We all know that missing sleep doesn't feel good. It makes you less able to think clearly, focus well and makes most people feel more moody (in other words, grumpy). But a lack of sleep can do more than that. It can add an inch to your waistline, and it could also cause a little bit of damage to your brain.

Dreaming of a thinner waist

Published in the journal PLOS One, a U.K. study from the University of Leeds found that those who averaged six hours or so of sleep a night had about one inch more on their waistlines than those who were able to average about nine hours a night.

The 1,615 adults who participated in the study reported on things like how long they slept and what foods they ate while researchers collected blood samples for cholesterol and sugar levels and gathered measurements on blood pressure, weight and waist size over the course of the short study. How long they slept was compared to the other measurements.

In addition to thicker waistlines, researchers found that those who didn't count enough sheep also had reduced levels of HDL cholesterol, the "good" kind of cholesterol that removes "bad" from the body. This, in turn, helps to guard against various conditions, such as heart disease. Somewhat surprisingly, less sleep didn't align with a less healthy diet. Previous research had indicated a lack of sleep often resulted in bad eating choices.

Still, the findings from the study support the ever-growing evidence that sleep has an impact on the health, including obesity.

This is your brain without sleep

And it's not just your waist that's in trouble if you don't get enough sleep. A 2014 study, published in the journal Sleep, says that pulling an all-nighter or regularly sleeping less than you should can actually damage your brain.

The study's researchers looked at specific proteins that are usually found in brain-injured people (concussions) and found that those protein levels were higher (20 percent higher) in people who worked all night, compared to a control group that got a good night's rest. While the levels weren't as high as the protein levels found in concussed people, the study shows that lack of sleep does real physical damage to the brain.

"It's during sleep that unimportant synapses are discarded and the important synaptic ties are strengthened," Emerson Wickwire, Sleep Medicine program director at Howard County Center for Lung and Sleep Medicine in Columbia, Maryland, and assistant professor at Johns Hopkins School of Medicine, told Fast Company. Wickwire was not involved in the study.

When you lose sleep (or worse, don't sleep at all), you brain is unable to do those important repairs and maintenance activities. Outside of it affecting your brain, the work you do while sleep-deprived is also likely to be riddled with errors. Think you are better than that? Many of the most significant disasters of the last 20 years are due to lack of sleep and ensuing human error, including the Challenger disaster, the Chernobyl explosion, the Exxon Valdez Oil spill and plenty of others (and near-misses) — and these were mistakes made by highly trained, experienced professionals. Who needed more rest than they got.

How sleep deprivation disrupts brain activity

woman with insomnia lying awake in bed Being awake when you should be sleeping affects your mental performance. (Photo: Marcos Mesa Sam Wordle/Shutterstock)

A small study in 2017 looked at the cause of those sleep loss-induced mental lapses. Researchers found that sleep deprivation disrupts brain cells' ability to communicate with each other. The researchers believe that disruption leads to temporary mental lapses that affect memory and visual perception.

For the study, researchers studied 12 patients with epilepsy, who had electrodes implanted in their brains for surgery. They were staying up all night because a lack of sleep can trigger epileptic attacks. While they were up, researchers had them sort images as quickly as they could. The task grew more challenging as the patients grew sleepier.

“We were fascinated to observe how sleep deprivation dampened brain cell activity,” said lead author Yuval Nir of Tel Aviv University in a statement. “Unlike the usual rapid reaction, the neurons responded slowly and fired more weakly, and their transmissions dragged on longer than usual.”

The study was published in the journal Nature Medicine.

For the record, you can't make up for the damage done by missed sleep once it's behind you. But you can minimize damage by banking sleep (that is, sleeping more in advance of a time you know you're going to sleep less).

It can also drive away your loved ones

A lonely woman on a swingset Sleep deprivation can affect your mood and lead to loneliness and social isolation. (Photo: Antonio Guillem/Shutterstock)

We've all had those days when we didn't get enough sleep and felt grumpy all day long — and those around us noticed.

According to a study from the University of California, losing sleep can affect your relationship with others.

"The less sleep you get, the less you want to socially interact. In turn, other people perceive you as more socially repulsive, further increasing the grave social-isolation impact of sleep loss," study senior author Matthew Walker, a UC Berkeley professor of psychology and neuroscience, told Medical Xpress. "We humans are a social species. Yet sleep deprivation can turn us into social lepers."

The study surveyed 18 college students on nights they got a normal amount of sleep and nights when they didn't. Researchers found that students who were sleep deprived stayed between 18 and 60 percent further away from other people compared to students who had a full night's rest. The researchers also analyzed brain scans and found that sleep deprivation increases brain activity in a neural circuit known as the "near space network," where the brain perceives potential incoming human threats. Additionally, another circuit that encourages social interaction was turned off by sleep deprivation, worsening the problem.

However, the feeling of loneliness and social isolation doesn't have to last forever. "On a positive note, just one night of good sleep makes you feel more outgoing and socially confident, and furthermore, will attract others to you." Walker said.

Not only can lack of sleep affect your social life, but it can also make you angrier.

Research from Iowa State University says even losing just a couple hours of sleep a night can make you angrier.

"Despite typical tendencies to get somewhat used to irritating conditions — an uncomfortable shirt or a barking dog — sleep-restricted individuals actually showed a trend toward increased anger and distress, essentially reversing their ability to adapt to frustrating conditions over time," said Zlatan Krizan, professor of psychology at Iowa State.

Krizan's team divided participants into two groups — one group that continued their normal sleep routine and the other group that slept two to four hours less for two nights in a row. Both groups were subjected to different sounds before and after sleep and rated them.

"In general, anger was substantially higher for those who were sleep restricted," Krizan said. "We manipulated how annoying the noise was during the task and as expected, people reported more anger when the noise was more unpleasant. When sleep was restricted, people reported even more anger, regardless of the noise."

This story was originally published in May 2014 and has been updated with new information.

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.

Skipping sleep isn’t just bad for your health — it screws up your social life, too
Several studies reveal what sleep deprivation can do to a person, and it’s not pretty.