If you’ve ever been in a hospital and been treated by a resident instead of a full-fledged doctor, you may have noticed a few things. Your doctor may have looked a bit disheveled, may have been somewhat curt or cranky, or even a bit too happy given the medical circumstances. The doctor may even have had a distinct unpleasant odor. The reason for all this can be summed up in one word: sleep. Or rather, lack of sleep. Residents often work killer shifts of 30 hours or more in a row. The lack of sleep can result in severe health issues for the sleep-deprived; not just hospital residents, but for all of us who don’t get enough shuteye.

In Atlantic editor James Hamblin’s new book, If Our Bodies Could Talk: A Guide to Operating and Maintaining a Human Body, he uncovers some surprising and little-known facts about sleep. Hamblin writes, “Sleep experts often liken sleep-deprived people to drunk drivers: They don’t get behind the wheel thinking they’re probably going to kill someone. But as with drunkenness, one of the first things we lose in sleep deprivation is self-awareness.”

Here are five more things your sleep-deprived body is trying to tell you, according to Hamblin.

1. We need this much sleep.

There have been many studies over the years trying to pinpoint just how many hours of sleep the human body needs for optimum health. One 2014 study in Finland of 3,000 people came up with the number 7.63 hours a night for women and 7.76 hours for men. These were the hours of sleep that resulted in the fewest sick days. As with many isolated studies, however, the conclusions were open to many questions. Were men who slept 7.76 hours really healthier? Or were they just less likely to call in sick than if they had slept 5 hours? Or were underlying illnesses in individuals that had nothing to do with sleep causing them to sleep more or less?

Other studies posed similar questions. The American Academy of Sleep Medicine decided to review all of the known research on sleep and health, particularly the effects of sleep on heart disease, obesity, cancer, cognitive decline, and general human performance. After careful study, their conclusion: humans need between 7 and 9 hours of sleep a night for optimum health. Anything less than 7 hours results in decreased performance, and consistently falling below 6 hours increases the risk of health issues.

2. We can’t train ourselves to need less sleep.

In 1964, a teenage high school-er, as part of his science fair project, decided to stay awake for 264 straight hours. Although he made it through, and with no apparent long-lasting effects, he was lucky. Not sleeping can be a killer. “When animals are sleep-deprived constantly, they will suffer serious biological consequences. Death is one of those consequences,” David Dinges, the head of the sleep and chronobiology division at the University of Pennsylvania told Hamblin.

A practice known as polyphasic sleeping has become popular among a small number of people around the world. The practice involves breaking up the person’s daily sleep into segments, maybe 4 hours of sleep followed by a period of activity followed by an additional 4 hours of sleep, for instance. While this might allow for a sense of a more active waking life, the body still needs the requisite 7-9 hours a day without which even polyphasic sleepers suffered physical and cognitive decline.

Although no amount of training appears to overcome the need for adequate sleep, Dinges notes that a tiny segment of the population are "short sleepers," and can get by on just 4 or 5 hours of sleep without apparent detriment to their cognitive abilities. Even then, though, there is no definitive study to show how short sleeper metabolism or other factors, like mood or hyperactivity, are affected by reduced sleeping time. 

Even mild sleep deprivation can cause a drop in human performance. In a study by the journal Sleep, subjects were allowed only 6 hours of sleep a night. Even though the subjects protested that they felt fine, their performance levels on cognitive tests significantly dropped.

3. Caffeine is no substitute for sleep.

Eighty-five percent of American adults drink caffeinated beverages every day, at the rate of about 27 ounces a day. Caffeine works by increasing the amount of adrenaline in the blood while in turn switching off the neural “relax” switch in the brain. In the short term this can provide real performance boosts, both cognitively and physically. In the long term, however, by bombarding our bodies with a constant caffeine buzz, we are tampering with our internal body clocks and making it more difficult to fall asleep when we want to.

As for reports in the media about the healthful benefits of coffee drinking, studies have found only correlations between coffee drinking and health benefits, not actual proof that coffee causes the health benefits. Studies involving nutrition and health are often misguided due to the countless variables involved in the individual and the many underlying factors going on in human metabolism. Many often point to coffee’s antioxidant content, for instance, as proof of its benefits. However, there is not convincing data to show that antioxidants work as proponents think they do, and in fact there is some convincing data showing that some antioxidants can be harmful, such as the increase in the risk of prostate cancer caused by taking vitamin E supplements.

Meanwhile, there have been alarming increases in the number of emergency room visits related to the ingestion of caffeine-infused energy drinks like Red Bull. Although the visits and the caffeine ingestion may, in many cases, be simple correlations, and perhaps underlying causes like heart defects may be the true problem, over-caffeinating is a problem that bears keeping an eye on. For the most part, most people are not in danger of OD-ing on caffeine, beyond the jitters and sleepless nights.

4. Nighttime electronics disrupt your sleep.

Cell phones, computers and tablets are undeniably the magic of the 21st century. We use electronics with reckless abandon, including at night, when we read books on our tablets or read the newspaper or the latest sports scores on our phones. The problem is that these devices emit a blue light, and this blue light disrupts sleep.

Light enters the eye, which sends a signal to a part of the brain called the hypothalamus. The hypothalamus, among many responsibilities, like controlling heart rate, is in charge of our sleep cycle. When it gets dark, the eye takes in less light, which signals to the hypothalamus that it is time to sleep. It, in turn, tells the nearby pineal gland to produce melatonin, a hormone that makes us sleepy. When daytime rolls around, the hypothalamus senses more light and tells the pineal gland to knock off the melatonin production, and we wake up.

The blue light from our electronics, however, confuses the hypothalamus into thinking it’s daytime, so our melatonin factory shuts down, making it hard for us to fall asleep, even though it may be midnight. Some electronics manufacturers have attempted to minimize this effect by programming a night shift mode, which skews the light their products emit toward the yellow rather than the blue end of the spectrum. The jury is still out on how effective this is.

5. Melatonin supplements are a questionable remedy.

Since blue light affects melatonin production, why not just take a melatonin pill to compensate? Well, it may be worth trying, although the bloodstream generally eliminates the pill form before the end of the night. Some people are able to fall asleep more quickly with the melatonin supplement, but there is no real proof that it improves the quality or quantity of sleep you get. Not only that, but because of the nature of how the supplement industry is regulated in America, there is no guarantee that your supplement contains what it says it contains.

The long-term effects of these supplements are unknown. Hormones like melatonin tinker with the body’s functioning, and David Dinges warns, “No child should have a melatonin supplement—or a caffeinated drink—without a doctor being involved.”

So we know we need a certain amount of sleep. We can’t train ourselves to sleep less, caffeine presents issues, as do our electronics, and melatonin is an uncertain and problematic solution. What to do? Experts recommend a number of fairly simple solutions:

  • Go to bed at the same time every night when possible
  • Wake up at the same time every day if possible
  • Keep your caffeine intake at a moderate level, and resist it at night
  • Keep your alcohol intake at a moderate level
  • Put down your electronics at night
  • Substitute a book, magazine or newspaper instead, or even better, have sex