We all know that getting a good amount of sleep regularly is important for health. But, are you really getting as much sleep as you think? Most of the research as been done with self-reported sleep data, which is not necessarily a bad thing. They are relatively easy to obtain, inexpensive, and un-invasive; but, people tend to report themselves in a favorable light, and this distorts the true relationship between sleep and health to some degree.
The studies that looked at self-reported and objectively measured sleep duration has found that, in general, we tend to over-report sleep duration.1 The over-reporting is actually higher amongst ‘short sleepers’ than ‘adequate sleepers’. For instance, those who slept 5 hours (measured by actigraph) over-report their sleep duration by 1.2 hours, which is they thought they were sleeping for 6.2 hours. Those who slept 7 hours only over-reported their sleep duration by 0.4 hours, i.e., they reported sleeping for 7.4 hours. Thus, most people are still a good judge of their sleep duration but their judgment is more likely to be closer to the truth if they slept enough. For these people, often the difference is only 30 minutes or so, even though research suggests only weak-to-moderate relationship between self-reported and objectively measured sleep exists.2
Sleep requirements also change across the lifespan,3,4 and your ability to perceive sleep also changes with age. Indeed, ageing is commonly blamed for decreased sleep duration and quality3 but these decreases are not as big as one would guess−the strongest association was about 10-minute decrease per decade in women. In fact, a study in women found that postmenopausal women get more sleep and better quality sleep than premenopausal women.5 But, the difference in sleep duration was only about 10 minutes. In general, women tend to sleep 20-30 minutes more and experience greater deep sleep than men.3 Men, on the other hand, experience greater arousals but take a shorter time to fall asleep than women.
Figure 1: Adjusted sleep stages according to age for men and women3