Many people don’t get as much sleep as they should. Since the invention of the light bulb，people sleep about 500 hours per year less than they used to. Whether we，re kept awake by our partner's snoring or we stay up too late watching TV, we wake up tired, groggy, and cranky. No wonder the coffee industry does so well. Unfortunately, sleep deprivation has some side effects and they can’t all be remedied with a little extra caffeine.

Sleep deprivation doesn’t just cause mental deficits; our physical abilities are diminished too. Studies have demonstrated that not sleeping can reduce glucose metabolism by as much as 40 percent. We use stored glucose for energy and sleep deprivation can interfere with how the body stores and processes it Sleep-deprived athletes also experience high levels of cortisol, a stress hormone, as well as lower levels of human growth hormone, which is important for muscle repair. The Immune system is also thought to be maintained while asleep; people who don’t get enough sleep tend to be more susceptible to infections and have slower healing times.

Some of the effects of short-term sleep deprivation can be very similar to the effects of being drunk. In 2000, researchers in New Zealand and Australia found that people who drive after being awake for seventeen to nineteen hours performed worse on tests than people with a blood alcohol level of 0.05 percent, almost the legal limit fox drunk driving. In fact, the US Department of Transportation reports that as many as 100,000 sleep-related auto accidents occur every year.

It’s easy to erase the short-term effects of sleep deprivation-get more sleep. However, when people don’t sleep well for weeks, months, or even years, it can have cumulative effects on their health. Sleep has been shown to be important in regulating blood sugar levels and people who don’t sleep can become increasingly resistant to insulin. Long-term insulin resistance puts extra burdens on the pancreas to produce more, and eventually can result in type 2 diabetes.

Recent studies have also linked chronic sleep deprivation to obesity. Sleep has an important effect on the hormones ghrelin and leptin, which control hunger and appetite. When we don’t sleep, these hormones can go out of balance, causing us to eat more than we need. Heart disease, high blood pressure, and depression are other diseases that can result from long-term sleep deprivation.

It’s common to feel a bit tired in the morning, but how do you know if you're truly sleep-deprived? Sleep experts say that if you feel groggy or tired during the day, feel the urge to nap, or if you fall asleep within five minutes of lying down, you could possibly be sleep-deprived. Another symptom of severe sleep debt is the occurrence of “microsleeps”，short bursts of sleep that can happen without a person even realizing it.

Although most people think they need to sleep for eight hours a night, the amount actually varies from person to person; some are fine with five, others would do better with ten. If you feel like you need more sleep, simple lifestyle changes can help you get more. Missing a few hours of sleep on occasion isn’t the end of the world, because it’s easy to make up the sleep with no lasting side effects. Many people are psychologically adjusted to constantly feeling tired, and in the short-term, their bodies may be able to adjust too. But the long-term consequences of sleep deprivation should be enough to convince anyone to hit the sack.