Question of the Week

Does the moon cycle affect human physiology?

Mon, 30th Sep 2013

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Martin Taper asked:

I heard you on ABC Breakfast talking of the full moon effect. I have suffered in no small way from it all my life and medicate myself to sleep in a full moon, otherwise I don't sleep. As an engineer and science interested person I have thought a lot about this phenomenon and have come up with a theory, which I'm very surprised has not been considered previously.


You said in your article that gravity was excluded as a factor, but this is not the case. Gravity is affected by the mass of the moon and it's proximity to your location. The tides have complex interactions with the earth and the sun, so making conclusions from the tides alone is not always valid in relation to gravitational forces. Lakes are not tidally affected because there is no where for the water to go. The ocean tidal waters don't go up and down like a bath tub level, they go in and out like the waves on a beach.


I conclude that the increase of the gravitational force makes sensitive people restless, and hence in a sleep lab, they are still exposed to gravitational changes. I suggest the way to verify this is to measure the gravitational force at different cycles of the earth and moon.


I am also affected by air pressure in a similar way.When the air pressure is high, and it'sa full or near full moon, I'm unable to sleep without medication, and if I do partially sleep, I have wild dreams. When the opposite is the case, I sleep like the dead. Temperature is the other obvious variable that exacerbates this cocktail of influences as well.


Also, from a natural selection view, maybe we are restless at times of full moon as we are more visible to night predators, and need to keep more alert for that.


As I said, I'm amazed that science hasn't resolved this question a long time ago. So much of nature is cycled by the moon.



Martin Taper


Hannah - To answer Martin’s sleepless question, we turn to clock doc, John O’Neil The moonfrom the Laboratory of Molecular Biology in Cambridge where he works on circadian rhythms. But what exactly are circadian rhythms and how is it relevant to Martin?

John - Your circadian rhythm is the approximately 24-hour biological clock that ticks away in every cell of your body, priming us for wakefulness in the morning and making us feel sleepy at night.

Hannah - Aha! So, could the moon cycle or atmospheric pressure changes affect our circadian rhythms in some way and disturb sleep. Let’s start with atmospheric pressure. What's the data on that?

John - I'm afraid there is very little that's known about the effects of high atmospheric pressure on human sleep.

Hannah - That's disappointing. Okay, well what about the moon? Is there any data linking the lunar cycle to Martin’s reports of disturbed sleep and wild dreams?

John - When it comes to lunar cycle, beyond the historical folklore, the moon very much continues to influence modern day human cultures. But despite a persistent belief that our mental health and other behaviours are modulated by the phases of the moon, until very recently, there has been no solid evidence that human biology is in any way regulated by the lunar cycle.

It has been speculated however, that just like with the circadian clock which synchronises to the cycle of day and night, there may exist in humans a lunar rhythm that synchronises with the phases of the moon, as has been observed in certain marine organisms. So, just last month, Anna Wirz-Justice and colleagues performed a retrospective analysis of human sleep data, collected under stringently controlled laboratory conditions with neither the participants nor the investigators being aware of the lunar phase. They found that during the full moon, on average, participants experienced a 30% decrease in deep sleep, otherwise known as NREM sleep, a 20-minute reduction in total sleep, and that it took 5 minutes longer to fall asleep even though they didn’t know it was the full moon. This implies that lunar rhythms do exist in humans and it would seem reasonable to expect that some individuals such as your listener perhaps are more sensitive to them.


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The gravitational force of the moon on a person on Earth is less than the weight of a banknote.

The moon exerts the same gravitational force whatever phase it is in : a full-moon does not pull more than say a half-moon. So if there is a full-moon lunar-effect on people it would have to be a visual mechanism , zeitgeber, psychological (analogous to placebo-effect) and confirmation-bias ]. 
RD, Sun, 28th Jul 2013

Martin, cycles of roughly 28 days are certainly not unheard of in humans - ask any woman.  Could it be that your sleep pattern just happens to co-inside with the phases of the moon in that remarkable way? Bill S, Sun, 28th Jul 2013

On the visual effect, could the moon reflect enough sunlight to disturb one's sleep cycle?

          Lunar Radiation Spectrum

Or, sleeplessness during a full moon might be an evolutionary development that diurnal predatory animals (including other humans?) might be on the prowl, so stay alert. Lmnre, Mon, 29th Jul 2013

@RD, if the force between the earth and the moon were less than a bank note, the moon would not be there, as it is the attractive force between the masses that contributes to it's sustained position in orbit around the earth. to suggest that there is no force between these two celestial masses denies established and proven science. tin, Mon, 29th Jul 2013

yes the moon exerts the same gravitational effect on the earth, which you incorrectly state is that less of a bank note, but the moon rotates over 28 days and the earth rotates every 24 hours, hence affects different parts of the earth differently at any one time depending on it's proximity.
tin, Mon, 29th Jul 2013

I didn't say that, I said ...

You can calculate the force yourself ...

m1 is the mass of the moon , m2 is the mass of a person (not the mass of the earth)

Yes the gravitational force of the moon will act in different directions on the person on Earth depending on the alignment , and will vary minutely in strength due to the person-moon distance not being constant.
But nevertheless the force on a person is negligible , less than the weight of a banknote, (some compare the moon's force on a person on earth with the weight of a gnat). RD, Tue, 30th Jul 2013

okay, let's for the moment agree the effect of the moon equates to a bank note under earth's gravity on a person, and that same bank note, which may not even break the surface tension in a bucket of water, manages to influence the ocean water levels on the surface of the earth by metres in height. taking into consideration that a cubic metre of seawater has a mass in excess of 1 metric tonne, i fail to take your point that something like the force of less than 100 bank notes counteracts a tonne of water. the moon influences significantly and affects the size of tides considerably as to it's relative position and proximity to the earth. the same forces act upon everything else on earth as well, and hence the influence on many natural cycles. the approximate force exerted by the moon on the earth is 20,180,000,000,000,000 tonnes as calculated by Newton's Third Law of Motion. Reducing that to the force on an approximate area of a bank note (.01 square metre) on the earth equates to approximately 1.5 tonnes per bank note. I don't know of any bank notes that heavy. tin, Tue, 30th Jul 2013

Oceans are on average several thousand meters deep , (rather than one meter)  ...

So the gravitational force of the moon on a square meter of ocean is, on average, affecting thousands of cubic meters of seawater, so that’s a force equal to the weight of several hundred thousand banknotes, which is more than enough to break the surface tension on a square meter of water

The moon’s gravitational pull on the water does not equal the weight of the water : you do not have to apply a force equal to an object’s weight in order to move it , just sufficient force to overcome friction hydrogen bonding ] is required, e.g. a single person cannot lift a truck off the ground, but they move it by pushing  or pulling it ...  RD, Tue, 30th Jul 2013

The depth of the ocean is irrelevant. The whole ocean is not being lifting by the tide, but it is rising or falling by the height of the tide, often around the 1 metre mark in many locations, and the force required to lift a mass of water is just greater than the force exerted by it’s mass. On the high tide water is pressed from the region where the corresponding low tide is happening. The whole ocean mass is not lifting or falling. As a crude analogy, it is like the bulging of a soft jelly in a bowl being wobbled.

Yes a hundred bank notes in a pile will break the surface tension of water, but they are not in a pile, they are spread over one square metre, as I explained, and in any case, the hundred notes won’t balance a cubic metre of water weighing at over 1 tonne on the end of a weighing scale!

You do have to apply a force just greater than the mass of water if you are to lift the water to a height, such as a tidal force does. One cubic metre requires about 1.024 tonnes to balance. The 24kg being dissolved salts and minerals adding mass. The hundred bank notes or a million gnats just won’t do it.

Tides do not move water from one side of the earth to the other.  Your example of pushing a truck is not the same analogy as lifting a truck. The tides lift the water. An ocean current is more analogous to pushing a truck.

As you suggest the moon has no effect on the tides, so what do you suggest causes them? The sun contributes, but if it were only the sun causing the tides, they would be at the same level each day and each night, but as we know, they are not.

By the way, the metric SI unit of measurement is the metre, not the “meter”.
tin, Wed, 31st Jul 2013

The depth is significant : if the oceans were shallower the extent to which tides rise and fall would be proportionately less.

I never suggested that. I said that the gravitational force of the moon on a single human on earth being is negligible :  it would not affect their physiology. The gravitational pull of the Moon (and the Sun) causes tides in Earth's oceans in Earth itself]. RD, Wed, 31st Jul 2013

Meter is the accepted American English spelling.  Both are acceptable so long as one is consistent. jpetruccelli, Wed, 31st Jul 2013

"meter" might be accepted American spelling, but the French invented the metric system, and they would suggest otherwise to the Americans who are on the whole living with  feet, inches and yards for reasons baffling. a "meter" is also a word with other various meanings where as a "metre" has only one meaning. inviting confusion invites errors, and the Americans have had some great blunders with trying to live with metric and imperial systems. not only do they not go metric, they vary their own size of some imperial units from the English units to make even more confusion. tin, Fri, 2nd Aug 2013

so there is a force great enough to shift the tides but so small that it has no effect on human physiology at all, which is mostly water based - a very unsound proposal. however i'm glad that you now agree that the tides are driven by the moon as that seemed to be in doubt previously. as far as the depth of oceans are concerned, you'll find that the deeper the body of water, the far less it is affected by tides. think about the jelly on a plate again, when you wobble it the top moves a lot, and the base stays still. there are so many other factors in tide height such as proximity and geography of land, ocean floor geography texture and density, water specific gravity, river mouths, coast profiles, ocean water density, currents, weather, and so on. tin, Fri, 2nd Aug 2013

I don't like the imperial system either, but that doesn't make you any more correct in claiming that "meter" isn't an accepted spelling. jpetruccelli, Fri, 2nd Aug 2013

This is a UK based international website and not a USA based national website. It would be fair to suggest that the SI unit international term in the English language of "metre" is preferred and encouraged, and especially as this is a science based site. I take your point that the USA has an alternate accepted spelling in the USA, but elsewhere this spelling is not accepted. It certainly is not accepted in the country of origin where the language is protected by law, and incorrect usage may be legally prosecuted. The SI International System of Units defines the "metre" unit spelled this way in English, and this is the case for most if not all other English speaking nations. tin, Sat, 3rd Aug 2013

You don't have to turn everything into an argument.  It is accepted spelling on this website.  :) jpetruccelli, Sat, 3rd Aug 2013

I have recently left another forum because almost every scientific discussion seems to be channelled into religion, philosophy, politics etc.  I hope TNS will not be allowed to go the same way.

Tin, do you convert to American spelling when posting on American based international sites?  I don’t.

Personally, I think it a complete waste of time to correct linguistic usage, as long as the poster can be understood; that is why I would, normally, not mention that in the above quotes, “alternative” is the correct (UK) English word and in correct English, we start sentences with capital letters, but let's stick with the real discussion.

I can’t agree that “the deeper the body of water, the far less it is affected by tides.” The effects of the tides are more evident as the water becomes shallower, but the deeper water is still influenced.  Your statement about the jelly on a plate is obviously correct, but the deeper the deeper the jelly, the more the upper regions wobble, and greater is the depth at which motion is evident, so your example does not really support your argument.

Surely, that is precisely what tides do.
Bill S, Sat, 3rd Aug 2013

Honestly this seems like a plausible theory to me. Most animals have the ability to interpret magnetic fields, like birds use for migration, and why astronauts have issues in space. Although to my knowledge it isn't fully understood, the pineal gland is thought to be the area of the brain that interprets electromagnetic fields...among other things like controlling our circadian rhythm and melatonin production, which would relate to why you have trouble sleeping during a full moon. Bassphere, Sun, 2nd Feb 2014

I've heard that jogging or similar types of exercises are better at night because the gravitational pull makes you lighter on your feet. Is this true? G.Gonzalez, Tue, 18th Mar 2014

In reply #1 it is said:

"The moon exerts the same gravitational force whatever phase it is in : a full-moon does not pull more than say a half-moon".
That is just half a truth ... You are forgetting Sun´s influence. When full and new moons Sun´s tidal effects are in same direction than Moon´s, and both effects have to be added up. That´s why those days tides are much stronger than when "half moon"! rmolnav, Fri, 29th May 2015

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