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What's the connection between the human menstrual cycle and the moon? Do cycles last exactly one lunar month for a reason, or is it just a coincidence?

It looks like it's coincidence. In Science and the Paranormal (1983), astronomer George O. Abell writes, "The moon's cycle of phases is 29.53 days, while the human female menstrual cycle averages 28 days (although it varies among women and from time to time with individual women); this is hardly even a good coincidence! 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. One could argue, I suppose, that the human female, being more intelligent and perhaps aware of her environment, adapted to a cycle close to that of the moon, while lower animals did not. But then the 28-day period for the opossum must be a coincidence, and if it is a coincidence for opossums, why not for humans?"

Then again, who knows? People have figured there was a connection between the lunar month and menstruation for as long as women have been getting the monthlies. Moon, month, and menstruation are all related etymologically. No less an authority than Charles Darwin believed that menstruation was linked to the moon's influence on tidal rhythms, a legacy of our origin in the sea. The coincidence between the lunar and menstrual cycles is closer than George Abell would have us believe--studies have found the average menstrual period is 29 days and change. At least some critters' biologies are linked to the lunar cycle; in the lemur, for example, estrus and sex tend to occur around the time of the full moon.

Efforts to turn up similar patterns in humans have had unimpressive results, however. Several researchers over the years have claimed to detect lunar rhythms in menstrual onset and such; others see nothing. Biologist Winnifred Cutler, in a 1980 paper, found that 40 percent of women in a random sample showed "a preponderance of menses onsets in the light half-cycle of the month" (the two weeks centered on the full moon). To me this suggests 60 percent of the women didn't show any coincidence. If there really is a moon-menstruation link, it hasn't been convincingly proven yet.

Date: 2002-02-01 07:11 am (UTC)
From: [identity profile] rgladiator.livejournal.com
Don't forget that the pill can re-time the cycle. Also, the moon is moving away from the earth (about a few inches every 100 years or so), while this isn't much, over thousands and millions of years it will alter the moon cycle. Finally, it often happens that women who live closely together will tend to synchronize their cycles for as yet unproven reasons.

Re:

Date: 2002-02-01 07:22 am (UTC)
From: [identity profile] scottobear.livejournal.com
Absolutely correct! if you want to go to a macro scale, that's about 24 miles every million years.

as for synched mensing, the prevailing theory is pheromones. - http://www-news.uchicago.edu/releases/98/980311.McClintock.shtml
(deleted comment)

Re:

Date: 2002-02-01 08:30 am (UTC)
From: [identity profile] rgladiator.livejournal.com
Good proof, but they still haven't fully proven it yet. My vote is for the pheromone theory though.

Re:

Date: 2002-02-01 08:33 am (UTC)
From: [identity profile] scottobear.livejournal.com
I tend to agree!

Re:

Date: 2002-02-01 08:39 am (UTC)
From: [identity profile] scottobear.livejournal.com
I tend to agree! that's been followed up with numbers, anyhow.

Re:

Date: 2002-02-01 09:02 am (UTC)
From: [identity profile] scottobear.livejournal.com
yup... the link mentioned in there has some studies that confirm it.

Date: 2002-02-01 09:24 am (UTC)
From: [identity profile] lunalyn.livejournal.com
II’ve seen this happen. While I was still menstruating, I regulated the "flow" in the house (Me and three daughters). When I had a hysterectomy last spring, my two daughters that were still living at home both missed and entire period!

Date: 2002-02-01 08:11 am (UTC)
From: [identity profile] cath555.livejournal.com
hmmmmm..... never really bought into it myself. especially since I've been bucking nature and enjoying predictability through chemicals for a while.

for your next instalment, maybe the connection between the moon and insanity (lunacy)? that I've always wondred about :-)

Re:

Date: 2002-02-01 09:03 am (UTC)
From: [identity profile] scottobear.livejournal.com
mostly folklore...but some folks get weirder, surely.

Date: 2002-02-01 08:25 am (UTC)
From: [identity profile] eebomb.livejournal.com
Very enlightening.
I still feel that there is deeper symbolic lunar connection, with the waxing and the waning and such.
Hmmmmmm. I will think about this a bit.

Re:

Date: 2002-02-01 09:01 am (UTC)
From: [identity profile] scottobear.livejournal.com
I feel that there's a powerful mythology, but the facts don't seem to match... a shame because I enjoy finding synchronicity.

Date: 2002-02-01 09:37 am (UTC)
From: [identity profile] lunalyn.livejournal.com
My theory of this is: If you don't put yourself in touch with "lunar vibes" you aren't regulated by them.
In Inga Muscio's book “Cunt : A Declaration of Independence" (http://www.amazon.com/exec/obidos/ASIN/1580050158/qid=1012584590/sr=2-1/ref=sr_2_11_1/102-6310692-4895364) she discusses how you can regulate your periods to coincide with lunar movement.

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