If you read the news and believe all the sensationalist headlines, you're probably under the impression that mankind is going through a stage of chronic sleep deprivation. That may not be the case, though.
Although some studies have suggested that average sleep duration has declined over the last few decades, others have cast doubt on such findings.
As a result of this, researchers set out to conduct a review of literature published from 1960 to 2013 to see if sleep duration really has been in decline.
Their review involved 168 studies with 257 data points representing over 6,000 individuals between 18 and 88 years of age.
After analyzing the data, researchers concluded that there was no significant association between sleep duration and the study year .
In other words, over the last half-century, objectively-recorded sleep durations remained relatively stable . This remained the case even when comparing sleep durations across age groups and genders.
Furthermore, sleep duration still remained stable regardless of whether data was collected from actigraph units or from sleep studies, or whether study participants were assessed during fixed sleep schedules or their usual sleep schedules.
So what does this mean for the general assumption that we're experiencing a modern epidemic of insufficient sleep?
Well, it's worth highlighting the limitations of the literature used in this review.
1. The ethnic and racial composition of participants in most studies were probably not representative of the general population.
In particular, it's thought that shorter sleep durations are more common in black individuals compared to white individuals. Furthermore, it has been suggested that the prevalence of shorter sleep durations is increasing more among blacks compared to whites.
2. Most of the studies excluded women or did not separate data between genders.
3. Other factors that have been associated with sleep duration such as employment and socio-economic status, career, and education were also not reflected in many of the study samples.
4. Most studies were conducted in sleep labs. Sleep studies many not be able to adequately record a decline in sleep duration that may be occuring at home, but not in a lab environment.
Furthermore, sleep studies generally limit sleep periods to eight hours. Therefore, if participants used to get more than eight hours of sleep, but this fell to less than eight hours over time, these studies would not have been able to record the decline.
Finally, sleep studies tend to record sleep over a set period of time - not a 24 hour period. Therefore, naps (which should be included in sleep duration figures) go unrecorded.
5. Older studies did not screen for other sleep disorders such as sleep apnea. Therefore, earlier studies may have resulted in lower estimates of sleep duration compared to newer studies.
What was particularly interesting about this review was the finding that if the optimal objective sleep duration for adults is between six and six-and-a-half hours, more participants are at risk due to too much sleep rather than not enough sleep .
Here are a few theories:
1. Increased public awareness about sleep
More of us are aware of the importance of sleep. Consequently, we have seen a rise in the number of sleep disorder diagnoses, and an explosion in the availability (and use) of sleeping pills. This may have influenced our perception.
An increase in knowledge about sleep has also led to individuals paying more attention to their sleep. Being aware of the amount of time spent asleep versus the amount of time spent in bed could also create the perception that we're now getting less sleep than we used to.
2. Sleep is still associated with leisure
Although sleep education has increased, we still tend to associate sleep with leisure and relaxation. As life becomes increasingly stressful and we feel more intense time pressures, we may feel we have less time for sleep even if we're still getting precisely the same amount of sleep as we always have.
3. Depression rates are on the rise
Poor or inadequate sleep is associated with depression. Therefore, as depression rates increase, there are more complaints of insufficient sleep.
4. Cultural influence
As we continue to hear that we're a sleep deprived society, we begin to believe it. Our perception of sleep is influenced by reports from the media and sleep scientists.
The fact of the matter is this:
The evidence tells us that sleep durations are not in decline.
Furthermore, you're probably getting more sleep than you think you are.
Source: Sleep Medicine Reviews
Last updated: July 22, 2016