I have read in a few different books about the benefits of sleep, and sleeping in the dark, particularly.
I read Lights Out by T.S. Wiley, and I want to try to summarize what I learned by reading it. This next portion is about the importance of sleep.
Here's what it says on the back of the book:
Could keeping the lights on cost you your life? The scientific evidence that obesity, cancer, diabetes, heart disease, and depression are caused by sleep loss - and that your salvation is as easy as the flick of a switch.
The author, through extensive research (the last half of the book is the research cited), maintains that humans beings were designed to flow along with nature and the seasons. That meant eating larger amounts of carbohydrates in summer, putting on weight and having higher cholesterol during that time, mating, and sleeping shorter hours because it was light longer in the summer. Due to the longer periods of sunlight, the hormones in the body are stimulated to encourage us to eat, in preparation for the long winter ahead, when carbohydrates will not be available, and the diet will consist mainly of protein and fat.
Starting in autumn and extending into winter, the shorter periods of sunlight stimulate those same hormones to "shut down" the craving for carbohydrates. The winter is spent in increasing darkness, and primitive people, not having electricity, or even fire in the beginning, would have slept when it was dark. And of course, it was dark for up to fourteen hours per day, as opposed to the summer darkness of nine or ten hours.
During these short days, the fat accumulated during the summer "carbohydrate feast" would begin to be used as fuel, weight would decrease, cholesterol would naturally go down, and in the spring, babies were born to coincide with the availablilty of more plentiful food and the whole cycle began again.
Behind the scenes in all of this was the proper functioning of the major and minor hormones - adrenals, insulin, thyroid and cortisol being among the majors and estrogen, progesterone and testosterone being among the minors.
In the "olden days", when it started to get dark, hormomes would begin go into their natural dance, increasing and decreasing to prepare the body for restorative sleep. One of the crucial things that happened during sleep was the decrease of cortisol, the stress hormone, or the "belly fat" hormone. Without the nightly decrease of cortisol, it would continue, in it's elevated state, to encourage carbohydrate loading and fat storage. Our ancestors stopped craving carbohydrates, even in summer, when it got dark. The very presence of light in the summer was a trigger to eat carbohydrates and store fat in preparation for the long winter months ahead.
Have you ever noticed how you seem to do better "controlling your appetite" during the day than in the evening? So many people say that they just crave snacks, specifically carbohydrate-laden ones, in the late evening, while they are watching television. Could it be that, by extending the normal hours of sunlight to, well, all night, you are unwittingly giving your hormones the signal that it is endless summer, and it's time to carbo load?
Now, the author does not suggest that, in order to be healthy, we should ditch electricity and go live in caves! But there are some lessons that can be learned by how our distant ancestors lived. So what does she suggest?
The answer is to eat and sleep and reproduce in sync with the spin of the planet or go the way of the dinosaurs. The long hours of artificial light that confuses your ancient energy regulation system also destroy the lining of your heart, so excess cholesterol can obstruct blood flow. Your subcounscious has, over the course of evolution, been conditioned and fine-tuned to believe and act on the following when the lights stay on too long: "Eat carbohydrates now or die later." This light-responsive instict has been the basis of our feast-or-famine metabolism and ultimate survival for at least 3 million years. All the effect of chronic light exposure and the carbohydrate consumption that follows that exposure would have, in another place and time, prepared us for the worst - for no food and for the shorter, darker, colder days of less sun.
Think of it this way: Long hours of artificial light equals summer in your primitive head, the time to prepare for the coming famine of winter. By not sleeping at least 9 or 9-1/2 hours a night, you are encouraging your body to increase carbohydrate consumption until your body responds to all the insulin by becoming insulin-resistant in muscle tissue. By doing this, you are ensuring that the carbohydrates taken in will end up as fat stores.
Once more from the book:
Could it really be the loss of sleep destroying the endocrine clock that controls weight gain? Could how much you sleep really control your appetite?
These things I have related from the book are only part of the part of the big picture of how sleep regulates weight. There's more.
Just as an aside, but an important aside, the author of Lights Out believes that Dr. Atkins was right about how human beings should eat. Just thought I'd mention that!