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Reduced Sleep Means Reduced Physical Activity

Wednesday, January 06, 2010 Posted by Travis Saunders

Image by studentofrhythm.

In the past, I have mentioned that physical activity and sleep time are positively related - the more physical activity you perform, the more sleep you are likely to get.  Now most of these past studies have been observational, so we have a bit of a chicken and egg problem. By that I mean that we don't know whether:

A) Sleep deprivation causes reductions in physical activity,
B) High levels of physical activity make people sleepier, or
C) Some combination of A & B

Fortunately, an interesting experiment has just been published in the American Journal of Clinical Nutrition, which may help to untangle the cause and effect in this relationship. 

This new study was performed by Sebastian Schmid and colleagues, and I will warn you up front that the methods were a bit complicated.  I will do my best to explain them, but if you'd rather just take my word for it, skip the next paragraph.

In this study, 15 healthy young men experienced 2 conditions: 2 consecutive nights with 8 hours of sleep, or 2 consecutive nights of 4 hours of sleep.  Otherwise, both conditions were identical.  Half the men did the 4 hour condition first while half the men did the 8 hour condition first, and the two conditions were separated by at least 6 weeks for all subjects. After the first night in both conditions, the subjects were allowed to live a normal day, with the sole instructions being that they follow their usual eating habits, and avoid intense exercise.  After the second night, the subjects spent a day in a controlled laboratory setting, so that researchers could see how much food each participant ate from a series of buffets, as well as changes in appetite-related hormones.  Physical activity was directly measured using accelerometers, which is the gold-standard for measuring physical activity in this type of study.

So, what did the authors find?  Not surprisingly, physical activity was significantly lower following 4 hours of sleep as compared to 8 hours of sleep.  In addition to an overall reduction in physical activity following sleep deprivation, there was also a significant reduction in the proportion of the day spent in high intensity physical activity, and a greater proportion of the day spent in low intensity physical activity (unfortunately the amount of time engaging in sedentary behaviours is not reported, although one would assume that it increased following sleep deprivation).  Surprisingly, the authors did not find any effect of sleep deprivation on appetite-related hormones, which is in contrast with past research that has shown sleep deprivation to result in increases in both appetite-hormones and feelings of hunger.  There are of course some limitations (two that jump to mind: all subjects were healthy young men so we don't know if the findings will translate to overweight and obese individuals, and we have no idea how sleep-deprived these individuals were prior to the study) but the results are certainly interesting nonetheless.

So, what's the take-home message?

This is the first experiment to suggest that a reduction in sleep time can cause a reduction in physical activity.  This means that if you or your kids are hoping to live an active lifestyle, it's in your best interest to get a good night's sleep.  I don't think these results will shock anyone - when I'm tired, all I really want to do is sit down and relax.  It's important to remember that the amount of time watching TV, having a TV in the bedroom, and watching TV before bedtime, are all associated with sleep problems in children.  So if you want your kids to get a good night's sleep followed by plenty of physical activity, removing the TV from their bedroom is a great way to start (since screen time also predicts both caloric intake and obesity, this is really a no-brainer).  Spending less time around TV's and computers is probably a good first step for most of us adults as well.  As Peter mentioned earlier this week, the road to a healthier lifestyle usually involves many small steps, rather than drastic changes.  Getting a good night's sleep is a great way to start.

Travis Saunders

Schmid, S., Hallschmid, M., Jauch-Chara, K., Wilms, B., Benedict, C., Lehnert, H., Born, J., & Schultes, B. (2009). Short-term sleep loss decreases physical activity under free-living conditions but does not increase food intake under time-deprived laboratory conditions in healthy men American Journal of Clinical Nutrition, 90 (6), 1476-1482 DOI: 10.3945/ajcn.2009.27984

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3 Response to "Reduced Sleep Means Reduced Physical Activity"

  1. Kate Porter Said,

    I'm kind of confused about this part: "...following sleep deprivation, there was also a significant reduction in the proportion of the day spent in high intensity physical activity...", because in the previous paragraph you say that "...the subjects were allowed to live a normal day, with the sole instructions being that they...avoid intense exercise." If the subjects were specifically instructed NOT to do high-intensity exercise, how can they conclude that sleep deprivation reduces high-intensity exercise?

    Posted on January 6, 2010 at 1:20 PM

     
  2. Travis Saunders Said,

    Excellent point Kate. That is certainly a limitation of this study, especially when trying to apply these findings to daily life. Here is the exact quote from the paper itself:

    "[Subjects] were instructed to not deviate from their usual eating habits and to avoid intense physical activities (eg, working out) and naps
    during the day."

    It's a bit unclear whether the subjects were instructed to simply avoid intense physical activity, or specifically instructed not to "work out". I assumed (perhaps wrongly) that the instruction was aimed at preventing them from workout out, rather than high intensity physical activity that might be a natural part of the day (e.g. Running, rather than walking up stairs, or jogging for the bus, etc, all of which would probably be reduced in the sleep deprivation condition).

    Regardless of what they were instructed, roughly 25% of all physical activity fell into the "high intensity" range following 8 hours of sleep, while only about 20-21% of physical activity fell into the "high intensity" range following sleep deprivation (a statistically significant difference).

    Personally, I'd like to know whether people are more likely to skip a workout (or splurge on their diet) following a bout of sleep deprivation. Given the relatively small reduction in high intensity activity following sleep deprivation, it would also be nice to see other studies on this issue to see if that is a clinically relevant change.

    Anyone else have thoughts on the merits or limitations of the study?

    Posted on January 6, 2010 at 5:21 PM

     
  3. Dan Said,

    How's this for an added layer of complication:

    I have narcolepsy. I can sleep 12 hours a day and still feel like I haven't slept in days.

    I work in a warehouse. I've tried working desk jobs, but I've given it up because I can't sit still for very long without falling asleep.

    My doctor said that she has observed that people with narcolepsy tend to be obese, and yet eat less than the average person. We definitely tend to get less exercise, since we have no energy.

    Narcolepsy is thought to be caused by a lack of Hypocretin or Orexin, which is also known to regulate the metabolism. There hasn't been a study of caloric intake vs. exercise in people with narcolepsy, and there isn't likely to be one any time soon.

    I never exercise because I feel like it. I spent almost 2 years working out for 7 hours a week and didn't lose any weight. I didn't keep track of my calories, but I've been tempted to blame it on my narcolepsy.

    I also wonder if my constant sleepiness affects my appetite, or if my body is getting a constant "sleep deprivation" signal and is storing fat in response. How much of it is directly related to a lack of hypocretin vs. a secondarily?

    These things would be good to know so I could develop an effective plan to lose some weight.

    The good news is that I've lost about 6 pounds over the last month at my new job. I won't be surprised if my body adjusts and I stop losing it, or gain it back.

    Posted on January 25, 2010 at 7:47 PM

     

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We are PhD students in the School of Kinesiology and Health Studies at Queen's University in Kingston, Ontario. Our research focuses on the relationships between obesity, physical activity, and health risk. This blog is our attempt to consider the many "cures" for obesity that we read about on a daily basis. Enjoy.

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The opinions expressed here belong only to Peter and Travis and do not reflect the views of any organization. Any medical discussion on this page is intended to be of a general nature only. This page is not designed to give specific medical advice. If you have a medical problem you should consult your own physician for advice specific to your own situation.

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