By Jonny Lupsha, Freelance News Writer

Sleep deprivation research is revealing new side effects associated with a lack of sleep, NPR reported recently. Getting a good night’s rest refuels and resets the brain for the long day to follow. Catch up on why we catch up on Z’s.

The peer-reviewed journal Sleep published a study this year that suggested the quality and quantity of sleep experienced by parents doesn’t fully recover to doctors’ recommendations until six years after childbirth. The NPR article also said that the occasional shortened night of sleep appears to have no long-term effects on us. However, consistently sleeping less than we should can cause sudden weight gain and a drop in insulin sensitivity severe enough to qualify as pre-diabetic. So what does a full night’s rest do for us that’s so important and why do we suffer without it?

Four Theories of Why We Sleep

There are four different hypotheses about the primary functions of sleep—which is surprising since we’ve been doing it every night since time immemorial. The first is that sleep is for restoring our bodies and recovering them after a lengthy period of being awake. Second, sleep helps us consolidate memory and to forget the unnecessary. The third theory is that sleep is significant because of the energy we conserve while sleeping. Finally, the fourth theory around sleep involves a biological history of avoiding predators.

Unfortunately, there is little scientific data that can absolutely prove the third and fourth hypotheses listed about the function of sleeping. While studies show that our metabolism dives while we sleep, scientists have yet to prove the importance of that function. Likewise, some experiments have demonstrated interesting effects of variations in sleep patterns on prey animals and their behavior, but the usefulness of sleep as a means of avoiding predators eludes us. The reason for getting proper amounts of sleep primarily seems to be as an energy restorative.

Sleep as Energy Restoration

The brain needs glucose, which comes from blood, as a constant source of energy. However, all systems of the body hold energy reserves, such as stored fat and carbohydrates, just in case. “The brain has an energy reserve in the form of glycogen, a polymer of glucose,” said Dr. H. Craig Heller, the Lorry I. Lokey/Business Wire Professor of Biological Sciences and Human Biology at Stanford University. “This glycogen reserve is in the glial cells, which synthesize glycogen when there is an abundant source of glucose in the blood.” As the body’s glucose levels fall, the glial cells break down glycogen into more glucose to supply the brain with energy.

Where does sleep come in? “The story is that during wake the glia are poised to give up their glycogen at a moment’s notice if energy levels start to fall,” Dr. Heller said. “During sleep, the glia are put into the mode of replacing their glycogen stores.” For these purposes, glycogen is similar to the gas that fuels a car. During the day, our brains are fueled by glycogen, and at night while we sleep, our body makes more gas for the next day’s worth of brain work. Regularly monitoring glycogen levels is no easy task, but many sleep studies support this as the leading theory.

Getting a good night’s rest seems like a no-brainer, but recent sleep studies show the consequences of sleep deprivation in new ways. Should they corroborate the glycogen theory of the purpose of sleep, scientists may be closer to understanding the biochemical workings of sleeping.

Dr. H. Craig Heller contributed to this article. Dr. Heller is the Lorry I. Lokey/Business Wire Professor of Biological Sciences and Human Biology at Stanford University. He earned his Ph.D. in Biology from Yale University.