It is correct and can be used in written English.
For example: "I recommend a minimum length of sleep of 8 hours for adults to remain healthy and alert".
Because people with narcolepsy relatively have lower levels of hypocretin or orexin produced by Hcrt cells, which is responsible in the generation of arousal and control of sleep, the person cannot control his or her sleeping pattern and the length of sleep.
A Swiss study found that the length of sleep varied with the lunar cycle, from six hours 41 minutes at full moon to seven hours at new moon.
The study shows only an association, although the link with short and long sleep both being "unhealthy" holds true with a 2011 review of evidence about the length of sleep and risk of heart disease.
Michael Breus, a clinical psychologist and sleep specialist in Scottsdale, Ariz., and author of "The Sleep Doctor's Diet Plan," points out that as the average length of sleep has declined in the United States, the average weight of Americans has increased.
Length of sleep (p = 0.011) and behavioural symptoms (p = 0.009) had significant associations with sleep satisfaction.
"Probably the restriction of movements by clothing could increase the length of sleep, and a cold environment makes swaddling possible without overheating," she says.
And although there are a lot of studies about the minimum hours of sleep needed, we all vary and the best gauge of how much sleep we need is how we feel after sleeping - if we don't feel refreshed throughout the day, our length of sleeping needs adjusting up or down until we find the perfect length for our own body's needs.
We are primarily concerned with two distributions commonly used to describe the lengths of sleep and wake bouts.
The distribution of bout lengths of sleep has been described as an exponential process in mice, rats, cats, and humans [3], [4], [6], while the distribution of wake bout lengths has been described as either exponential [6], or, more commonly, as a power law across these species [3], [4].
It has also been suggested that blacks have more extreme sleep durations than whites (22), which was consistent with our findings, as blacks were more likely to report short sleep and less likely to have sufficient sleep, and although the same proportion had long sleep, blacks were more likely to have extreme lengths of sleep (Supplementary Fig. 2).
Smoking decreased telomere length while the duration of sleep correlated positively with it.
