The definition of healthy sleep depends on several factors, such as duration and how many times a person awakens during the night. The quality of sleep is subjective and also includes sleep satisfaction, how much time a person spends in bed compared to sleep time and alertness after sleeping. Research shows that poor sleep is associated with physical and mental health, including heart disease, obesity, diabetes, hypertension and depression.
Research Spotlight
The databases often return hundreds of medical studies for a single wellness approach. This section summarizes a sampling of five studies – providing just a taste of the available research. These Spotlights were not selected because they are the most favorable or the most recent, but to provide you an introduction to the more extensive research you’ll uncover searching the four databases found in the “Research” section of this site.
- Study: Sleeping with Even the Dimmest Light Raises Blood Sugar and Heart Rate
A new study from Northwestern University found that sleeping in even the dimmest light for one night (such as leaving the TV on or exposure to streetlights through a window) significantly impaired cardiometabolic function: increasing nighttime heart rate and next-morning insulin resistance. The researchers concluded that even when your eyes are closed, your brain knows that lights are on, with dim light activating the sympathetic nervous system and disturbing circadian rhythms.
Access this study on sleep health - Just One Night of Bad Sleep Harms Your Wellbeing–At Six Nights Toll Is Severe
A 2021 study (2,000 US adults) found that just one night of less than six hours of sleep significantly hurts mental and physical wellbeing, and as the number of consecutive days of sleep loss increase, the severity of emotional and physical issues (body aches, gastrointestinal issues and respiratory problems) become severe. Problems spiked on day three and plateaued until day six, when mental and physical health significantly deteriorated.
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- Weighted Blankets Help with Insomnia
A 2020 study from Swedish researchers found that people with depression and other mental health issues slept much better through the night when using a weighted blanket. At the end of the trial, 42% of those that slept with an 18-pound blanket scored so low on the Insomnia Severity Index to be considered in remission from their sleep troubles, compared with 3.6% of the control group. The weighted blankets didn’t have a significant effect on total sleep time, but led to a significant decrease in waking after sleep, less daytime sleepiness and fewer symptoms of depression and anxiety.
Access this study on sleep health - Artificial Light at Night Linked to Mood Disorders in Teens
A large 2020 study from the NIH (10,123 US teens) is the first to show that exposure to outdoor, artificial light at night negatively impacts teens’ mental health. Teens exposed to higher levels of nighttime light are more likely to have a mood disorder (including anxiety and bipolar disorder and phobias). This adds to the evidence that disruptions to circadian rhythms contribute to certain mental disorders. The findings also show that teenagers who belong to racial/ethnic minority groups or who come from lower-income families are more likely to live in areas with high levels of outdoor light at night, so are more at risk.
Access this study on sleep health - Poor Sleep Increases Risk for Heart Disease, Stroke & Atherosclerosis
A major 2020 study (1,600 participants) from the University of California Berkeley explains why disrupted nightly sleep and clogged arteries are pathologically intertwined. It’s the first study to show that fragmented sleep is associated with a unique pathway—chronic circulating inflammation throughout the bloodstream—which, in turn, is linked to higher amounts of plaques in coronary arteries that can result in fatal heart disease.
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- Loss of Just One Night’s Sleep Ups Tau Protein Associated with Alzheimer’s
A 2020 exploratory study from Uppsala University (Sweden) found that the loss of just one night’s sleep in young, healthy men significantly increased the level of tau protein (up 17 percent) in the blood, which is associated with the risk of developing Alzheimer’s disease.
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Scientists Underestimated Dangerous Effects of Sleep Deprivation
One of the largest sleep studies ever (Michigan State University, 2019) revealed that sleep deprivation has a much more negative effect than earlier studies indicated. Prior studies showed how too little sleep hurts a person’s ability to maintain attention, but this one also examined how it impacts placekeeping, the ability to complete a series of steps without losing one’s place. The impact, researchers said, is “startling”: Sleep deprivation doubles the odds of making placekeeping errors and triples the number of lapses in attention.
Access this study on sleep health - The More Polluted the Air We Breathe, The Less Productive We Become
A 2019 observational study from Brandeis University showed a strong connection between the simple act of walking and better snoozing: middle-aged men and women who took about 7,000 steps a day experienced significantly better sleep quality across a variety of measures.
Access this study on sleep health - People Who Nap 1-2 Times a Week 48 Percent Less Likely to Have Heart Attack
A 2019 observational study from University Hospital of Lausanne, Switzerland (tracking 3,462 people for 8 years) found that napping once or twice a week (for between five minutes and an hour) was associated with a 48 percent lower risk of heart attack, stroke or heart failure than those who did not nap.
Access this study on sleep health - Screen Time Before Bed Significantly Impairs Children’s Sleep
A 2019 study from British researchers (analyzing 6,616 children) found that using screens in the hour before bedtime hurts kids’ sleep and quality of life measures. Before-bed screen time was associated with a significantly worse ability to fall asleep as well as waking up too early (60% higher odds). And using screens in a dark room led to even worse sleep outcomes than using them with the lights on.
Access this study on sleep health - Six to Eight Hours a Night the ‘Sweet Spot’ for Healthy Sleep
A large, 2018 study in the European Heart Journal (116,632 people across 21 countries) found that getting at least 6-8 hours of sleep a night is optimal, but more might not be. People who slept 8-9 hours had a 5% increased risk for cardiovascular disease or death; those who slept 9-10 hours had a 17% increased risk; and those sleeping more than 10 hours boosted their risk by 41%. A possible reason: people have underlying conditions causing them to sleep longer.
Access this study on sleep health - Sleep, Exercise and Limits on Screen Time Boost Kids’ Brainpower
A 2018 study (on 4,524 children ages 8-11) from Canada’s Healthy Active Living & Obesity Research Group found that 9–11 hours of sleep a night, one hour of exercise, and a limit of fewer than two hours a day of recreational time in front of screens were associated with higher mental test scores for children (from memory to language skills to the ability to plan).
Access this study on sleep health - Good Sleep Tied to Lower Risk of Metabolic Problems for Teens
A 2018 study from Harvard and other researchers, tracking 829 teens for sleep time and quality, found that a good night’s sleep seems crucial for teens’ metabolic health. Shorter sleep time was associated with higher glucose levels, systolic blood pressure and triglycerides and lower HDL cholesterol – all signs of poor metabolic health. While other studies have linked bad sleep with obesity, this study is notable because the bad metabolic indicators were independent of BMI.
Access this study on sleep health - Weekend Sleep-Ins Lower Mortality Risk
A 2018 Stockholm University and Karolinska Institute survey of 38,000 adults indicated that people getting five hours of sleep or less a night have a 65% higher mortality rate than those that consistently get 6-8. But that weekend sleep-in seems to cancel out the mortality risk: people who only got a few hours of sleep during the week, but then had a regular long weekend snooze, had no greater risk of early death than those people that consistently slept 6-8 hours a night.
Access this study on sleep health - Disrupted Body Clock Linked to Various Mood Disorders
A large 2018 study (91,000 people) from Lancet Psychiatry found that people with a disrupted body clock (highly active at night or inactive in the day) had higher rates of major depression, bipolar disorder, more loneliness, lower happiness, worse reaction times and more mood instability.
Access this study on sleep health - Poor Sleep Associated with Increase in Brain Protein Linked to Alzheimer’s
A 2018 study from the NIH and Yale indicated that sleep deprivation is linked to higher levels of the protein beta-amyloid—a well-known precursor to Alzheimer’s disease. Nineteen out of 20 participants had higher beta-amyloid in their brains after a night of exhaustion. And while a small study, it’s important because it’s the first of its kind to test human beings in a controlled setting.
Access this study on sleep health - Lack of Sleep Leaves Brain Cells Sluggish
A small 2017 study (UCLA, Tel Aviv Univ. etc.) indicates that when people don’t get enough sleep, their brain cells literally slow down. Researchers found sleep deprivation results in the bursts of electrical activity that brain cells use to communicate to become slower and weaker – which can lead to mental lapses that affect not only perception but memory.
Access this study on sleep health - Children Who Sleep Less at Higher Risk for Type 2 Diabetes
A study from British researchers (2017) on 4,525 9- and 10-year olds found that less sleep leads to higher body mass index, higher insulin resistance, and higher glucose readings for children – all key risk factors for Type 2 diabetes. Increasing weekday sleep duration by an hour was associated with a 0.2 lower B.M.I. and a 3% reduction in insulin resistance. The lead author noted that, “for children, the more sleep the better — there is no threshold.”
Access this study on sleep health - With Severe Sleep Deprivation, Brains of Mice Began to “Eat Themselves”
A 2017 study from Marche Polytechnic University (Italy) conducted on mice showed that severe sleep deprivation caused the brain to feed off its own neurons and synaptic connections – the result when cells like astrocytes go into overdrive. Researchers noted that this could explain why chronic lack of sleep could put people at risk of Alzheimer’s and other neurological disorders.Access this study on sleep health - Meta-review: Too Little Sleep Leads to Overeating the Next Day
A meta-analysis of 11 sleep studies from King’s College London (2016) found that after a night of too little sleep (around 4 hours), people, on average, consumed 385 extra calories the next day – and they also consumed more fat and less protein.Access this study on sleep health - Young Children With Early Bedtimes Half as Likely to Become Obese
A study by Eunice Kennedy Shriver National Institute of Child Health (of 1,000 children) found that preschool kids that are in bed by 8 pm are half as likely to be obese in their teen years. Among children who were in bed by 8 p.m., 10% were obese as teens, compared to 16% of those who went to bed between 8 and 9, and 23% of those who went to bed after 9.
Access this study on sleep health - Sleep Problems Linked to Diabetes in Men
A study conducted by several European medical schools (2016) indicated that men that don’t get enough sleep, or get too much, show an increased risk for Type 2 diabetes. The study tested men and women, measuring their sleep duration (7 hours on average) and markers for diabetes (how well pancreatic cells take up glucose and how sensitive body’s tissues are to insulin). When men got too little or much sleep, their glucose tolerance decreased – although no such association was found in women. The researchers weren’t sure why the results were gender-specific, but cautioned that because it was a cross-sectional study – conclusions weren’t drawn about cause and effect.
Access this study on sleep health - Low Fiber, High-Fat & High-Sugar Foods Lead to Poor Sleep Quality
A small, new study by Columbia University (2016) indicates that eating low-fiber and high-fat and sugary foods leads to waking up at night and less time in “slow wave sleep,” the crucial restorative phase. If studies have shown that sleep deprivation subsequently leads to bad diet choices (which then lead to obesity and diabetes), this study suggests that bad diets are a vicious circle: unhealthy food also interferes with sleep.
Access this research on sleep health - Weight Gain Could Be Linked to Late Bedtimes
A new study from researchers at U.C. Berkeley and Columbia University suggests that with every hour of later bedtime, that Body Mass Index (BMI) goes up. Studying 3,342 adolescents from 1996-2009, they found that each hour of later bedtime on a school/work week was associated with a two-point increase in BMI. And this effect was true for people that got a full 8 hours of sleep, and was not impacted by TV time or exercise.
Access this research on sleep health - Common Sleep Medications Linked to Dementia, Alzheimer’s
A 2015 University of Washington (U.S.) population-based study found that medications with strong anticholinergic activity (which include common sleep aids like Tylenol PM, as well as certain antihistamines and anti-depressants) increase the risk of dementia and Alzheimer’s – and the longer the drugs were taken, and the higher the dose, the higher the risk. (Short-term use was not associated with any risk.) The researchers tracked 3,434 people aged 65+ with no initial dementia for eight years, using pharmacy records to track prescription and over-the-counter usage.
Access this study on sleep health - Exercise Improves Sleep Quality and Reduces Sleep Medication Use
A 2012 meta-review of six clinical trials undertaken by National Taiwan University found that 10-16 week exercise training programs (either moderate aerobic exercise or high intensity resistance exercise) resulted in significantly better global Pittsburgh Sleep Quality Index scores and significantly reduced sleep latency and medication use – for middle-aged and older adults reporting sleep problems. However, sleep duration and daytime functioning were not affected.
Access this study on sleep health - Too Little Sleep Associated with Heart Disease & Stroke
A University of Warwick (UK) systematic review of 15 studies concluded that short duration of sleep is associated with greater risk of developing or dying from coronary heart disease and stroke. Interestingly, long sleep durations are also indicators of cardiovascular outcomes.
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