So far, I don't know of any research to suggest that there are important effects related to the transition from night to day and vice versa. There is some research to suggest that before electricity, when you could easily see 12 hours of darkness, people would go to sleep at sunset (nothing else to do), wake up in the middle of the night, lie there and talk quietly (still in darkness), then fall back asleep.
It's worth noting that the melatonin cycle and sleep are related but not identical. If you wake up in the night but keep light from getting to your eyes, the act of waking up does not shut down the melatonin cycle as far as I can see from existing research. But if you get up 2 hours early and turn on the lights, you will both send a signal to shut down pineal melatonin, and also nudge the 24-hour clock to try to start the melatonin cycle earlier the next day (loads of detailed research into clock-nudging, due to desire to extract maximal labor from night/swing shift workers!).
I know it sounds hypocritical or something but I would rather stay in ignorance!
Being 100% rational is not the best way to get through life. Rationality is good for choosing medicines, not so good for choosing sofas and life partners.
And I have an apple maybe every few days, thats it for the fruit, so I think there is very little fructose in my diet. I do want to be able to eat these things in moderation again at some point, so does that mean if I do I just have to eat them only when my gut fully knows that it is daytime and after my savory meals? oh yeah, what time do you eat dinner?
My (current) hypothesis says that I can eat just about anything when I'm spending all day outdoors in bright light. Exceptions are: caffeine, (possibly) dairy, and there's always some large-enough amount of fructose that can hurt anybody (though I claim living in bright light raises the amount you can process). I try to eat dinner (aka "supper" in some parts!) several hours before bedtime. There was a recent mouse study that showed mice put on way more fat when fed more calories during their normal sleep period. It will be interesting to see if that turns out to be a side-effect of the fact that the intestines are on the same 24-hour light-controlled clock as other parts of the body.
I've been thinking about this a lot, and it confused me that there are some people I know who spend way more time in dim light during the day, even sleep in the day and are up all night and eat crap, and have no acne.
The "why us" question is really hard, given that we're still waiting for someone to prove that any of the many different theories of how acne actually works is the right one. There is existing data to show that the ability of light in the eyes to suppress melatonin can vary greatly from one person to another (almost every study -- and these are usually small studies -- shows at least one freak who is a total outlier if you look through the details of the dataset). One study claims brown eyes have more difficulty suppressing daytime melatonin. But if it were fairly easy to distinguish who gets acne from who doesn't, that would have been a giant clue and research would be further along by now.
Could drugs affect your melatonin cycle? Sure, but less obvious is how they would produce long-term changes. The relationship of the menstrual cycle to melatonin/acne has more interesting facts. It's a fact in rats at least that estrogen helps suppress pineal melatonin. My hypothesis says that's probably true in humans as well, and therefore explains both monthly "hormonal acne" in menstruating women and "menopausal acne", when estrogen levels go on a permanent significant decline, making it harder for artificial light to have enough intensity to effectively suppress daytime melatonin. (Menopausal acne is interesting because it tends to "go away" much like adolescent acne, posing the question whether there's some mechanism for adapting to an impaired melatonin cycle that chronic acne sufferers lack.)
I've had my hormones tested and the results were normal, melatonin is a hormone right? But not a sex hormone so I don't think I would have been tested for it.
The definition of "hormone" is in the eye of the beholder. Essentially, any chemical one cell emits that travels to some other cells and tells them to do something is a "hormone". So there are innumerable "hormones" in the body, most completely unrelated to sex organs (Vitamin D3 is a hormone). Because melatonin is strongly cyclical, it makes no sense to measure it, unless you measure it periodically through an entire day's cycle. That's why I say you can't measure melatonin without checking into a sleep lab, where they hook you up to something to sample blood or urine periodically.
And another point I was gonna ask you about was in reference to even the slightest bit of light can destroy your night time melatonin surge. What about moon and star light? Surely the neo-Paleolithics had this in their environment, so why can't we?
First, our eyes ability to detect light is non-linear, meaning that even though we might think a sky full of stars looks as bright as the LEDs on the alarm clock next to our bed, they really aren't. Like all radiation, light is an inverse square law phenomenon. The intensity drops with the square of the distance (double the distance, you get one-fourth the intensity). The stars are a really long ways away. Your alarm clock LED is very, very close to your head compared to the moon or stars and needs way less energy to affect your eyes.
Second, the moon probably is bright enough to have an effect on human pineal melatonin (and has been proved to have an effect on various fish). I know of no human study to try to measure the degree of suppression moonlight can have. In the meantime, I'll assume it's not highly effective at suppressing melatonin (doesn't have to be highly effective to offer a big enough signal to influence things). It is even suggested that the moon may have gravitational effects
on our physiology, but that sounds to me like the speculation of a biologist who doesn't actually understand how insanely tiny the gravitational differential of the moon is within the space of one 6-foot human.
It's also interesting to note that humans don't seem to like to sleep exposed to moonlight. (well, probably we just don't like being rained on) Certainly the acne-free Trobriand Islanders that Cordain studied sleep in huts. Probably not 100% effective at eliminating moonlight, but probably greatly reducing the amount that reaches the eyes.
But in the big picture, it seems to me that even if acne-free tribes slept with their eyes open looking at the moon, the stark comparison of that light signal with being outdoors (often in bright sunlight) all day everyday just gives their body's system clock a much better defined signal of day versus night than most of us get. Combine that with: no easy daily access to caffeine (AFAICT), no easy daily access to high-fructose fruits or sodas (AFAICT), no dairy, regular exercise (exercise helps get tryptophan into the brain where it can be used to make melatonin), low glycemic load diet, lots of Vitamin D the natural way -- then even while admitting nobody knows exactly how acne works, you can sure see a whole lot of factors in favor of making their entire island of people free of acne. They've got a bunch of possible exacerbators covered.
From this panoply of factors, Cordain focuses on low glycemic load and dairy, which I think is probably what he went into it looking for (I'm guessing the effects of light and melatonin never occurred to him). He may be right, but I doubt he's more than partially right. He now sells acne cure courses on the side, but hasn't produced a single study showing some better-than-usual results that could come anywhere close to being a "cure" (though the word "cure" appears a lot in his marketing literature). He also eventually started saying more or less "and, um, you might need to take a zinc pill". I infer from that that his diet probably produces the usual mixed results of most attempts to treat acne via diet, so he's then left to fumble for whatever else can be thrown against the wall to see what sticks. Maybe I'm wrong and he's got a stunner of a diet study just around the corner... but he has had a few years to get that together. I fear he's found what so many have before: curing acne is damn tough (probably because there's something crucial we don't understand), but there's good money in selling anything that offers just marginal improvements.
Edited by databased, 04 September 2009 - 12:15 PM.