Sleep

Why is it that I can sleep sooo easily and not even notice it? I fell asleep watching t.v. today, and 5 hours later I woke up. Does this mean I'm sleep deprived, and I make up for it with incredibly long naps? Am I incapable of 'just taking a nap?' I like to sleep as much as the next person, but I hate just wanting to take a nap and not waking up. It's like my body wants more than 7 hours a day sometimes. Maybe I don't sleep well enough so I'm not rested. Here's some research:

Are You Sleeping Too Long?

Summarized by Robert W. Griffith, MD
May 7, 2004

Introduction

The question of how much sleep one needs has recently been raised again, based on a new study from Japan.¹ The Japanese Collaborative Cohort Study (JACC) enrolled 104,000 subjects aged 40 to 80, asked them about their sleep habits, and followed them for 10 years. Their conclusions: men tend to sleep longer than women, and the elderly sleep longer than younger people. Sleep duration of shorter or longer than 7 hours was linked to an increased risk of death from any cause.

Professor Daniel Kripke of the University of California, San Diego, has reviewed the known publications on optimal duration of sleep in a thoughtful editorial in the journal SLEEP. Here's a summary of what he has to say.

Sleeping too long is bad for you

The JACC study results are not actually original - similar findings have been reported from the Nurses' Health Study and the Cancer Prevention Study, and no studies have been described that refute them. But what's valuable about the JACC study is that it specifically enquired about sleep on weekdays, rather than overall, which clouds the picture because of the common 'weekend lie-in'.

The JACC results clearly show that 7 hours of sleep is better than the classically-assumed 8 hours. And for those who sleep only 5 or 6 hours on weekdays, there is no significant increase in mortality. So sleeping longer than 7½ hours has a worse effect than sleeping less than 6½ hours.

What other factors might have caused this result?

In several studies, symptoms of depression have been reported as being more common in people who sleep for longer or shorter than the ideal period of 6½ to 7½ hours. However, making appropriate adjustments for the presence of depression didn't alter the results of the studies.

Overweight is not generally associated with longer or shorter sleep duration, unless it's accompanied by sleep apnea. And the amount of snoring doesn't change the mortality risks of sleeping more than 7½ hours.

In the JACC study, those people who were less well (e.g. they'd had a stroke, heart attack, or cancer) were more likely to be long sleepers. But again, making adjustments in the analyses for these conditions didn't alter the results showing linkage between sleeping more than 7½ hours and increased mortality.

The Nurses' Health Study showed that having diabetes didn't affect the findings regarding the risk of mortality for those sleeping 5, 6, 7, or 8 hours, but was additionally harmful to those sleeping 9 or more hours.

What does this mean?

None of the studies of sleep duration provide a reason as to why sleeping more than 7½ to 8 hours a night is associated with increased mortality. A clear causal mechanism would go a long way to determining the significance of the phenomenon. More important, however, is the question whether people who sleep more than 7½ hours a night should make efforts to shorten their sleep time. So far, there are no trials of the effects of deliberate sleep restriction on long-term mortality rates.

From a practical point of view, it's probably enough to know that the ideal duration of sleep is 5 to 7½ hours. More or less is undesirable. There are good ways to address insomnia. And reducing your sleep from 8 to 7 hours would give you an extra hour a day to exercise your body and mind.

Source

• Do we sleep too much? DF. Kripke, Editorial. SLEEP, 2004, vol. 27, pp. 51--54

Footnotes
1. Self-reported sleep duration as a predictor of all-cause mortality: results from the JACC Study, Japan. A. Tamakoshi, Y. Ohno, SLEEP, 2004, vol. 27, pp. 51--54