What is the right amount to sleep?

photo-177I’ve been trying to figure out lately how much sleep I need. I used to assume I needed the standard 8 hours per night, but after tracking my time for multiple weeks over the years, I’ve realized that’s not the case. It tends to average out around 7.5 hours/day over a week (so 52.5 hours or so). I probably wake up every other night to go to the bathroom in the middle of the night, and sometimes it takes me a bit longer than other nights to get back to sleep, which lowers my actual total a bit from 7.5 hours.

But I don’t think I’m sleep deprived. I’m not pounding coffee all day. I have one cup in the a.m. On weekends I usually wake up pretty early (sometimes before the kids, sadly enough). Last night, the last time I saw on my clock was 10:45 and I woke up a few minutes before 6, which was long before I’d set my alarm. I’m sure this has something to do with summer and the early light, but I let myself lie there in bed and slowly open my eyes before hopping up around 6:15 to go for a run. Then again, other days I sleep a bit longer. I went to sleep around 11:20 on Monday night and woke up at 7:15 on Tuesday morning. We all got a slow start that day. Fortunately, the kids still made it to camp on time.

So I’ve been interested to see the reaction to a story in the Wall Street Journal yesterday suggesting that 7 hours, not 8, might be the right amount to get. As with all studies and recommendations, this is a tricky thing to say for sure. Generally, people say that “7-9 hours” is ideal for adults, but some analyses of broad studies and mortality data suggest that the lower end of that range is associated with lower risks. Again, you can’t control for everything. People who are ill might sleep more, but it’s not the sleeping more that’s the problem — it’s the underlying health condition. But it does suggest that getting less than 8 hours a night, and perhaps even a wee bit under 7, isn’t something to worry about.

Unless you’re falling asleep at the wheel. Then it is — and you need more sleep.

As I’ve been looking at data from the Mosaic Project, I’ve been realizing a few things. First, the vast majority of women in the project (about 90 percent) got at least 7-9 hours/day averaged over the week. Bad days were pretty rare. Only 37 of 1001 days featured less than 6 hours of sleep. No one averaged less than 6 hours/day when tallied over the whole week (42 hours over 7 days) but in my sleep section, I did look at the women who averaged between 6-7 hours/day, with the assumption that this was lower than ideal. Now that I know at least one study looking at 1.1 million people found that sleeping 6.5-7.4 hours was associated with lower mortality, I may have to reconsider the phrasing. Most people who were under 49 hours/week were over 45.5 hours (6.5 hours/day).

Of course, averages mean nothing about individuals, and if you need 8 hours/day and are getting 6.5, that can be a problem. But I shouldn’t assume, on its face, that getting a bit less than 7 hours is bad.

One other finding: When people think about sleep, they think about “typical” nights. But there are no typical nights. Just comparing two adjacent weekdays — Tuesdays and Wednesdays — I found that 22 percent of women showed gaps in sleep totals of 90 minutes or more. Sleep variances are frequent, and probably contribute to muddled findings on how much sleep people need.  

How much sleep do you think you need? Do you get that most nights? Are there big variances?

In other news: Modern Mrs. Darcy has a guest post from a woman who managed to achieve big things in her personal life by shifting a mere 2 hours of her work schedule around. We often think that change requires a lot of shifting, but if you’re focused and mindful, you can do a lot with a little.

Photo: A hotel bed. I sleep extra well in these.

16 thoughts on “What is the right amount to sleep?

  1. One thing to keep in mind is that your mosaic project is already focused on a VERY specific subset of the population… and without qualitative discussion from the sleeper (i.e. how restful/restorative was the sleep?) I don’t think the numbers tell you a whole lot beyond how TIME was spent.

    1. It doesn’t even tell you that. All of this is self report. We have no idea how much these people are actually sleeping.

  2. I think part of the differences in results may reflect the age of the population being studied. My layman’s understanding is that older people need less sleep than middle aged people. The age of the study participants was only given for the Sleep Medicine study from 2011 where the participants are described as elderly. That may be why they came up with a lower optimal amount of sleep – 5-6.5 hours – than some of the other studies. However, I’d hesitate before drawing conclusions about sleep needs for populations other than elderly women (such as your blog readers and Mosaic participants).

    The mean age for the UCSD study is late 50’s – so possibly a very different sleep need than than the previous study – which is probably why they find the lowest mortality in those who get a greater amount of sleep – 6.5 hours – 7.5 hours. I’d be inclined to think your Mosaic/blog reading population is more like this group in sleep need and – turns out from your analyses of time logs – they are.

    Another point to make is the differences in outcomes studied. Getting a bit less sleep may be associated with cognitive declines but not mortality – probably and fortunately – because while middle-aged people in the US can have temporary cognitive deficits, they aren’t all that likely to die.

    So from the research presented I’d say that somewhere around 7ish hours is probably about right for a healthy US population of middle-aged adults. As you mentioned, sick people are probably the ones sleeping very short and very long periods, which are why they are associated with mortality (rather than being lazy and sleeping a lot being associated with mortality).

    Personally, now that I have my Fitbit and can actually track sleep fairly accurately, I can say that I feel better with 8 – 9 hours of sleep when my body is under stress (say training for races or pregnant and moving) but – so far – I’m not more likely to die than if I got 7 hours of sleep.

    1. @Chelsea – thanks for this. Yes, cognitive decline and morbidity are not the same thing, so good to know what outcomes we’re looking at. The 5 hours figure did seem pretty low to me — and given that so few people slept anywhere near that range in my study I wouldn’t think it would be particularly natural for a lot of people (at least in that demographic). I think I read recently in Runner’s World about the sleep schedules of elite runners. They slept a lot! And they’re probably pretty healthy…

  3. Ahh, my favorite topic 🙂 I am looking forward to an entire WEEK of hotel bed, most of it by myself.

    Some personal observations:

    1. When I am eating better (which for me approximates a Paleo-ish diet) I need less sleep. I’ve found that eating more than a serving of grains at a meal makes me MUCH more tired during the day. It’s kind of a dramatic change.

    2. Same is true for regular exercise – when I’m getting even just a 30-40 min walk on most days, I sleep a lot better at night.

    3. I’ve discovered a weird pattern where I feel better if I sleep either 6 or 9 hours. Anything in between makes me pretty groggy for a while after waking – probably a sleep cycle thing. In college, I also sometimes had to make do with 3 hours and that was actually *better* than 4 or 5.

    I remember reading something about figuring out your ideal sleep schedule (times and duration) while on a 2 week vacation. Spend the first couple of days “catching up” then really observe when you feel tired at night and when you naturally wake in the morning. Of course, that doesn’t really work if you have earlybird kids who need stuff in the morning, but I hope to try it someday 🙂

  4. I have been using the sleep cycle app for about a month now. I average about 6.58 hours of sleep a night including the nightly wake up from our 2 1/2 year old daughter crawling into bed with us, which I hope is a phase.
    Personally, I don’t feel sleep deprived, though I am tired when waking up, but the app does seem to be helping with that front. I also found that power napping also helps. 2 naps a week really gives me an edge.
    Another thing that has helped has setting a wind down alarm for night with my wind down tasks for the day. The first of which is turning off all screens. This 20 – 30 minutes has been critical in low stress mornings and maximizing productivity.

  5. I’ve found that when I put pressure on my sleep cycle – for example, I go to bed late but set my alarm back significantly earlier than normal – I will sleep through the alarm and wake up almost exactly 8 hours after I went to bed. Note I said ‘went to bed’, not fell asleep, though I don’t think there’s a big gap.

    I think this could be a good way of determining your natural sleep length. Has anyone read any studies to that effect?

    I would still love to be able to manage my time better by going to bed earlier and waking up earlier. I have not been able to make that happen…

  6. I’m halfway through a book by Alan Lakein’s “How to get control of your time and your life”,he discussed about sleep time and he said doctors have found that often,many people spend many hours in sleep for which there is no physical need.That we might experiment reducing our sleeping time by half hour and get adjusted to this new pattern-as long as we are as effective as we were before we will gain the equivalent of a week of Sundays in the course of a year.

    1. That’s a pretty old book. I’m not against the experimentation, I’m just saying there’s a lot of water under the bridge between today and the studies Lakein is talking about.

  7. For me personally, eight hours is good. If I get the odd nine hour night here and there, it’s fine, but if I regularly get nine hours, I start to have trouble falling asleep at night.

    And a few nights in a row with less than eight hours start to make me feel a little weary.

    I base my sleep schedule on what makes me feel good, not on any particular study. I don’t really care if a study says 7 hours is ideal because I know I start to feel like crap on 7 hours!

  8. We spend a lot of time discussing amount of sleep, but not quality of sleep. I remembering reading years ago that trees and plants were affected by light pollution, I would think that would apply to humans as well, especially with how much time we spend looking at screens. I think we tend to believe we are not getting enough sleep, because we aren’t getting enough of the restorative sleep we need. I also, think diet and exercise play a huge roll. Not enough people feel they have enough control in their lives to focus on diet, exercise and sleep. All things that lead us to becoming more obese as a society.

  9. I took your advice and have moved my wake time up about two hours a day. I enjoy the time a great deal, so I’m not tempted to skip it to have a lie-in, but I’m also a TBI survivor, so I’m well aware that proper rest isn’t something I can play fast and loose with.

    I find I wake 15-30 minutes before my alarm, which is about 7.5 hours. But a couple of times a week, I feel like it’s not a good idea to get up and I sleep for another 90 minutes, or a full REM cycle. From what I can tell, this tracks with how long or hard I work during the days previous (it definitely tracks with long, but hard is subjective, so I haven’t tracked that adequately.)

    1. @Shanna – interesting. I’ve definitely heard about the 90 minutes or 3 hour cycle issue — that waking right at the light stage is key to feeling rested. I think that’s one of the upsides of the step counters that monitor sleep too. Mine doesn’t have that function.

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