Why does the full moon cause insomnia in some people?

[tacitus81]

Sorry to sign up just to comment on this thread, but it's one of the few that keeps on coming up in searches and I suspect others are also coming across it. Trying to commit as few faux pas as possible.

I've had long enough time series to confirm that something goes wonky around this time of the month. Sleep is disrupted and there are psychological difficulties. There are signs it's genetic - we can trace behavioral instabilities up one branch of the family tree and it's resulted in an en masse diagnosis of really cyclical familial bipolar disorder, not otherwise specified, please don't have kids.

There are signs that our version of bipolar is related to dysregulation of the molecular clocks Pythagorean mentions. For example, when we remember to take it, melatonin has done wonders and not just for sleep. (N.B. Forgot it this time, wasn't paying attention.) We suspect that our version will eventually be diagnosed as a mitochondrial, metabolic disorder, not only because it's followed the women down the line.

http://hmg.oxfordjournals.org/content/14/2/241.short

I'm certainly not saying that everyone who is awake right now has an illness, but we might share bits and pieces of the genes that in less lucky families results in systematic failures of some subsystem. It might be worthwhile to think of it in evolutionary terms - there are obvious advantages for people who find themselves more active when there's more light, less when there's less - but it'd be terribly disruptive if everybody were like this.

If it's actually the case that we're still entrained, I'm much more likely to believe that it's about sensing the moon phase through changes in the environment than a direct interaction with the moon. Plants, for example, contain markers for moon phase:

http://www.bioone.org/doi/abs/10.1579/0044-7447-31.6.485
http://dx.doi.org/10.1017/S0025315400009565 (very old, but interesting as it claims the moonlight is not responsible!)

Bugs do, birds do, fish do, etc. I would not be surprised if microorganisms do. So perhaps the moon is ultimately to blame, but organisms were sensing it a thousand million years before we got to the scene. We wouldn't have to reinvent the wheel by sensing the moon phase directly - we'd probably be led in that direction by food sources that entrained us. If we are looking for a way to sense the moon phase, there are so many markers on the ground.

I'm not saying physics has no say here - light is a zeitgeber - but the answer is probably in evolutionary biology.

 

[Pythagorean]

I have suffered with sleeplessness during Full moon period for a few years. The light may be of some significance but there is very little attention given to the gravitational pull at full moon phases. I find it curious that if the moon controls tides and female cycle that there would be doubts about other effects on our bodies. It would be useful if a scientific programme was started with sleep studies to work out who suffers and why. For me, this last August moon was 5 days of no sleep. the most intense period ever. It could be because I am in menopause. Whatever happens, its affecting melatonin levels in my body and makes me feel wide awake. Be great to talk to a physicist about this?

There is no evidence of the moon's effect on menstrual cycle.

Tides are explainable. The moon causes tides because of the differential of force from one side of the planet to the other. The moon's total force is actually much much smaller than the sun's. Humans are essentually just a point particle compared to the Earth, so the differential effect does not affect us.