Sleep! It's probably the one single thing we spend the most time doing. If you do it eight hours a night it means that you spend literally one third of your life asleep. Most of us are getting less than that and we probably need more. Sleep is important. It's also the topic of this week's Healthcare Triage.

So how do you figure out how much sleep people need? These days, it's hard to know. After all, modern society has changed how and when we sleep. We have electrical lights that allow us to be productive at night. We have coffee to wake us up in the morning. We'd have to return people to a simpler life to find out how much sleep is 'natural'.

You gotta love scientists! They did just that. They got five healthy adults to live in a Stone Age style settlement for eight weeks in Southern Germany. No electricity, no running water, no internet or modern conveniences. They slept on brushwood and firs. They had no alarm clocks. They had only a campfire for light at night. Germans, man. And what happened?

Before the study, the five adults fell asleep on average at 11:42 p.m. but under Stone Age conditions, they went to bed at 9:37 p.m. After the experiment they went back to their old habits, falling asleep at 11:07 p.m. Waking time didn't change as much. Before the experiment they woke up at about 7:02 a.m., in Stone age conditions they woke up at 6:28 a.m. and afterwards they went back to 7:14 a.m.

Sleep time increased too. They went from an average of 5 hours and 42 minutes before the experiment to 7 hours and 12 minutes in Stone Age conditions. Then, back to 5 hours and 13 minutes after.

So they weren't sleeping naturally outside of the experiment. But the 'natural' amount wasn't eight hours. It was about seven and a quarter hours.

The National Sleep Foundation published a survey of people's sleep habits in six countries. Canadians and Mexicans sleep the most at 7.1 hours a night. Then Germans at 7 hours and citizens of the UK at 6.8 hours. At the bottom were the US at six and half hours and Japanese at 6.4 hours.

People are also sleeping less than they used to. In the early forties almost 85% of Americans got seven hours or more of sleep. By the 1990s and continuing to today, less than 70% of people get that much sleep.

Richer people also get more sleep than poorer people. Only about a third of people in the United States making 75,000 a year or more get less than six hours of sleep a night. On the other hand almost half of people making less than $30,000 a year get less than six hours a night.

We also sleep pretty inefficiently. We spend too much time in bed not sleeping. We're watching TV or surfing the internet. We're drinking at night. We even exercise before bed. And all of these things make it less likely that we're going to sleep efficiently.

Kids generally need more sleep. And it's easier to try to figure out how much babies need to sleep 'cause we let them be. The National Heart, Lung, and Blood Institute recommends that newborns get 16 to 18 hours of sleep a night. Lots of them get that because, again, we let them. Only a fool wakes a sleeping baby. I've had three of them and I'm telling you that's the case.

Preschool age kids are recommended to get 11 to 12 hours of sleep a night, and fewer get that. School age children should get at least 10 hours of sleep a night, and they don't. And teens usually need 9 to 10 hours a night and lots of them don't get that. The median three year old gets about 11 hours of sleep in the United States. The median eight year old gets about 10 hours of sleep. The median teenager gets about 9 hours of sleep. That means about half of all these kids are getting less sleep than they likely need, especially the teens.

And not getting enough sleep can lead to some bad and often strange consequences, but those are the topic of next week's Healthcare Triage. Let's put that off for now.

This week I'd like to end by focusing on some recent news that getting too much sleep might be bad for you. The Wall Street Journal had an article this summer entitled Why Seven Hours of Sleep Might Be Better Than Eight. It highlighted a study published in JAMA Psychiatry in 2002 entitled Mortality Associated with Sleep Duration and Insomnia. The study followed more than a million people with cancer. They found that people who slept between six and a half and seven and a half hours a night on average had a lower mortality rate than those who slept more. The article also noted some research that showed that people who slept more than seven hours a night had lower cognition scores as well.

But correlation is not the same as causation. You can't forget that it's entirely possible that sicker people might have needed more sleep and gotten it. In other words, it's possible that being sick leads people to sleep more, instead of more sleep leading to illness. But all this misses the point. People likely need very different amounts of sleep. A recent New Yorker article summarized much of the research on sleep and genetics and posited that about 80% of the variation in people's need for sleep is genetic. So maybe you're not getting enough sleep. If you're getting less than six to seven hours a night, that's probably not enough. But if you feel great and you're doing well, don't sweat it. Don't force yourself to get more just because of some published average.