The researchers behind the study found that late-middle-aged adults who reported poor sleep had more biomarkers of Alzheimer's disease in their cerebrospinal fluid.
Scientists analyzed 101 adults with an average age of just under 63 for this study (so the sample size is fairly small). Researchers collected spinal fluid samples from each participant to check for tangled protein buildups, inflammation, and damaged cells that are related to Alzheimer's.
The participants all had some increased risk for Alzheimer's due to their family history and genetic factors, but all were cognitively healthy. Researchers found that age differences within the group didn't seem to affect levels of Alzheimer's biomarkers in those studied. However, the individuals who reported not sleeping well, having sleep problems, or feeling sleepy during the day had significantly more signs of the disease in their spinal fluid.
Related: What happens if you don't get enough sleep:
27 horrible things that happen if you don't get enough sleep
27 horrible things that happen if you don't get enough sleep
1. Short term memory and learning problems
Sleepiness has long been a problem for students. One study of middle school kids found that "delaying school start times by one hour, from roughly 7:30 to 8:30, increases standardized test scores by at least 2 percentile points in math and 1 percentile point in reading." Sleep researchers say that teens, who naturally tend to become night owls, suffer even more from early start times. But it's not just kids. Sleep deprivation also wrecks adults' short-term memory, according to one study that found cutting sleep short significantly impaired the ability of adult volunteers to remember words they'd been shown the day before. In another study, researchers found that while people tend to improve on a task when they do it more than once, this isn't true if they are kept awake after they try it the first time — even if they sleep again before doing it again.
"Complaints of irritability and [emotional] volatility following sleepless nights" are common, a team of Israeli researchers observed. They put those complaints to the test by following a group of sleep-deprived medical residents. The study found that the negative emotional effects of disruptive events — things like being interrupted while in the middle of doing something — were amplified by sleep loss.
Poor sleep quality is strongly correlated to chronic skin problems, according to some research out of the University of Wisconsin. Other research has shown that people who don't sleep well or sleep five hours a night or less have a harder time recovering from skin damage caused by ultraviolet light exposure and by having tape taken off of their skin. When researchers compared those participants to people who slept well, they found more signs of skin aging in poor sleepers.
People who don't get enough sleep have a harder time resisting high-calorie foods, more cravings for unhealthy meals, and a hard time controlling their impulses. Researchers think going without sleep causes hormonal imbalances that are responsible for this, imbalances they link to a high body mass index and obesity.
One 2015 study found that sleep helps cleanse the brain of the beta-amyloid protein that can build up while you are awake. That protein is strongly associated with Alzheimer's disease, and researchers say that this process can lead to a vicious cycle, since the more beta-amyloid there is in the brain, the harder it is to get to a cleansing deep sleep state.
Sleep deprivation is associated with tunnel vision, double vision, and dimness. The longer you are awake, the more visual errors you'll encounter, and the more likely you are to experience outright hallucinations.
When researchers kept people awake for 88 hours, their blood pressure went up — no big surprise there. But even subjects who were allowed to sleep for 4 hours a night had an elevated heart rate when compared to those getting 8 hours. Concentrations of C-reactive protein, a marker of heart disease risk, increased in those fully and partially deprived of sleep.
Your reaction time is severely impeded when you don't get enough sleep. When researchers gave West Point cadets two tests that require quick decision-making, some were allowed to sleep between the tests, while others were not. Those who had slept did better the second time — those who had not did worse, and their reactions slowed down. A study in college athletes found similar results.
You know that great thing your immune system does, where when you get an open wound of some kind it doesn't always get infected immediately? Prolonged sleep deprivation and even one night of sleeplessness can impede your body's natural defenses against infection.
In another small study that showed sleep deprivation can make vaccines less effective, 19 people were vaccinated against Hepatitis A. Ten of them got 8 hours of sleep the following night, while the rest pulled an all-nighter. Four weeks later, those who had slept normally had levels of Hepatitis A antibodies almost twice as high as those who'd been kept awake.
10. Bad decision-making in ways that put lives and finances in danger
Planning to make some changes to your portfolio? You might want to make sure you're well-rested. "A single night of sleep deprivation evoked a strategy shift during risky decision making such that healthy human volunteers moved from defending against losses to seeking increased gains," researchers concluded.
Other researchers have found that severe sleep deprivation impairs people's ability to follow pre-established procedures for making a "go" or "no-go" decision, something that researchers say contributed to the space shuttle Challenger explosion, the Chernobyl meltdown, and the Exxon Valdez disaster.
When people sleep, the body slows down its normal urine production. This is why most people don't have to pee in the night as much as they do during the day. But when someone is sleep deprived, this normal slowdown doesn't happen, leading to what researchers call "excess nocturnal urine production." This condition may be linked to bed wetting in children and, in adults, it's tied to what's called nocturia — the need to use the bathroom many times during the night.
Having trouble paying attention to what you're reading or listening to? Struggling with anything that requires you to truly focus? "Attention tasks appear to be particularly sensitive to sleep loss," researchers have noted. If you want to stay alert and attentive, sleep is a requirement. Otherwise, you enter "an unstable state that fluctuates within seconds and that cannot be characterized as either fully awake or asleep," and your ability to pay attention is variable at best.
Severe sleep deprivation seems to affect your ability to carry on a conversation — much like having way too much to drink. "Volunteers kept awake for 36 hours showed a tendency to use word repetitions and clichés; they spoke monotonously, slowly, [and] indistinctly," one study noted. "They were not able to properly express and verbalize their thoughts."
If you're wondering why you're sick all the time and seem to pick up every bug that travels around the office, it's probably because you're not getting enough sleep. When a group of 153 people were exposed to a common cold, those who had gotten less than 7 hours of sleep in the two weeks prior were almost 3 times more likely to get sick than those who'd had 8 or more hours of sleep. How well you sleep is also a factor – those who had spent 92% of their time in bed actually asleep were 5.5 times more likely to catch a cold than those who had been peacefully slumbering 98-100% of the time they were in bed.
Lack of sleep causes hormonal changes that make it harder for your body to build muscle and heal. This makes it harder to recover from the muscle damage caused by exercise and worsens conditions related to muscle atrophy. Other research has also shown the reverse — your body releases growth hormone and heals damage during sleep, which is why fitness advocates will always point out that sleep is an essential for getting into shape.
Drowsy driving is often compared to drunk driving: You really shouldn't do either. "Motor vehicle accidents related to fatigue, drowsy driving, and falling asleep at the wheel are particularly common, but often underestimated," one review concluded. Pilots, truck drivers, medical residents, and others required to stay awake for long periods of time "show an increased risk of crashes or near misses due to sleep deprivation."
Testosterone is an important component of sexual drive and desire in both women and men. Sleeping increases testosterone levels, while being awake decreases them. Sleep deprivation and disturbed sleep, consequently, are associated with reduced libido and sexual dysfunction, and people suffering from sleep apnea are at particular risk.
People in pain — especially those suffering from chronic pain — tend not to get enough sleep. This makes sense: Pain can wake you up in the night and make it hard to fall asleep in the first place. But recently, researchers have begun to suspect that sleep deprivation may actually cause pain or at least increase people's sensitivity to pain. One study found that after research subjects were kept awake all night, their pain threshold — the amount of painful stimulus they were able to endure — was lower.
19. Type-2 diabetes risk — even for non-overweight people
Being awake when your body wants you to be asleep messes with your metabolism, which in turn increases your risk for insulin resistance (often called "pre-diabetes") and type 2 diabetes. "Interventions to extend sleep duration may reduce diabetes risk," one study in adolescents concluded. And four large studies in adults found a strong association — though not a cause-effect relationship — between regular sleep loss and the risk of developing diabetes, even after controlling for other habits that might be relevant.
Most people notice that when they're sleepy, they're not at the top of their game. One study found that one sleepless night contributed to a 20-32% increase in the number of errors made by surgeons. People playing sports that require precision — shooting, sailing, cycling, etc. — also make more mistakes when they've been awake for extended periods of time.
Scientists are just beginning to investigate the relationship between sleep and cancer, and different kinds of cancer behave differently. But since disrupted circadian rhythm and reduced immunity are direct results of sleep deprivation, it's no surprise that preliminary research seems to indicate that people who don't get enough sleep are at increased risk for developing certain kinds of cancer, most notably colon and breast cancers.
Sleep disruptions in the elderly can lead to structural changes in the brain that are associated with impaired long-term memory — and sleep-related memory deficits have been observed in the general adult population as well. As early as 1924, researchers noticed that people who slept more forgot less.
A 2013 study shed some light on why sleep is tied to so many different aspects of our health and wellness. Poor sleep actually disrupts normal genetic activity. After one week of sleeping less than 6 hours per night, researchers found that more than 700 genes were not behaving normally, including some that help govern immune and stress responses.
Some genes that typically cycle according to a daily (circadian) pattern stopped doing so, while others that don't normally follow a daily pattern began doing so. What does this mean? Just one week of less-than-ideal sleep is enough to make some of your genetic activity go haywire.
In a classic study led by Nobel Prize-winning psychologist Daniel Kahneman, a group of 909 working women kept detailed logs of their moods and day-to-day activities. While differences in income up to $60,000 had little effect on happiness, a poor night's sleep was one of two factors that could ruin the following day's mood. (The other was tight deadlines at work.)
Another study reported higher marital happiness among women with more peaceful sleep, although it's hard to say whether happy people sleep better, better sleep makes people happier, or — most likely — some combination of the two. Insomniacs are also twice as likely to develop depression, and preliminary research suggests that treating sleep problems may successfully treat depressive symptoms.
One in 250 Americans suffer from Inflammatory Bowel Disease (IBD), and sleep deficiencies make its symptoms much worse. Regular sleep loss also makes you more likely to develop both IBD and inflammatory bowel syndrome, which affects an estimated 10-15% of people in the U.S. And patients with Crohn's disease were twice as likely to experience a relapse when they weren't getting enough sleep.
Many health problems are associated with sleep deprivation and poor sleep, but here's the big one: People who consistently do not get 7-8 hours of sleep are more likely to die during a given time period. Put more simply: We all die eventually, but sleeping too little — or even too much — is associated with a higher risk of dying sooner than you otherwise might.
It's impossible to say at this point whether poor sleep is causing the increase in Alzheimer's markers, or whether the fact that these individuals' brains are changing is what's causing them to have poor sleep. In fact, both are likely true — not getting enough sleep could increase Alzheimer's risk, and the factors in the brain that lead to Alzheimer's probably make it hard to get good sleep.
The researchers behind the study say that better measures of sleep quality and sleepiness during the day could help scientists learn more about the relationship between Alzheimer's and sleep.
At the same time, they write that improving sleep should be considered a priority since it might be a way to stave off cognitive decline.
"[S]leep health may be a tractable target for early intervention," they concluded in the study.
In an accompanying commentary published alongside the study, two other doctors — Adam Spira of Johns Hopkins University and Dr. Yo-El Ju of Washington University — emphasized the potential benefits of facilitating better sleep.
"Effective interventions are available to treat causes of poor sleep, so identifying and treating sleep disturbances in preclinical [Alzheimer's disease] may be a critical strategy to prevent or delay impending cognitive decline," they wrote.
That should be some serious motivation to try to get more sleep.
This file photo dated 04 November, 1991 shows US President Ronald Reagan giving a speech at the dedication of the library bearing his name in Simi Valley, California. He was US president from 1981 to 1989 and retreated from public life after it was revealed he was suffering from Alzheimer's disease. (Photo by J. David Ake, AFP/Getty Images)
Glenn Campbell performs during The Goodbye Tour at the Ryman Auditorium on January 3, 2012 in Nashville, Tennessee. (Photo by Ed Rode/Getty Images)
Picture dated 18 May 1991 of US actor Charles Bronson during the 44th Cannes film festival, southern France. Bronson died 30 August 2003 in Los Angeles of complications from pneumonia. (Photo by Gerard Julien, AFP/Getty Images)
392653 01: Actor Burgess Meredith performs in the television show 'The Twilight Zone.' (Photo Courtesy of Sci Fi Channel/Getty Images)
LOS ANGELES - AUGUST 31: Actor James Doohan recieves his star on the Hollywood Walk of Fame August 31, 2004 in Los Angeles, California. (Photo by Mark Mainz/Getty Images)
LONDON, UNITED KINGDOM - JANUARY 17: Malcolm Young of AC/DC performs on stage at Wembley Arena on January 17th, 1986 in London, United Kingdom. (Photo by Peter Still/Redferns)
NORMAN ROCKWELL'S AMERICA -- Pictured: Artist Norman Rockwell -- (Photo by: Gary Null/NBC/NBCU Photo Bank via Getty Images)
Publicity close up of Hollywood actress Rita Hayworth wearing ornately decorated gloves and holding a cigarette in a cigarette holder.
NEW YORK CITY - FEBRUARY 29: Aaron Copeland attends 10th Annual Grammy Awards on February 29, 1968 at the New York Hilton Hotel in New York City. (Photo by Ron Galella, Ltd./WireImage) (Photo by Ron Galella, Ltd./WireImage)
Actor Peter Falk poses as he arrives for the premiere of his new film
"Lakeboat" September 24, 2001 in Los Angeles. The film is an adaptation
of David Mamet's comic play about a grad student who takes a summer job
on a Great Lakes freighter and sees life through the eyes of his
low-brow crew members. The film opens in limited release in Los Angeles
September 28. REUTERS/Rose Prouser