We spend between a quarter to a third of our lives asleep, so the quality of sleep we get is important. While the term “sleep quality” is often used, there is no consensus on what it means. To address this, the National Sleep Foundation put together a group of expert panelists to determine what features indicate sleep quality. The results, published in Sleep Health, are based on a review of 277 studies, 12 possible indicators, and 9 age groups. The panel agreed that the measures below are indicators of good sleep quality. The importance of each measure is different for each age group (see table below for details).
Awakenings per night: Moments in which you wake up at night for at least 5 minutes. In general, one awakening or less indicates good sleep quality across all age groups. Older adults (over the age of 65) can wake up twice and still generally have good quality sleep.
Sleep efficiency: How long you spend sleeping compared to the total time spent in bed. For all age groups, sleep efficiency of at least 85% is a good indicator of quality sleep.
Sleep latency: The time it takes someone to fall asleep. Sleep latency under 30 minutes is generally a strong indicator of quality sleep regardless of age.
Wake after sleep onset: The amount of time you spend awake throughout the night after falling asleep. While there is not a consensus on infants, 20 minutes or less of waking after sleep onset indicates good sleep quality in preschoolers through adults. For older adults, 30 minutes or less indicates high quality sleep.
Naps in a 24-hour period: The studies reviewed by the panel did not consistently differentiate between planned naps (scheduled or regularly taken) and unplanned naps (too tired to stay awake). Due to this lack of information, the panel was unable to decide how many naps were appropriate for many age groups. The panel did agree that 4 or more naps in one day for preschoolers through adults was an indicator of low quality sleep during the previous night. But there was no consensus on how many naps indicate high quality sleep in infants, toddlers, and preschoolers. For young adults, no napping throughout the following day is a good indicator of high quality of sleep during the previous night. Teenagers however, can have a good night’s rest while still taking a single nap the following day as long as these naps are less than 20 minutes.
Nap Duration: The duration of optimal nap length for young adults has not been agreed upon, but naps greater than 100 minutes do not indicate good sleep during the previous night.
Rapid eye movement (REM) sleep: For newborns, spending about 40% or more in REM indicates good sleep quality. This figure is 21-30% for adults. However, excess REM activity does not indicate good sleep quality among adults. Some people use sleep trackers to monitor the amount of REM they are getting, but research is mixed on the accuracy of sleep trackers and apps.
Non-rapid eye movement (NREM) sleep: NREM sleep is broken further into 3 stages. N1 is the earliest stage of NREM sleep. It is generally accepted that the average person should spend 5% of their entire sleep cycle in this stage. N2 is a little more complicated and there is no complete consensus on how much time should be spent in this stage. N3 is the most definitive indicator of the three NREM stages. Experts agree that a sleep cycle that consists of 20-25% N3 is an indicator of a good night’s rest.
This is a start towards defining measures that reflect sleep quality. The panel did not reach a consensus on specifics in some categories, which leaves some things unknown such as appropriate nap length for newborns, infants, and toddlers. While these measures are indicators of good sleep, they should not be over-interpreted. For one person, a particular measure might be strongly correlated with high quality sleep. But a different measure might be most informative for another individual. For yet another person, a particular combination of these measures might be most informative. Some of the variability from one person to the next might depend on gender and age. Finally, and most importantly, these various measures are at best correlated with sleep quality. There is no scientific consensus as to whether any of these factors cause high quality sleep. With the NYU Baby Sleep Study, we are addressing the uncertainty surrounding infant sleep as we work to characterize sleep quality during the first two years of life.
The table below shows which measures indicate good sleep quality for each age group. “Appropriate” means the panel (1) agreed that the measure was a good indicator of sleep quality and (2) agreed on the amount of the measure that indicated good sleep quality. The amounts are shown below each “Appropriate”. Boxes with “Uncertain” mean the panel was unable to determine, or agree upon, how much of the measure indicated good sleep quality. “NA” means that there was not enough information available from the studies to determine whether the measure was an indicator of sleep quality.