You know you're supposed to get seven to nine hours of sleep a night, but sometimes, you stay up for a night out on the town, to finish a project at work, or even just to watch Law & Order reruns. We get it—we've all been there, and a late night here and there won't have any lasting effects beyond the fatigue you feel the next day. It's when you skimp on sleep night after night that it becomes a real problem. Though you may think your five-hours-a-night habit is nothing to worry about, chronic sleep deprivation has been tied to an increased risk of type 2 diabetes, cardiovascular disease, obesity, and depression. Read on for subtle signs your body needs more time in bed.
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You're always hungry
"If the brain is not getting the energy it needs from sleep it will often try to get it from food," says Chris Winter, MD, owner of Charlottesville Neurology and Sleep Medicine in Virginia. Running low on rest can increase the production of ghrelin, also known as the hunger hormone, in your gut. Too much ghrelin makes your body crave fatty and sugary foods, Dr. Winter says. Poor sleep can also mess with leptin, the satiety hormone. "When you're not sleeping properly you tend to eat more of what you're craving because you're not feeling the signals to stop eating," Dr. Winter says.
With an increased appetite comes another unpleasant symptom of sleep deprivation: weight gain. "When you're tired, you don't watch what you're eating," Dr. Winter says. "You just look for all kinds of things to help you feel more awake." With ghrelin and leptin already out of whack, your body will crave fried foods and sweets to get you through the day—a surefire way to widen your waistline. A lack of sleep can also have direct effects on your metabolism, Dr. Winter says; it tends to slow down without proper rest. What's more, a 2012 study in the Annals of Internal Medicine found that just four and a half hours of sleep for four days straight can reduce your fat cells' ability to , the hormone responsible for regulating energy, by 30%.
People tend to act without thinking when they're exhausted, says Gail Saltz, MD, Health's contributing psychology editor. "Your ability to say, 'No, I shouldn't have another candy bar' becomes more difficult." This doesn't just apply to pigging out. You also might find yourself doing or saying things you don't necessarily mean, like lashing out at a spouse or ranting at a co-worker. "The main thing is you're less inhibited," says Kelly Baron, PhD, an assistant professor of neurology at Northwestern University in Chicago.
Can't remember what movie you saw last weekend or where you put your car keys—again? Before you panic about having a serious memory problem, know that your brain is probably fine. "When you're tired, you're usually not paying a whole lot of attention to what's going on when trying to make a memory," Dr. Winter says. Still, getting decent sleep is crucial for brain health in the long term. Research from the National Institutes of Health showed that in mice, from the brain. So not getting enough regularly could impair your brain's ability to keep the nervous system clear, Dr. Winter says.
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You're having trouble making decisions
If you've been finding it harder than usual to manage projects at work and home, lack of sleep could be the culprit. "Sleep deprivation can affect speed and higher-level cognitive processing," Baron says. That means essential functions, like problem solving or time management, become even more difficult to carry out. Take this 2009 study in Sleep: researchers asked both sleep-deprived and well-rested volunteers to perform a set of tasks that two times. Between testing, the accuracy of those without quality sleep went down by 2.4%, while the rested group improved accuracy by 4.3%. All in all, poor sleep simply hinders your ability to react quickly.
Yes, tripping over a step might make you a klutz. But do it a few times in a day and it might just mean you're too tired to really focus on where you're going. "When you're tired, there's a lapse in how you neurologically function in general," Dr. Winter says. With lowered reaction time and concentration also comes more difficulty with movement. "When you walk up and down the stairs, there's a lot of processing going on there," Dr. Winter says. "When sleep deprived you can't process particularly well."
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Your emotions are all over the place
You might feel like your emotions are out of control when you're sleep deprived. "You become over-reactive to emotional stimuli," Baron says. So things that normally haven't gotten you worked up in the past—a tear-jerking movie or big work deadline—may provoke anxiety, sadness, or anger. (It could also go the opposite way: "People can get slap-happy and giddy as well," Baron says.)
Another thing that can suffer with poor sleep is your immune system. "If you're not sleeping properly there can be significant issues in terms of your body's ability to fight off infections," Dr. Winter says. In particular, you might find that it's harder to shake off a cold. A 2009 study in the Archives of Internal Medicine followed the sleeping habits of 153 volunteers for 14 days straight. Researchers found that people who got less than seven hours of sleep were nearly three times as likely to than those who got eight hours or more rest a night. That could be because your immune system produces while you sleep, which are proteins that help protect against infections and inflammation, meaning a few nights of poor sleep could lower your body's defenses against pesky viruses.
"When fatigued, you're not able to control the muscles of the eye as well," says Steven Shanbom, MD, an ophthalmologist in Berkley, Mich. First, skimping on shuteye tires out the ciliary muscle, which helps your eyes focus. The result: you'll have a harder time reading up close, Dr. Shanbom says. Then there's the extra ocular muscle, which moves the eye from side to side and up and down. "Many people have a muscle imbalance where their eyes don't track well together," Dr. Shanbom says, but in a well-rested person the eyes can compensate on their own. A lack of sleep makes the misalignment harder to control, potentially resulting in double vision. You might notice both of these vision problems after one night of poor sleep, but they will persist the less time you spend in bed.
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Your skin isn't looking good
They call it "beauty sleep" for a reason. While you're out, your skin works to repair any damaged cells, so not getting enough rest can disrupt the process. A 2013 clinical trial conducted at University Hospitals Case Medical Center in Cleveland, Ohio, found that was 30% higher in those who had good quality sleep over those with poor sleep. "A lack of sleep upsets your hormonal balance and elevates circulating estrogen levels," says Debra Jaliman, MD, a New York City-based dermatologist and author of Skin Rules ($23; ). Not only can you expect more breakouts when you skip out on rest, your skin may also appear older. "If done for long periods, you will see that you have excess wrinkling probably from a decrease in collagen," Dr. Jaliman says. "The body produces it while you're sleeping."
When you nod off for a few seconds without even knowing, it's called micro-sleep. "The brain says, 'I don't care what you want to do. We are going to sleep,'" Dr. Winter says. It's your body's way of forcing you to get the rest you need. The big problem is that micro-sleep can be extremely dangerous if you happen to be driving. Between 2005 and 2009, the National Highway Traffic Safety Administration estimates that 2.2% to 2.6% of total fatal crashes involved . If you ever feel overly sleepy on the road, a safer bet would be to pull over and rest until you feel up to taking the wheel again.