't seem to exhibit any signs of 'synchronization'.
Charts for 8 more subjects are provided (those who kept records for several years before 35 years of age):
In the authors' own words "Subjects 8 and 11 [...] did not show any synchronization to the synodic lunar month", while it appears to me that Subject 9 showed a decent alignment with the full moon aged 26-27 and 26-37; Subject 7 around age 28; and Subject 15 around age 16. The rest have claimed periods of alignments - as pointed out by the arrows - but they seem quite weak.
For the remaining 8 of the 22 subjects, either their charts weren't included because they didn't exhibit any semblance of conforming to the pattern or I'm completely missing mention of them, despite looking through the paper several times (not impossible).
Therefore I guess what we have is 6 subjects who were 'aligned' with the full/new moon for prolonged periods of time (and not with any other day of the lunar month); 5 who could be claimed to have some sort of 'alignment' (if you squint a bit); 3 who didn't; and probably another 8 who didn't either.
I guess the crux is: how can we explain why, when these women did have prolonged periods of 29.5-day menstrual cycles, did they only ever correspond with a full or new moon? Is "chance" or "small sample size" a satisfying enough answer? I'm not sure it is.
It strikes me that, were the onset dates plotted against different cycles lengths - eg, 26 days or 32 days - we would also see prolonged periods of "vertical black dots". This seems that it would be true given the large number of uniformally-sloped diagonal lines in the charts above (indicating prolonged periods of cycles longer or shorter than 29.5 days). According to the paper, however:
“A systematic test with different hypothetical lunar cycle lengths ranging from 27 to 32 days showed that the significant results for the a priori hypothesis of synchronization with the full/new moon did not emerge by chance.”
I'm surprised by this. But will have to think about it more.
The tropical cycle
They felt this had less of an effect than the synodic cycle, so I won't look at that.
Saros #137 eclipses
The paper states that:
"There were four episodes, in the second halves of 1961, 1979, 1997, and 2015, in which seven of nine women’s menstrual cycles oscillated in synchrony with the synodic month (blue shaded areas in the charts above). The 18-year interval between these years corresponds to the period of a cycle of lunar eclipses that occur in September at those years, called Saros series #137. Saros #137 eclipses are distinguished by the contemporaneous occurrence of perigees that are unusually close to Earth. The conjunction of these two events may have augmented the Moon’s strength as a zeitgeber."
And I'm not sure what to think about that.
Either I lost focus after this or the paper did. There was a claim that menstrual cycles synced with the gravimetric lunar cycle, but I couldn't see it in either the data or the charts, so maybe you can:
Yellow diagonal lines = apogee and grey = perigee (green vertical lines = maximum lunar standstill and pink = minimum).
1. “The synodic lunar cycle alone does not appear to be a strong zeitgeber because synchronization occurred only intermittently and, during any particular period, the women differed from each other in the courses of their menstrual cycles and in the timing of synodic synchronization."
I'm a little confused by this as I thought this was the whole point: that the synodic lunar cycle does
appear to be a zeitgeber. Indeed, the paper itself says: "We found that all three lunar cycles—the synodic, the anomalistic, and, to a lesser degree, the tropical month—affect menses onset. Nocturnal moonlight appears to be the strongest zeitgeber through which the Moon exerts its influence, but the gravitational forces of the Moon clearly contribute."
Perhaps the key to understanding is in the use of the word "strong" - and this is where the proposed effect of the Saros #137 eclipses is added in: "The conjunction of these two events [full/new moon and Saros #137 eclipse] may have augmented the Moon’s strength as a zeitgeber."
2. “Our principal results are consistent with the results of earlier studies on menstrual, mood, and sleep-wake cycles, which revealed that humans are sensitive to the Moon’s luminance cycle and even synchronize with it. Earlier studies showed that about 22 to 32% of reproductive age women experienced menstrual cycles with 29.5-day cycle lengths and onsets of menses around the time of the full moon.”
Primarily citing the debunked Cutler study here, which simultaneously renders the paragraph irrelevant; makes me sceptical of the quality of the other “earlier studies” cited; and further damages the credibility of the paper as a whole.
3. "While [earlier] studies found onsets of women’s menses that occurred around the time of the full moon consistent with the hypothesis that ovulation happened predominantly at the new moon, we found that onsets of menses also occurred around the time of new moon. Thus, something may have changed over the decades that followed earlier studies.”
That’s a staggering hypothesis to propose, and again incredibly damaging to credibility. Couldn’t it simply be that the earlier studies were bunk? Which is very clearly the case. No need to think that "something may have changed" since the early-1980s that would affect women's menstrual cycles.
4. "We show here that menstrual cycles were intermittently synchronous with the luminescence and/or gravimetric cycles of the Moon, strongly suggesting that both cycles influence reproduction in humans. On its own, each type of lunar cycle appears to be a weak zeitgeber. However, both appear to cooperate, leading to the best synchrony between lunar and menstrual rhythms when the Moon was close to Earth."
Again, if that's the case - that the intermittent synchronicity has been shown - I'm not really seeing it. Maybe someone else can point out the places in the charts where the combination of the luminescence and gravimetric cycles has been shown to affect the onset of menstrual cycles. Mainly, it just seems that they included the data for Subject 5:
This shows some quite prolonged periods of aligning with the gravimetric cycle, and some prolonged periods that didn't. Presumably this was the best example of the 22, since it was the main one featured; and of the other 5 that were included in these charts, the correlation seemed quite weak:
In conclusion, that's my first cursory glance over the paper. The patterns generated by 6 of the women's records - and, to a lesser extent, possibly another 5 (therefore up to 50% of the sample size) - are quite striking and intriguing: it seems that if random chance were the explanation we ought to be seeing more of those "vertical black lines" at different times of the lunar cycle, and I think the probability of only
finding those lines, across multiple subjects, on either full or new moon is pretty slim. So there may be something in it after all. But with so few records to look at, it's impossible to draw any conclusions, other than to say: gee, it would be interesting to look at the data of, say, a few hundred women and see if more patterns like this emerge.
If anything's been "shown", though, I can't see it. And the use of bad previous studies - while ignoring good ones - doesn't bode well for the credibility of the potential conclusions.
Anyway, maybe someone can fine tune, correct, build on, and explain the above. I'm a little bit lost with it right now, after a half-decent start. Probably something to do with the moon...