What Is Sleep Quality?

Written by Jill Zwarensteyn, Editor

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In This Article

The quality of sleep isn’t solely determined by the duration of hours spent in slumber, but also by how effectively your body can go through its sleep cycle. Continue reading for more details.

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Whether you’ve discussed your sleep habits with your doctor or have been looking online for ways to improve your sleep, the term “sleep quality” has likely come up. Sleep quality refers to a measurement of how well (or not so well) you are sleeping. Of course, many different factors can affect your sleep quality, along with varying ways to evaluate your quality of sleep. 

In this article, we’ll detail how sleep quality is measured, what can impact your sleep quality, and how to achieve better sleep quality. Ultimately, our goal is not only helping you get more hours of rest but better overall sleep quality so that you feel rested, energized, and ready to take on the day.

How Do You Measure Sleep Quality?

The most popular sleep quality metrics¹ currently available revolve around measuring brain waves during sleep, heart rate variability (HRV), and levels of hormones such as cortisol and melatonin.

Brain waves can be measured by EEG machines² that use sensors attached to your head to determine what stage of sleep you are in. As you go through each stage of sleep, there is a shift in the frequency and amplitude of brain waves³. The most important states to measure for determining sleep quality are REM and deep sleep; however, it can be useful to get more information on all stages of your sleep cycle.

There are some rudimentary EEG machines available to buy, however, EEG machines are usually used in clinics during overnight sleep studies. 

Heart rate variability⁴ is a bit easier to measure at home, as it can be ascertained through various devices such as belts worn around your chest or smartwatches. Heart rate variability occurs when the amount of time between your heartbeats fluctuates a little bit.⁴ Having a heart that is highly variable is a good thing, as it means your body can adapt to many kinds of changes. 

People with higher heart rate variability tend to be less stressed.⁴ That said, heart rate variability should be lower during sleep as the body relaxes for rest.⁴ 

Certain hormones also contribute to sleep quality. Gathering data on hormones can be done through simple saliva, urine, or blood tests which measure the levels of melatonin (a hormone responsible for inducing sleep) and cortisol (a hormone associated with stress).

Saliva tests, such as the kind that can be done at home through a self-test kit, are easy to use and widely available. Blood and urine tests are typically done in a lab or doctor’s office. The best way to measure hormones like melatonin⁵ and cortisol is typically a blood test, so if you’re looking for the most accurate results, it might be best to make an appointment with your doctor.

What is the Pittsburgh Sleep Quality Index?

The Pittsburgh Sleep Quality Index⁶ (PSQI) is a method of measuring sleep quality and patterns by evaluating seven different components:

1. Subjective sleep quality
2. Sleep latency (the time it takes to fall asleep)
3. Sleep duration
4. Habitual sleep efficiency (ratio of time spent sleeping vs. time intended for sleeping)
5. Sleep disturbances
6. Use of sleeping medication
7. Daytime dysfunction.

The subjective component of the PSQI test gives you a better idea of how you feel during the day and your general mood by asking questions such as “How restful was your sleep last night?” or “How would you rate your sleep quality?”.

The next part of the test looks at sleep latency⁷, which is an important predictor of how likely you will develop a sleep disorder. Sleep latency is the amount of time it takes for you to fall asleep after turning off the lights and trying to sleep.

Next, the test asks about sleep duration and efficiency. While sleep duration is how long you sleep, sleep efficiency⁸ is the ratio of total time spent asleep to time in bed. 

The PSQI also evaluates specific sleep disturbances, including insomnia, excessive waking after going to bed, and taking more than 30 minutes to fall asleep on average every night. This test, which you can access online⁹, is useful for examining how your sleep patterns affect your overall health by looking at other measures such as heart rate variability.

What are the Factors that Affect Sleep Quality?

There are many factors that can influence how well we sleep, and while we can’t change some of these factors, making certain lifestyle modifications could help. 

• Age – Research¹⁰ shows that sleep problems are more common in older adults than younger adults. As we age, we experience a decrease in melatonin production¹¹. Melatonin is a naturally occurring hormone that promotes sleepiness, so of course, the less you produce, the less tired you may feel. Other reasons older adults may struggle to sleep well include pain caused by arthritis, a decrease in physical activity, and a natural shift in the body’s internal clock.¹⁰ 

• Sex – Insomnia is up to two times more common¹² in females than it is in males. This discrepancy between the sexes is often because of societal differences between men and women, however, it is also largely due to hormonal differences.¹²

• Hormones – Women tend to have more irregular hormone levels than men, especially during their menstruation years. This hormonal fluctuation throughout the month may lead to sleep disturbances which can be made worse by stress levels.¹² Additionally, hormones fluctuate and can cause sleep disturbances during perimenopause and into menopause. 

• Fitness level – Evidence shows that exercising regularly¹³ helps people fall asleep more quickly and improves their overall sleep quality. In fact, just 30 minutes of exercise a day could improve sleep quality.¹³ 

• Stress – When people are under stress it is common for them to experience many different health problems, including trouble sleeping¹⁴. This difficulty in sleeping is due to an elevation in stress hormones, like cortisol, which disrupts sleep.¹⁴ 

• Diet – According to research, the foods you eat¹⁵ could impact how well you sleep. More specifically, people who consume more foods with tryptophan, tart cherries, and dietary supplements like zinc could see improvements in their sleep.¹⁵ 

• Health conditions – Certain health conditions¹⁶ can contribute to a person’s risk for developing insomnia, including depression, heart problems, other sleep disorders, and pain. We’ll also go over additional health conditions that can affect sleep in further detail below.

• Environment – Poor sleep quality may be related to external factors in the environment that interfere with sleep, such as noise or discomfort. If you live in a noisy environment, you may find it difficult to fall and stay asleep. Similarly, if you’re sleeping on a poor-quality mattress, you may find yourself tossing and turning for longer in the night.

• Caffeine intake – According to the American Academy of Sleep Medicine, caffeine has a half-life of three to five hours¹⁷. The term “half-life” refers to how long it takes your body to eliminate half of the substance. In this case, it means that caffeine can still remain in your system after five hours. Therefore, it’s best to keep your caffeine intake to earlier in the day (ideally just the morning), so that it’s less likely you’ll have any left in your system when it’s time for bed.
• Alcohol consumption – Alcohol is a depressant¹⁸, which means it slows down brain function and neural activity. Even though alcohol can make you fall asleep faster, it disrupts sleep quality, especially during the second half of the night¹⁹.
• Nicotine intake – Like caffeine, nicotine is a stimulant. This means it speeds up brain function and can make it hard to fall asleep and stay asleep. Research shows that cigarette smoking²⁰ negatively impacts sleep quality overall, so if you are having trouble sleeping, it may be a good idea to quit. If you can’t, try not to smoke at least two hours before bedtime and preferably not within one hour of going to sleep.

• Medications – Certain medications, such as antidepressants, those for epilepsy, and steroids could lead to insomnia.¹⁶ Make sure you talk to your doctor if you think one of your medications is inhibiting your sleep.

• Sleep cycle – Each night we cycle through multiple sleep cycles, which last about 90 minutes. Each cycle is made up of four stages. Did you know, though, that the sleep stage you wake up in could impact how rested you feel? 

The first two stages in a sleep cycle, NREM 1 and NREM 2, are a light sleep. Ideally, you’d want to wake up at the top of a cycle in a light sleep. However, waking up in NREM 3 or REM sleep, which are the final two stages, could leave you feeling groggy and less rested.

What is the Best Time Range for Quality Sleeping?

A recent study conducted by U.K. Biobank²¹ suggests that our circadian rhythm is best suited for going to sleep between the hours of 10:00 p.m. to midnight. The researchers concluded that deviations from this schedule could reduce sleep quality significantly, and increase the risk for cardiovascular disease, especially among women.²¹

However, keep in mind that this study is based on mainly recollection-based data collection, which can be difficult to verify given our forgetful nature as humans. The best time to go to sleep may be subjective.

Some people can go to bed at midnight regularly and wake up feeling refreshed and ready for the day early in the morning, while others may need to get in bed at 10:00 p.m. just so they can get a good night’s sleep. Either way, you should aim to get between seven and nine hours of sleep, though, and plan to go to sleep at a time that allows for this.

The best way to ensure you’re getting a good night’s sleep is to follow a regular schedule of going to bed and waking up at the same time every day, including weekends. This helps establish a rhythm that trains your body clock to know when it’s time for sleep and when it’s time for wakefulness.

What Health Conditions Are Linked to Poor Sleep Quality?

Certain health conditions can cause sleep disturbances and poor sleep quality, both directly and indirectly. 

• Thyroid dysfunction– Hypothyroidism²² is a condition in which the thyroid gland cannot produce enough thyroid hormones, including thyroxine (T4) and triiodothyronine (T3), which play roles in various bodily functions, including sleep regulation. A lack of thyroxine can lead to chronic fatigue and sleep disturbances. Likewise, when there is an abundance of thyroxine due to hyperthyroidism, this can create a feeling of being “keyed up” or hyper and can make getting to sleep and staying asleep equally difficult.²² 
• Heart disease – People who have heart failure or other conditions that cause heart arrhythmias may find it difficult to fall asleep because of the changes in their heart rate. According to research²³, 23 to 73 percent of people with heart failure deal with chronic insomnia. 
• Cancer – Cancer treatments²⁴ often lead to problems with sleep. People who are undergoing chemotherapy or radiation treatments often experience fatigue, insomnia, loss of appetite, depressed moods, and pain – all symptoms that can negatively affect sleeping patterns.²⁴
• Diabetes – According to recent findings²⁵, diabetes and sleep apnea have a bidirectional relationship, in that people with Type 2 diabetes have a higher risk of sleep apnea, and people with sleep apnea have a higher risk of developing diabetes. Sleep apnea is a sleep disorder in which your breathing is interrupted while you sleep, and it can lead to other health problems as well as daytime fatigue.

How to Improve Sleep Quality

In some cases, more formal treatment may also be needed to improve sleep quality, especially if you’re dealing with a certain medical condition or sleep disorder. However, for many people, simply forming better sleep habits could yield positive results.

• Get physically active – Research shows getting regular physical activity can lead to better sleep quality.¹³ If you don’t already have a regular fitness routine, it’s best to start slow with low-impact activities and work your way up. Walking, biking, and swimming are great low-impact, aerobic exercises. Additionally, weight training and resistance exercises could also help improve sleep quality²⁶.

• Manage stress – High levels of stress have been shown to cause problems with sleeping patterns, so managing your stress is one of our best tips to increase sleep quality¹⁴. Try introducing some meditation, yoga, or deep breathing throughout the day and before bed. Avoiding caffeine, alcohol, and heavy meals close to bedtime can also help.
• Keep a sleep schedule – Going to bed and waking up at the same time every day can be a key factor in improving your sleep quality. Try going to bed about 30 minutes earlier each night until you fall asleep easily, and you’ll soon have a better idea of when you should start getting ready for bed.
• Fix any problems in your bedroom – Having a comfortable sleep environment is key to falling asleep faster and maintaining good sleep quality. Your ideal sleep environment should be cool, dark, and completely quiet. 

What items do you need for a night of good sleep?

If falling asleep or staying asleep is difficult for you, there are certain items you can use to help – especially if you live in an urban area with more lights or sound pollution. 

• Comfortable mattress and pillow – Most mattresses should last between seven and 10 years, depending on how well you take care of them. You can extend the life of your mattress by rotating it monthly – turn it head-to-foot so the weight is distributed evenly throughout its life. However, if your mattress is sagging or causing you pain, it may be time to invest in a replacement.
• Air filter – If you’re having trouble breathing or allergies are a problem at night, an air filter could help by removing allergens and improving air quality. However, it’s important to maintain a comfortable room temperature as extreme temperatures can disrupt sleep.
• White noise machine – A white noise machine can mask pesky noises that keep you awake, and it can also provide a calming routine that lulls you to sleep, training your mind to know when it’s time for rest.
• Earplugs – If white noise isn’t doing the trick, you may want to invest in a pair of moldable earplugs to drown out the sound of traffic, pets, or a snoring partner.
• Eye mask – Your bedroom should be as dark as possible, but in the event outside light is still peeking into your bedroom, an eye mask could help block out that light. 
• Weighted Blanket – A weighted blanket can be helpful for people who have poor sleep quality because of anxiety. The “deep pressure stimulation” created by the blanket calms the nervous system and may even increase melatonin production²⁷, helping you feel more sleepy.  

Learn more: How to Choose a Mattress

References:

1. de Zambotti PhD, Massimiliano., et al. “Sensors Capabilities, Performance, and Use of Consumer Sleep Technology”. National Library of Medicine. 2020. 
2. “EEG (electroencephalogram)”. Mayo Clinic. Last modified May 11, 2022. 
3. Patel, Aakash K., et al. “Physiology, Sleep Stages”. National Library of Medicine. Last modified September 7, 2022. 
4. “Heart Rate Variability (HRV)”. Cleveland Clinic. Last modified September 1, 2021. 
5. Rzepka-Migut, Beata., Paprocka, Justyna. “Melatonin-Measurement Methods and the Factors Modifying the Results”. National Library of Medicine. 2020.  
6. “Pittsburgh Sleep Quality Index”. University of Pittsburgh. 1989. 
7. “Sleep Latency”. ScienceDirect. Webpage accessed July 11, 2024.  
8. Reed PhD, David L., Sacco PhD, William P. “Measuring Sleep Efficiency: What Should the Denominator Be?”. National Library of Medicine. 2016.
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10. “Sleep disorders in the elderly”. Mount Sinai. Webpage accessed July 11, 2024. 
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18. Vezali Costardi, João Victor., et al. “A review on alcohol: from the central action mechanism to chemical dependency”. National Library of Medicine. 2015. 
19. Thakkar, Mahesh M., Sharma, Rishi., Sahota, Pradeep. “Alcohol disrupts sleep homeostasis”. National Library of Medicine. 2015.  
20. Liao, Yanhui., Xie, Liqin., et al. “Sleep quality in cigarette smokers and nonsmokers: findings from the general population in central China”. BMC Public Health. 2019. 
21. Nikbakhtian, Shahram., et al. “Accelerometer-derived sleep onset timing and cardiovascular disease incidence: a UK Biobank cohort study”. Oxford Academic. 2021. 
22. Green, Max E., Bernet, Victor., Cheung, Joseph. “Thyroid Dysfunction and Sleep Disorders”. National Library of Medicine. 2021. 
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25. Huang, Tianyi., et al. “A Population-Based Study of the Bidirectional Association Between Obstructive Sleep Apnea and Type 2 Diabetes in Three Prospective U.S. Cohorts”. National Library of Medicine. 2018.  
26. Kovacevic, Ana., et al. “The effect of resistance exercise on sleep: A systematic review of randomized controlled trials”. National Library of Medicine. 2018.  
27. Meth, Elisa., et al. “A weighted blanket increases pre-sleep salivary concentrations of melatonin in young, healthy adults”. National Library of Medicine. 2024. 

Jill Zwarensteyn

Editor

About Author

Jill Zwarensteyn is the Editor for Sleep Advisor and a Certified Sleep Science Coach. She is enthusiastic about providing helpful and engaging information on all things sleep and wellness.

Combination Sleeper